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VIDEO OTOSCOPY OBSERVATION & REFERRAL:
The FDA Red Flags
by
Max Stanley Chartrand
Introduction
Within the eight brief “red flag” otological-screening
provisions of the U.S. Food & Drug Administration
Hearing Aid Rule we find inclusive, comprehensive and
uniform standards of observation for professionals
involved in evaluating hearing status, dispensing
hearing instruments and assistive devices, and making
medical referral1.
Codified into federal regulation in 1977, the wisdom and
foresight contained in these provisions have withstood
the test of both time and experience. To this day, the
regulation in its current form continues to assure
consumers that medically treatable cases of auditory
deficit, except those exempted by informed consent2, can
and will receive medical treatment before non-medical
solutions are pursued.
Though statistics show that approximately 90% of the
hearing impaired population over the age of 18 suffer
from non-medically treatable forms of hearing lesions, a
very important 10% of the population do need and often
respond successfully to medical treatment, when referred
by dispensing professionals3. In a 1993 FDA field
survey, it was found that 69% of patients utilized the
waiver, the remainder opting to see their physicians
before purchasing hearing aids, or about three times as
many patients that statistically would be expected to
require medical intervention4.
More importantly, advancements in research, technology,
and professional education continue to open greater
understanding of the many conditions that can
potentially come under the current red flags. This
ongoing development of knowledge requires that all
dispensing professionals take more careful note of
prospective hearing aid patients’ medical and health
status, including medications, and to work more closely
with their family and ear physicians.
The advent of video otoscopy
Going from ordinary incandescent otoscopy to fiber optic
to daylight-quality halogen-lamp technology has provided
hearing health professionals with a great deal more
information under routine inspection of the ears. But
the single largest leap in technology came in the early
1990s with the advent of the video otoscope. This
technology is still evolving as it enters the digital
age. Freeze frame photography, wide-angle lens, blown-up
onto high definition SVGA screens reveals even more
microscopic information.
Video otoscopy is fast becoming a standard part of daily
dispensing practice, as evidenced in recent surveys (see
figure 2)5. Video otoscopy is also being built into real
ear, programming and audiometric equipment, database
patient management systems, and other diagnostic
applications. If current trends continue it will only be
a short time before video otoscopy is completely
mainstreamed into every aspect of dispensing practice.
Improved observational capabilities suggest the need for
increasingly more sophisticated continuing education and
increased standards of practice, as well more
interaction between allied professionals. It is the
purpose of this paper to stimulate that movement, by
listing a large array of oto-related conditions that may
be better observed utilizing video otoscopy and through
a more thorough case history interview than though
conventional otoscopy.
Red Flag Review
These eight red flags provide for a host of conditions
that may be observed during the patient case history and
otoscopic examination. In most cases, the pathologies
needing medical attention present within the external or
middle ear. These include infection, allergy, trauma,
deformity, and impaction. Other cases may involve
possible cochlear, retrocochlear, or central
pathologies. Therefore, it is important that dispensing
practitioners be highly skilled in otoscopy, case
history taking, and in recognizing potentially treatable
conditions requiring medical referral.
“A (hearing health professional) should advise a client
to consult promptly with a licensed physician,
preferably a physician that specializes in diseases of
the ear, if the (hearing health professional) determines
through inquiry, actual observation, or review of any
other available information concerning the prospective
user, that the client has any of the following
conditions (updated language in parentheses):
1. Visible congenital or traumatic deformity of the ear.
2. History of active drainage from the ear in the
previous 90 days.
3. History of sudden or rapidly progressive hearing loss
within the previous 90 days.
4. Acute or chronic dizziness
5. Unilateral hearing loss of sudden or recent onset
within the previous 90 days.
6. Audiometric air-bone gap equal to or greater than 15
decibels at 500 Hz, 1,000 Hz, and 2,000 Hz.
7. Visible evidence of significant cerumen accumulation
or a foreign body in the ear canal.
8. Pain or discomfort in the ear.”
Flag #1: Visible congenital or traumatic deformity of
the ear.
Throughout the literature are identified myriad
variations in size, shape, texture and coloration of the
anatomy of the human ear, both normal and abnormal.
Dispensing professionals should be able to recognize
those differences, and to refer for congenital, acquired
and traumatic deformities.
The term congenital connotes conditions that have
existed since birth, i.e. whether developmental,
deprivation or disease processes. Congenital ear
deformities requiring reconstructive surgery are
estimated at approximately 1 in 15,000 births in the
U.S. population, such as the
Treacher-Collins-Franschetti syndrome, a polygenic
multifactorial developmental abnormality. Microtia and
atresia may be accompanied by un- or under-developed
middle ear ossicles, and orthodontic/mandible
structures6.
Examples of acquired deformities are osteoma,
hyperostosis, and exostosis7. Each represent a bony
malformation of the external meatus canal often causing
a narrowing or blockage of the canal opening toward the
tympanic membrane. Traumatic deformity may involve a
slap on the ear, blow to the head, violent explosion,
extreme noise (>120dBSPL), hazardous chemical exposure,
or embedment of a foreign object8. Deformities arising
from trauma take forms too numerous to describe here.
Evidence of bleeding, burns, swelling, discoloration,
bone fracture, perforation, hemotympanum, and/or
non-specific inflammation present reason for referral.
Other trauma-induced conditions include cauliflower ear,
perichondritis, and acquired atresia of the meatus.
Other deformities caused by disease may include:
-Precancerous, benign, and malignant tumors, growths
-Hematoma of the auricle
-Mastoiditis with subperiosteal abscess
-Herpes zoster oticus
-External or middle ear cholesteatoma
-Nodular melanoma
-Ulcerated squamous cell carcinoma
-Senile keratoma
Flag #2: History of active drainage from the ear in the
previous 90 days.
Suppurative exudates refer to the flow of pus from any
part of the ear9. Etiology is determined via laboratory
tests. However, the dispensing professional should have
at least a rudimentary understanding of these
conditions, and their associated pathologies:
Nonspecific Inflammation of the Ear. Allergy, dermatitis
and diabetes mellitus can lead to chronic inflammation,
epithelial atrophy and dry scales. In such cases the
keratin layer of tissue is missing or separating from
the epithelium. Chronic cases bring cycles of swelling
and purulence, which can significantly interfere with
the patient’s ability to wear an earmold. Repeated
episodes can cause maceration (soaking) of the meatal
skin by purulent fluid until there is a reduction in
elasticity of the skin and atrophy of the ceruminous and
sebaceous glands. Keratin protein is also missing in
most cases10. Disturbance of the pH balance of the
tissue results, promoting growth of anaerobic amoeba
(pseudomonas), fungus, yeast, and/or bacteria.
Bacterial and Viral Otitis Externa. Swimmer’s ear is the
common reference to a variety of bacterial and viral
external ear infections11. Because of long periods of
maceration (soaking) of the ear canal tissue and deep
penetration of viral organisms, there is often a
deep-seated phlegmonous suppurative inflammation.
Pseudomonas. Refers to a specific genre of anaerobic
gram-negative organisms that often produce a most
stubborn form of external otitis, especially for
diabetics (including pre-, latent or manifest diabetes),
or others with significant pH imbalance or autoimmune
deficiency12. Left untreated this serious form of
infection may cause insidious osteomyelitis of the
temporal bone. Further, because pseudomonas is highly
resistant to antibiotic therapy, under conservative
treatment it may insidiously progress to the skull base
because of deep tissue involvement, making it a
potentially fatal disease13. It is the experience of the
author that many of these cases can be latent and
longstanding, and easily missed during a cursory medical
examination. However, upon the fitting of a hearing
instrument, providing an anaerobic environment, can
expose the presence of latent pseudomonas. In such
cases, it is critical that the dispenser and
otolaryngologist discuss their observations.
Staphylococcus Aureus. This bacterium is considered the
most common form of acute or chronic external otitis
affecting approximately 10% of the U.S. population each
year, primarily children14. Often there is a history of
trauma by scratching, gouging, or using cotton swabs
just prior to symptoms. In acute cases, the external
meatus may close entirely due to edema, exudates (pus)
and desquamation (shed tissue) as the bacterial medium.
Pain is often evident while manipulating the pinna or
surrounding tissues. Staphylococcus usually responds
well to antibiotic therapy.
Furuncles. Sometimes described as a boil or skin
abscess, can cause pain and swelling as well as purulent
exudates. In such cases, latent or manifest diabetes may
be at the root.
Herpes Zoster Oticus. Herpetic vesicles around the
pinna, in the ear canal, and, sometimes, on the tympanic
membrane characterize this disease. Becoming
increasingly more common, medical referral and treatment
is advised.
Otomycosis. A fungus, usually fungal mycelium, causes
this common condition. Complaints are of itching, rarely
of pain. Hence, a high incidence of such cases may be
seen in the dispensing practice. Such cases should be
cautioned about the use of Q-tips, which can cause the
growth of other (secondary) bacteria. If whitish-yellow
exudates are visible, hearing aid use is discouraged
until antifungal treatment is completed.
Eczema of the Ear. Similar to otomycosis, eczema may
take either the bacterial or fungal forms15. Continual
exposure to moisture and absence of keratin tissue
causes growth of pathogenic bacteria or fungi,
especially with an earmold inserted. Fluctuation between
inflammation, swelling, and drainage, and drying,
scaling, and general irritation, this disease must
receive medical attention to be brought under control.
Note: some forms of eczema are caused by contact
dermatitis or allergy to hair sprays, cosmetics,
eyeglass frames, earmold plastics, cortisone use or
antibiotics.
Flag #3: History of sudden or rapidly progressive
hearing loss within the previous 90 days.
Any sudden or rapidly progressive hearing loss would
preclude dispensing activity until medical assessment.
Many such cases need emergency attention, so it behooves
the dispenser to refer to a physician immediately.
Etiology could be trauma, infection, disease, cochlear
stroke, allergy or ototoxicity. Below are listed some of
the more frequently reported causes of sudden deafness:
Trauma
-temporal bone fracture
-labyrinthine (cochleovestibular) concussion
-direct injuries to middle or inner ear
-barotrauma (drastic air pressure changes)
-Caisson disease -acute acoustic trauma or catstrophe
-mechanical incursion
-foreign body incursion
Viral Disease
-mumps, measles, chicken pox
-influenza (neuritis statoacoustica)
-adenovirus, whooping cough
-scarlet fever, diphtheria, Coxsackie
-viral cochleitis, herpes zoster otitis
-epidemic parotitis, meningoencephalitis
Bacterial Disease
-Meningitis, bacterial labyrinthitis
-Richettsiae, Toxoplasma gondii
Ototoxic Aminoglycoside Antibiotics
Streptomycin, dihydrostreptomycin, neomycin
kanamycin, gentamycin, vanomycin, viomycin
paranomycin, tobramycin, amikacin sulfate
Other Ototoxic Drugs
-salicylates (aspirin), iodine
-sulfa drugs, quinine
-novocain, barbiturates, morphine, chloroform
-furosemide, mannitol, hydrochlorothiazide (diuretics)
Other Known Ototoxic Substances
-caffeine, alcohol, nicotine
-lead, mercury, arsenic compounds
-organic phosphate compounds, sulfur compounds
-tetrachloroflourocarbon compounds, carbon monoxide
-benzol, nitrobenzol, aniline dyes
Tumors of the Middle and Inner Ear
-glomus tumor, osteoma,
-middle ear carcinoma, cholesteatoma (benign)
-acoustic neuroma, vestibular schwannoma16
Meniere’s Disease, while a suspected cause of sudden
deafness, will be discussed at greater length in the
next section under “acute or chronic dizziness”. For our
purposes here it is important to point out that the
three symptoms comprising this malady (tinnitus,
deafness, and vertigo) may converge simultaneously or
occur separately. The normal course of the disease (or
syndrome) is often sudden and episodic. Its most
pronounced symptoms usually vanish by the time of
examination, leaving in their wake a progressively
damaged hearing and balance peripheral organ. Often
considered idiopathic, the most common causes are
recognized as allergy, especially food allergy,
lipoproteinemia (high blood lipids), ototoxicity
(medication), and vascular disease.
Psychogenic forms. The discussion pertaining to sudden
deafness would not be complete without some mention of a
non-organic form of “sudden deafness” or
psuedohypoacusis. “Hysterical deafness” is the
vernacular for the form arising from tragic personal
loss or acute emotional trauma17.
Flag #4: Acute or Chronic Dizziness
There are numerous medical conditions that can cause
complaints of “dizziness”. Many of the foregoing
conditions mentioned above, whether disease, trauma, or
ototoxicity may elicit such complaints. However, we must
distinguish here between dizziness and vertigo.
Dizziness may or may not involve ear pathology, but can
be associated with nausea (vagus reflex in the stomach),
giddiness (hyperventilation), faintness (asphyxia), or
light-headedness (circulatory constriction). Vertigo, on
the other hand, is a vestibular disorder affecting
spatial nystagmus subjectively signaling an apparent (or
visual) movement of the environment. Other forms may
include ataxia and rototary vertigo18, both of which
should be referred to a physician for immediate
investigation. Perhaps medication is a cause, or serious
otopathological illness, such as viral cochleitis,
cochlear stroke, vestibular dysfunction, acoustic
neuroma or Meniere’s.
Meniere’s Disease/Syndrome (or endolymphatic hydrops),
as mentioned earlier, exhibits the triumvirate of
tinnitus, deafness, and vertigo. Many sufferers complain
of “roaring ears” and episodes of “dizziness” (vertigo),
without an awareness of the hearing loss component.
Post-attack symptoms may include nausea, vomiting, and
fullness in the ear. In the early stages, hearing
thresholds tend to be affected most in the low
frequencies, while later stages may bring permanent
deafness affecting the entire spectrum. Fluctuating
thresholds require bracketing of audiometric readings
until stabilized. Studies show incidence of Meniere’s to
be approximately 80% of cases unilateral and 20% cases
bilateral19. Episodes may last from a few minutes to
several days. The pathogenesis of Meniere’s is found
first in the quantitative imbalance of the
cochlear-vestibular fluids, perilymph and endolymph.
Separating the two fluids is the Reissner’s Membrane.
When the resorption of the potassium-rich endolymph
fluid is impeded, a build-up of pressure (hydrops)
occurs, sometimes causing the Reissner’s membrane to
rupture, and the mixing of the two asimilar fluids. This
can lead to a more generalized and permanent form of the
disease, leaving in its wake deafness, severe tinnitus,
diplacusis (cochlear distortion), recruitment (abnormal
loudness growth), and general vestibular dysfunction
(vertigo).
Flag #5: Unilateral hearing loss of sudden or recent
onset within the previous 90 days.
Much of what has been covered in flags #3 and #4 applies
to this section. Many pathologies of the ear appear
unilaterally. Trauma and disease are generally
unilateral depending upon the degree of exposure
bilaterally. Cases that appear suddenly (defined in the
regulation as within 90 days from onset) should be
medically assessed before proceeding with auditory
rehabilitation.
Flag #6: Audiometric air-bone gap equal to or greater
that 15 dB at .5KHz, 1KHz, and 2KHz.
While an air-bone gap of only 15 dB at 500Hz may not
seem important in the overall scheme of things, when it
also extends to 1,000Hz and 2,000Hz, a significant
medically treatable condition may exist.
For instance, a simple Eustachian tube blockage or
irritation such as found in a mild inhalant allergy or
change of altitude (air pressure), can easily produce an
air-bone gap of 15dB or greater at the relatively low
frequency of 500Hz. Even barometric pressure changes
have been found to cause similar affects in individuals.
But, in each of these cases, involvement of the mid and
high frequencies may indicate a deeper, more permanent
problem. Some manifestations that may cause such an
air-bone gap are:
·Closure of the tragus or atresia of the external ear.
·Obstructions in the external meatus such as:
accumulated cerumen, exudates and debris accumulation,
foreign object, otitis externa, fungus, pre-and
cancerous growths, osseous formations, collapsed canal,
or some mandible abnormalities.
·At the tympanic membrane: perforation, post-infection
or surgical scar tissue, thickening from
tympanosclerosis, extreme flaccidness, disarticulation,
or fluid, cholesteatoma, glomus tumor, or air pressure
arising from Eustachian tube dysfunction.
·Within the middle ear: disruption of impedance
transformation or immobilized ossicles, otosclerosis,
disarticulation, tensor tympani or stapedial muscle
abnormalities, disruption of differential transfer at
the oval or round windows, or fluid accumulation, otitis
media, mastoiditis, cholesteatoma, glomus tumor, or
again unequalized air pressure.
Flag #7: Visible evidence of significant cerumen
accumulation/foreign body in the ear canal.
Until the advent of high-definition video otoscopy, this
provision of the regulation has been the main focus of
otoscopic discovery in dispensing practice. But as one
may see from the foregoing, cerumen accumulation is only
one of a multitude of possible concerns20.
“Impacted” cerumen presents several challenges:
·Conductive hearing loss, often accompanied by objective
tinnitus, chronic cough (vagus), tearing eyes,
interaural attenuation, and/or complaints of occlusion.
If cochlear hearing is otherwise normal, the audiometric
pattern is quite pronounced in the lows (usually about
40-60dB), rising to near normal in the highs. In cases
of sloping of those with high frequency sensorineural
impairment, air conduction thresholds tend to be “flat”
in configuration.
·Obstructed otoscopy of the canal and tympanic membrane.
·Inability to perform impedance audiometry, acoustic
reflex, electronystagmography (ENG), otoacoustic
emissions, probe mic, and other tests in the clinical
battery.
·An accurate ear impression cannot be taken.
·The use of a hearing aid is impossible or impractical.
·Other pathologies may be obscured, causing delay in
treatment.
“Significant” (but not impacted) cerumen accumulation
may present these challenges:
·While thresholds may not shift per se, other
complications may occur, such as erroneous probe mic and
tympanometry results, and a loss of natural ear canal
resonance.
·Obstructed view of the canal and TM landmarks,
incomplete otoscopy.
·Occlusion or fullness may still be a factor in some
individuals exhibiting a sensitive vagus (Xth Cranial)
reflex
·Interaural attenuation, if traces of cerumen adhere to
the tympanic plexus region of the pars tensa.
·Difficulty in taking a proper ear impression, causing
mechanical impaction.
·Other pathologies may go undetected.
Flag #8: Pain or discomfort in the ear.
In determining course of action with this flag, careful
and informed judgment must be exercised. For instance, a
number of spurious neurological artifacts unrelated to
otological status can be identified by patients as
“pain” or “discomfort”. Examples are: dental
oversensitivity, TMJ, sinus allergy, and facial nerve
artifact, any of which could be mistaken for pain in the
ear. These often have cross-action with ear-related
nerves at either the mandible or tympanic plexus of the
tympanic membrane.
Having said this, however, it is important to note that
even these reports can and probably should be reported
if they are not already under the care of a physician.
The evaluator should always inquire deeper as to past
history of the complaint, as well as note if it has been
medically evaluated, by whom, and the course of
treatment.
To determine correlation between reports of pain or
discomfort and actual otological events, visual
assessment should also be made for presence of swelling,
redness, exudates, etc. Pain arising from the trigeminal
(jaw, teeth, gums) could as easily result from
mandibular or orthodontic abnormalities, neighboring
sinuses and lymph glands (facial), or a host of
contusions, swellings, and infections only peripherally
proximate to ear anatomy. Sinus allergy can cause an
“earache”, etc.
Pain, nevertheless, is a motivating factor for patients
to seek help. And though its management is generally
outside the scope of practice of dispensing
professionals, medical referral is often needed, because
serious ear and non-ear related disease or pathologies
might exist. On the other hand, serious ear disease,
trauma, or acquired abnormality can also be the source
of the complaint, and should certainly be referred for
immediate medical assessment
An Opportunity to Build Interdisciplinary Teamwork
In the spirit of the FDA Hearing Aid Rule of 1977, one
of the most important intentions of its framers was the
building of cooperative community teams among hearing
healthcare professionals21. Certainly, consumers of
hearing healthcare come out better when local health
professionals work together in best meeting their needs.
Two current initiatives---America’s Hearing Healthcare
Team Initiative and the BHI Physician Referral
Development Program---are just two of several major
efforts to instill greater cooperation between the
various disciplines. The FDA Hearing Aid Rule of 1977
was designed to assure the “glue” that will bring
hearing health professionals together and foster that
kind of teamwork. The focus is, as always, on the well
being of the patient, with each member of the team
working toward providing the best possible outcome.
Dr. Chartrand serves as director of research for
DigiCare Hearing Research & Rehabilitation, and as
instructor for the International Institute for Hearing
Instruments Studies and the American Academy of
Audioprosthology. Correspondence: P.O. Box 706, Rye, CO
81069, or by faxing (719)676-6882, digicarenet@aol.com.
References
1. U.S. Food & Drug Administration Rules and Regulations
Regarding Hearing Aid Devices: Professional and Patient
Labeling and Conditions for Sale, Part IV, Federal
Registers, 9286-9296, February 15, 1977
2. U.S. Department of Health & Human Services, Title 21
Code of Federal Regulations: Part 801-Medical Device
Labeling, 4/1/91
3. Bove, C., Administrative Meeting of the Enforcement
Division of the U.S. Food & Drug Administration, Silver
Spring, MD, (1993).
4. Author’s September, 1993 meeting with Division of
Compliance Operations (HFK-116) to determine what
constitutes appropriate compliance with waiver
provision, Silver Spring, MD, (1993).
5. Hearing Review, Annual Survey, June, (2000).
6. Becker, W., Naumann, H.H., and Pfaltz, C.R., Ear,
Nose and Throat Diseases, ed. Buckingham, R.A., New
York: Theime Medical Publishers, Inc., pp. 134-136,
(1989).
7. Jafek, B.W., Murrow, B.W., ENT Secrets, 2nd edition,
Philadelphia: Hanley & Belfus,Inc., pp. 55-56, (2001).
8. Doyle, T.N., and Hoffman, J.E., “General Medical
Considerations in Audiology”, Jack Katz, ed., Handbook
of Clinical Audiology, 3rd edition, Baltimore: Williams
& Wilkins, pp. 39-47, (1989)
9. Newby, H.A., and Popelka, G.R., Audiology, 5th
edition, Englewood Cliffs, NJ: Prentice-Hall, Inc., pp.
64-66, 71, (1985)
10. Chartrand, M.S., “Video Otoscopy Observations
Utilizing Miracell Botanicals”, Rye, CO: DigiCare
Hearing Research & Rehabilitation, (2002).
11. Davis, W.E., “The external and middle ear”, in
Otolaryngology-Head and Neck Surgery: Principles and
Concepts, Templar, J., and Dais, W.E., ed., St. Louis:
Ishiyaku EuroAmerica, Inc., pp. 34-36, (1987)
12. Wallach, J., Interpretation of Diagnostic Tests: A
Synopsis of Laboratory Medicine, 4th edition, Boston;
Little Brown & Company, (1986).
13. Fishman, M.C., Hoffman, A.R., Klauser, R.D., and
Thaler, M.S., Medicine, 4th ed., Philadelphia:
Lippincott-Raven, (1996).
14. Northern, J.L., and Downs, M.P., Hearing in
Children, 4th edition, Philadelphia: Lippincott Williams
& Wilkins, (1991). 15. Habif, T.P., Clinical
Dermatology, 2nd edition, St. Louis: C.V. Mosby Company,
pp. 28-31, (1990)
16. National Institutes of Health, Office of Medical
Allications Research, Consensus Statement on Acoustic
Neuroma, Vol. 9, No. 4, Bethesda, MD, 1991.
17. Chartrand, M.S., Hearing Instrument Counseling, 2nd
edition, Livonia, MI: International Institute for
Hearing Instruments Studies, pg. 106, (1999).
18. DeGowin, R.L, DeGowin & DeGowin’s Diagnostic
Examination, 5th ed., New York: MacMillan Publishing
Company, (1987).
19. Pulec, J., “Meniere’s Disease”, Hearing Disorders,
2nd edition, ed. Northern, J., Boston:Little, Brown, and
Company, (1984).
20. Chartrand, M.S. & Chartrand, G.A., Nuts & Bolts in
Hearing Aid Practice, continuing education course,
Livonia, MI: International Institute for Hearing
Instruments Studies, (2002).
21. Author’s discussion with two of the original 1977
FDA panel members regarding the intent of the hearing
aid rule at Tri-State Convention, Portland, OR, (1988).
Pathogenic Bacteria Lecture Questions
Host-Parasite interactions
1. What stages occur during the pathogenesis of a
microbial infection? Why is it important to understand
the mechanisms involved at each stage of infection by
any specific microbe? In order for a pathogen to
establish an infection, it must first gain access to the
host through contact and entry. It then establishes
itself (colonization). Once a colony is developing, the
infection spreads to other parts of the body. If the
organism is able to survive, it may begin to cause
damage (pathology) to the host.
To fight pathogenic organisms effectively, we must
understand each step of the development of pathology if
we want to block the orderly progression of an
infection.
2. What are the normal flora in each region of the body?
What factors modify the numbers and kinds of microbes in
the normal flora?
Site Normal Flora
Blood none
Tissue none
Skin staphylococci, propionibacterium
Mouth streptococci, neisseria, moraxella
Nasopharynx Staph aureus and those of mouth
Esophagus transient mouth flora
Stomach few (if any)
Small intestine scanty, variable
Large intestine Bifidobacterium, lactobacillus, strep
Vagina skin / colon flora
Several factors can modify the "normal"flora of any
organ system. The amount and type of nutrients
available, pH, redox potentials, local acting anti
microbials (bile, lysozyme, etc), and competition for
nutrients among bacteria all contribute to the selection
of the "normal" flora. As the host’s condition changes
with illness, pregnancy, age, or geographic location,
the "normal" flora will change. Some bacteria that are
"normal" in one site can cause disease in another. (ex:
E. coli in urinary tract-->infection)
3. For each model of microbial pathogenesis discussed in
lecture, what kind of virulence factors are important?
Virulence factors inherent to bacteria (whether found on
the chromosome, plasmid or in a bacteriophage) allow the
bacteria to survive in conditions that kill other
bacteria. The expression of these virulence factors is
tightly regulated in response to environmental stimuli.
Bacteria can mimic external signals that stimulate host
cells, secrete toxins that damage host cells, block the
release of neuromuscular signals, or inhibit host
protein synthesis.
4. For each model of microbial pathogenesis discussed in
lecture, what kind of microbial defenses are important
for the host?
The host defense against bacteria is a broad system.
Nonspecific and mechanical barriers such as the external
epithelial layer, flushing action of secretions, and a
hostile surface environment (lo pH, enzymes, etc) are
the first line of defense against pathogens. The immune
response mounted against pathogens that penetrate the
host is the second line of defense. People who cannot
mount a well rounded immune response are at much higher
risk of developing life threatening infections.
Bacterial Toxins
1. How would you investigate whether a newly discovered
pathogenic bacterium that causes pneumonia produces a
toxin that is essential for pathogenesis?
By using the molecular version of Koch’s postulates, one
could investigate the pathogenesis of a specific toxin
by the following sequence:
1. Clone the gene for the suspected toxin
2. Inactivate the cloned gene in vitro by genetic
engineering
3. Replace the wild type allele in the pathogenic
microbe with the inactivated allele
4. See if the loss of the suspected toxin results in
loss of pathogenesis
2. What are A-B type toxins? What are the functions of
the two domains or subunits of such toxins?
Toxins that must cross the plasma membrane of host cells
to reach an intracellular target are identified as A-B
type toxins. They are bifunctional proteins with
separate domains. The A domain is the "active" domain
and the B domain is the "binding" domain. The toxins use
normal membrane receptors as points of entry into the
cell and susceptibility is determined by the presence or
absence of the particular receptor on a specific cell.
Most toxis bind their receptor and are then transported,
by endocytosis, into the cytoplasm where they become
active and attack their target.
3. What features are shared by ADP-ribosylating toxins?
What features are unique for each toxin? What are some
possible reasons that many toxins have ADP-ribosylating
activity?
All of the ADP-ribosylating toxins catalyze the transfer
of ADP-ribose from NAD to acceptor proteins. the NAD
binding domain is highly cconserved among these toxins.
But, they recognize different acceptor proteins and
interact with target cells via defferent cell durface
receptors. One could postulate that the reason many
toxins use this mechanism is its effectiveness in
rendering the host defenseless and lead to the death of
the host cell. One could also postulate that the genetic
information for this toxin has been passed from species
to species over a long period of time and that each
bacteria has modified the toxin to fit its particular
needs.
4. How would you test for immunity to diptheria? To
tetanus?
One could inject a previously immunized person (either
one who has had an infection or one who has been
immunized) with a small amount of the toxoid from the
two diseases and see if an immune response develops. By
measuring the antibody titer to the disease, one could
quantitatively assess host immunity.
Enteric Bacteria
1. What is the purpose of culturing diarrheic stools
onto media containing lactose?
This would allow one to discern the types of bacteria
growing in a patients GI tract. Salmonella, Shigella,
and Yersinia are all nonfermenters of lactose. MacConkey
agar contains bile salts, lactose, dyes, nutrients and a
pH sensitive indicator. Bacteria that can ferment
lactose will produce acid, and cause the pH indicator to
become hot pink. Bacteria that are unable to ferment
lactose (Salmonella, Shigella, and Yersinia) will appear
as clear or colorless on the plate.
2. What is meant by endotoxin? Describe the effects of
such a molecule.
Endotoxin is the lipid A portion of LPS that causes
endotoxic shock upon release in the host circulation.
This presents as fever, intravascular coagulation,
hypotension, complement activation, and B cell
stimulation.
3. How are the enterobacteriacea serotyped? For what
purpose is this done?
The enterobacteriacea are serotyped by agglutination
with antisera to three different surface antigens (O, H
and K/Vi). The differences seen on serotyping allow one
to identify the bacterial species.
4. Compare the pathogenesis of Shigella sp. versus
Salmonella typhi. How does each pathogen interact with
macrophages? How does S. typhi disseminate thru the
body? What is the basis for the colonic ulcers that
occur during Shigella infection?
Shigella species passes thru the stomach and small
intestine, when it reaches the colon it interacts with
the M cell, an antigen presenting cell of Peyer’s
patches. It causes death of macrophages in the lamina
propria by inducing apoptosis. It is rarely disseminated
into the bloodstream. The bacterial invasion of the
colon results in acute inflammation and necrosis. This
leads to the formation of abcesses and ulcers.
S. typhi enters M cells by endocytosis and eventually
macrophages in the submucosal layer. These infected
macrophages escape the colonic structure and eventually
seed the bloodstream. Infections usually spread
systemically and come to a focus in the liver and
spleen.
5. Compare the reservoirs, infectious dose, and risk
groups for Shigella, Salmonella typhi, Salmonella
enteriditis, and Y. enterocolotica. Where in the world
are S. flexnerii, S. sonnei, and S. typhi isolated?
Bacteria Reservoir Infectious dose Hi risk group
Location
Shigella humans 200 institutions or crowding worlwide
S. sonnei humans 200 children US / 1st world
S. flexnerii humans 200 institutions or crowding
American Indians / 3rd world
Sal. typhi humans 106 children / elderly 3rd world
Sal. enteriditis animals 104 picnics worldwide
Y. enterocolitica animals >109 people who eat
undercooked meat Europe / Scandinavia
6. How might one prevent transmission of S. typhi,
Shigella and S. enterocolitica? For which of these
pathogens is there a vaccine?
All of these diseases can be prevented by practicing
improved sanitation and hygiene. Basic preventive
medicine measures can prevent these illnesses (hand
washing, latrines away from food prep sites, pest
control, etc). There is a vaccine against S. typhi.
7. Which of the enterobacteriaceae can cause mesenteric
lymphadenitis?
Yersinia sp. causes mesenteric lymphadenitis.
Enterics II
1. What are the different ways that E. Coli can cause
diarrhea and enteritis? Which bacteria use which
mechanism?
E. coli can cause diarrhea via several mechanisms. ETEC
produces heat labile and heat stable toxins that affect
the small bowel, producing a watery diarrhea without
blood. EIEC causes diarrhea identical to a Shigella
infection, bloody and loaded with neutrophils. EPEC
causes the "attaching and effacement" lesions that lead
to a watery diarrhea. EHEC causes bloody diarrhea
without WBCs in the stool.
2. What is the mechanism of heat labile toxin (LT),
stable toxin (ST), and Shiga toxin?
LT activates adenylate cyclase and cAMP in the
intestinal cell (this is identical to the action of
cholera toxin).
ST activates guanylate cyclase and cGMP in the
intestinal cell.
Shiga toxin is cytotoxic and enterotoxic. It inhibits
eukaryotic protein synthesis and has neurotoxic effects
as well.
3. Why are US travelers generally susceptible to ETEC
infection but not to EPEC infection?
EPEC infects susceptible people of all ages who are
exposed to the pathogen. EPEC only infects small
children, possibly due to selection of specific host
characteristics by the pathogen that are present in
infants, but not present in adults.
4. What is the natural habitat of Vibrio and
Campylobacter species? What are some common sources of
infection with these pathogens?
Vibrio is abundant in marine and surface waters.
Drinking water that is infested with the pathogen or
eating aquatic life from infested waters causes disease
in humans.
Campylobacter is a normal GI commensal of many animals.
Consumption of water that is infested with the pathogen
or eating animals contaminated with the pathogen causes
disease in humans.
5. Describe the spectrum of disease caused by Vibrio
Cholerae. Name two virulence factors utilized by this
pathogen and describe the physiological basis behind the
intestinal secretion caused by this organism.
Cholera can range from an asymptomatic "carrier" state
to full blown "cholera gravis" that is life threatening
due to the massive loss of fluid. The bacteria use a
specific pillus (Tcp) to attach to the brush border of
epithelial cells. The bacteria then produce the cholera
toxin that activates adenylate cyclase and increases the
intracellular cAMP level. This leads to increased
secretion of Cl-, K+ and HCO3- from cells and decreased
NaCl coupled absorption. The outward flow of ions from
the intestinal cells leads to an osmotic loss of water.
6. Where is cholera endemic? Who is at risk? What
vaccines are available?
Cholera is endemic to Indian, southern Asia, Africa,
Indonesia, South / Central America and the southern U.S.
coastline. Children in endemic areas are at greatest
risk of developing the disease. There is a parenteral
whole cell killed vaccine available that has some
drawbacks.
7. What is the first and formost important form of
treatment for a cholera patient?
Oral or IV fluid and electrolyte replacement is the most
important treatment of cholera.
8. Describe the type of stools that can result from
infection with Campylobacter jejuni. What are
the special conditions needed to culture this organism?
Stools from an infected person resemble those of a
person with Shigella. They can be bloody and contain
neutrophils. This organism must be cultured in CO2 and ¯
O2.
Enteric Bacteria III
1. Describe the pathogenesis of H. Pylori, including the
host response to infection. What are some of the major
virulence factors used by this pathogen?
H. pylori is ingested and passes into the stomach. It
penetrates the gastric mucosa and colonizes the
stomach’s epithelium. Damage to the epithelium leads to
superficial inflammation and is followed by deep
inflammation. The bacteria excrete urease that allows
the bacteria to survive in the low pH of the stomach.
The bacterial flagella may assist in the penetration of
the mucosa and a vacuolating cytotoxin may assist in
damaging cells.
2. Compare the epidemiology of H. Pylori infection among
people of the 1st and 3rd worlds. How is the infection
transmitted?
H. Pylori is found in the feces, oral cavity and dental
plaques of infected individuals. The disease is
transmitted by ingestion of the pathogen.
3. What clinical tests can one use to diagnose H. Pylori
infection?
Detection of urease in gastric biopsies can aid in the
diagnosis. Patients can be given radiolabeled urea and
the detection of radiolabeled CO2 on exhalation can also
assist in diagnosis.
4. Who is most susceptible to uncomplicated UTI? To
complicated UTI?
Uncomplicated UTIs occur in otherwise healthy people.
They are usually (80%) caused by E. coli. Complicated
UTIs are found in people who have urinary catheters, are
immunosuppressed, or have an anatomical or functional
defect that interferes with the normal voiding of urine.
5. What role does the urease produced by P. Mirabilis
play in urinary tract disease? How might lateral
flagella enable P. mirabilis to establish
pyelonephritis?
The urease produced by P. Mirabilis can lead to the
formation of kidney stones and subsequent blockage of
the urinary tract. The lateral flagella allow the
organism to swim upstream in the urinary tract and hold
on oncce they reach their site of colonization.
6. How are UTI diagnosed in the lab? What is the
importance of a "clean catch" specimen?
Urine specimens are collected after the stream of urine
has begun, and are then cultured. If bacteria are
isolated, a UTI is suspected. Presence of multiple
organisms may imply contamination.
7. Which members of the Enterobacteriaceae are common
contaminants of parenteral fluid?
Shigella, ETEC, EIEC, EHEC, Vibrio cholerae, and
Campylobacter jejuni are all potential contaminants of
parenteral fluids.
8. What is bacteremia? Sepsis? endotoxic shock?
Bacteremia is defined as the presence of viable bacteria
in the bloodstream. Sepsis is defined as the presence of
bacteria or toxic bacterial metabolites in the
bloodstream or tissues. Endotoxic shock is the systemic
reaction to an overwhelming presence of bacterial toxins
in the bloodstream.
9. What are the lab characteristics of Psuedomonas
aeruginosa? Where is it found in nature? How is it
transmitted?
Psuedomonas aeruginosa are aerobic, gram (-) rods that
are oxidase (+). They oxidize but do not ferment glucose
and posssess polar flagellum. The ar found ubiquitous in
nature and are transmitted in fluid media. They cause
opportunisitic infections in patients with compromised
inate immunity (surgical wounds, trauma, eye injury, IV
catheters, patients with sepsis).
10. How might the polysaccharide capsule of K.
pneumoniae assist in establishing infection? What is
responsible for the mucoid appearance of Psuedomonas
aeruginosa isolates in CF patients?
The polysaccharide capsule of K. pneumoniae assists the
organism in establishing infections by inhibiting the
actions of host immune responses and antimicrobial
agents. The mucoid appearance in CF patient is due to
the production of and alginate capsule that is very
"sticky."
11. What is the mechanism of action of Psuedomonas
aeruginosa exotoxin A?
Psuedomonas aeruginosa exotoxin A is a potent inhibitor
of mammalian protein synthesis. Its mechanism is
identical to diptheria toxin, in that it ADP-ribosylates
EF-2 and prevent protein synthesis.
Anaerobes
1. Compare and contrast the mode of action of botulinus
toxin and tetanospasmin.
Botulinum toxin interferes with the release of
acetylcholine at the neuromuscular junction by cleaving
components of the neurosecretory apparatus ® flaccid
paralysis.
Tetanus toxin (tetanospasmin) cleaves vAMP and prevents
the release of glycine from inhibitory interneurons in
the spinal cord ® spastic paralysis.
2. What is infant botulism? What are the proposed
mechanisms of pathogenesis?
Infant botulism occurs when the infant’s gut is
colonized by C. botulinum that produces toxin in vivo.
This leads to generalized hypotonia ® "floppy baby"
syndrome.
3. Which of the organisms discussed are gram positive,
spore forming anaerobes? Gram negative anaerobes? Gram
positive anaerobes?
The clostridia species are gram-pos spore forming rods.
Bacteroides species are gram-neg obligate anaerobic
bacillus. Bacillus anthracis is an aerobic, gram
positive rod.
4. What are the primary virulence determinants of B.
Anthracis?
Virulent strains of Bacillus anthracis produce an
anti-phagocytic poly D-glutamic acid capsule that
increases its ability to survive in the host. They also
produce three separate proteins (EF, LF, and PA) that
combine to form a toxin. Edema factor (EF) is a
calmodulin dependent bacterial adenylate cyclase. Lethal
factor (LF) has no known enzymatic activity. Protective
antigen (PA) is a tissue binding component required for
significant disease in the infected host.
5. How is tetanus prevented? How is botulism prevented?
Vaccination with tetanus toxoid causes the host to
produce protective antibodies for the disease. Botulism
is prevented by using a trivalent antitixon vaccine and
by proper food handling and preparation techniques.
6. How does C. perfringens alpha toxin work?
C. perfringens alpha toxin is a lecithinase that causes
hemolysis of the RBC in circulation, destroys platelets
and causes widespread damage.
7. Discuss the pathogenesis of botulism,
pseudomembranous colitis and C. perfringens food
poisoning.
Botulism, pseudomembranous colitis and C. perfringens
food poisoning are all similar in that they involve
ingestion of vegatative cells or spores. The cells or
spores undre anaerobic conditions in the gut mature to
produce an enterotoxin that has either systemic or local
effects.
8. What is the most common bacterial species in the
human gut?
Bacteroides spp.
9. What is the "preeminent" anaerobic pathogen in
humans?
Bacteroides fragilis is the preeminent anaerobic
pathogen in humans. This is based on virulence, ubiquity
in various sites, and resistance to antimicrobials. It
causes abcesses and tissue destruction on a regular
basis.
Staphylococci
1. Which species of Staphylococci are medically relevant
to human disease?
S. Aureus, S. epidermidis and S. saprophyticus are
medically relavant to humans.
2. How are S. Aureus infections acquired? What are some
of the risk groups for S. aureus invasive disease?
Most infections of staphylococci occur from
autoinfection of strains that reside on the skin and
mucous membranes (nose, perineum and urinary tract).
Patients whose innate immunity has been compromised are
at increased risk for developing invasive S. aureus
infection. Patients who are diabetic, elderly,
alcoholic, abuse IV drugs, have cystic fibrosis and
those with indwelling catheters are at increased risk.
Surgical patients and others who have open wounds are
also at increased risk.
3. Describe the toxins produced by S. aureus. What other
virulence factors are important in S. aureus disease?
I. Toxins
-Heat stable enterotoxin------------------->food
poisoning
-Exfoliatin---------------------------------->scalded
skin syndrome
-TSST-1----------------------------------->Toxic shock
syndrome
-Alpha hemolysin (a -toxin)------------->RBC lysis
II. Extracellular products
-Coagulase--------------->causes clot that walls off
bacteria from bloodstream
-Leukocidin------------->permeabilizes and kills PMNs
and macrophages
-Hyaluronidase--------->hydrolizes host extracellular
matrix and allows organism to move
III. Surface components
-Peptidoglycan layer---------------->septic shock
-Ribitol-techoic acid---------------->antigenic and
binds fibronectin
-Protein A--------------------------->binds Fc portion
of IgG --->antiphagocytic activity
-Clumping factor------------------->fibrinogen binding
receptor
-Cell surface bound coagulase---->causes bacteria to be
coated with fibrin and ¯ phagocytosis
4. How does one distinguish Staph species from Strep
species in the lab?
The catalase test distinguishes Staph species from Strep
species in the lab by testing the ability (inherent
enzymatic machinery) of the bacteria to catalyze the
reaction H2O2®H2O + O2. The enzyme required is
"catalase." Staph species are catalse (+) and strep
species are catalase (-).
5. What are some epidemiological tools used to study
Staph epidemics?
Bacteriophage typing is based on the fact that staph
species are lysogenic and carry phages to which they are
immune but that are lytic for other species. Plasmid
profiles allow one to characterize genetic info carried
on plasmids (antibiotic resistance, etc). DNA
fingerprinting can also be used to characterize the
genetic info in a given strain and compare it to other
strains.
6. How do Staph acquire antibiotic resistance? What is
signified by MRSA? What are the public health
implication of vancomycin resistant S. aureus isolates?
Penicillin resistance (and sometimes erythromycin) is
due to a b -lactamase that is coded on a staph plasmid.
Other low molecular weight plasmids encode resistance to
tetracycline, chloramphenicol and kanamycin. Methycillin
resistant staph aureus (MRSA) resistance to antibiotics
is coded for in the bacterial chromosome. Emerging
vancomycin resistance is probably due to genetic
transfer from Enterococcus species.
7. What type of infection do S. epidermis and S.
saprophyticus cause? How does one distinguish these
species from S. aureus in the lab?
S. epidermis causes nosocomial infections in patients
with indwelling catheters and prosthetic devices. S.
saprophyticus is responsible for 10-20% of primary UTI
in females. S. epidermis and S. saprophyticus are
coagulase (-) and can therefore be distinguished from
coagulase (+) S. Aureus in the lab.
Streptococci
1. What are the major virulence determinants for Strep
pneumoniae? Strep pyogenes? What immune mechanisms
protect the host against these organisms?
The most important virulence factors for Strep
pneumoniae are the capsular polysaccharides. They are
antigenic, anti-phagocytic, and a loss of the capsule
leads to a loss of virulence. Strep pneumoniae also
produce pneumolysin that injures pulmonary endothelial
cells.
The most important virulence factor for Strep pyogenes
is the production of M protein. It binds to the host
epidermis and is anti-phagocytic. The capsule of this
organism also contains hyaluronic acid that prevents the
host from attacking it (would lead to autoimmune
response to host tissue).
Humoral immunity (opsonization, phagocytosis, and
development of an antibody titer) are the most important
factors in protection for the host.
2. What are the primary disease caused by Strep
pyogenes? Strep pneumoniae? Strep agalactiae? Group D
streptococci? Viridans (a -hemolytic) strep?
Strep pyogenes (group
A)----------------------->impetigo, wound infections,
pharynigitis, cellulitis, necrotizing fascitis,
myositis, rhuematic fever
Strep
pneumoniae-------------------------------->pneumonia
Strep agalactiae (group B)--------------------->neonatal
meningitis
Group D streptococci--------------------------->UTI,
bacteremia (post urologic surg), endocarditis,
wound infection
Viridans (a -hemolytic)
strep------------------->endocarditis, dental caries
3. What are the morphologic and physiological
characteristics of all streptococci? In the clinical
lab, how would you distinguish Strep pneumoniae from
viridans (a -hemolytic) strep?
All streptococci species are gram (+) spheres that grow
in pairs or chains. They are non-motile and are catalase
(-).
In the clinical lab one could distinguish Strep
pneumoniae from viridans (a -hemolytic) strep based
on the fact that Strep pneumoniae is optochin sensitive
and viridans strep is not. Furthermore, viridans will
not grow in 6.5% NaCl/bile esculin.
4. Why is it clinically important to distinguish the
enterococci from other group D streptococci?
Enterococci share many characteristics with other group
D streptococci and are normal flora on the skin and in
the GI tract. Enterococci that move to other sites in
the body often cause disease (UTI, bacteremia,
endocarditis, wound infection) and may exhibit strong
antibiotic resistance. The other group D streptococci
are normally non-virulent and display very little
antimicrobial resistance.
5. Describe the extracellular and cell-associated
products of Streptococcus pyogenes. How are these
products used in the diagnosis of group A strep
infections?
One can purchase commercially antibodies to group A
strep that are linked to a staph species via protein A.
When this combination is added to a group A strep
sample, agglutination occurs. This confirms the presence
of the group A strep.
Group A strep also render a (+) PYR (pyrrolidonyl
arylamidase) test.
Neisseria I
1. What are the major virulence determinants of
meningococci? What are the primary host defense
mechanisms against these organisms?
The meningococci are obligate extracellular parasites.
They cannot survive inside PMNs. The meningococcal
capsule is antiphagocytic and is the major virulence
determinant.
The host defense mechanism against meningococci is
primarily a humoral response.
2. How would you isolate and identify N. meningitidis in
the clinical lab? How would you distinguish it from
normal flora neisseria?
Neisseria in general are gram (-) cocci that occur in
pairs. They are non-motile and are non-spore forming.
Pathogenic species will not grow at 220 C or on a growth
agar without blood. They do require 5-10% CO2 for
optimal growth. Non-pathogenic species grow well at 220
C or on a growth agar without blood. They do not require
5-10% CO2 for optimal growth.
3. What are the most common causes of bacterial
meningitis by age in the US?
Age #1 #2 #3 #4 #5
<1 month group B strep listeria monocyt strep pneum
1-23 months strep pneum neisseria menin group B strep
haemophilus flu
2-18 yrs neisseria menin strep pneum haemophilus flu
group B strep listeria monocyt
19-59 yrs strep pneum neisseria menin haemophilus flu
listeria monocyt group B strep
>60 yrs strep pneum listeria monocyt neisseria menin
haemophilus flu group B strep
4. Compare and contrast the meningococcal vaccines with
the pnuemococcal vaccines (Who gets them? How effective
are they? etc).
The meningococcal vaccine is available with A, C, Y and
W-135 capsular polysaccharides. It is not a good
immunogen for children >2 yrs of age. There is no group
B vaccine as yet because the capsular polysaccharide is
a poor immunogen even for adults.
The pneumococcal vaccine contains polysaccharide from
each of the 23 serotypes. It is also better for patients
that are >2 yrs of age. It is highly recommended for
people at hi risk® elderly , immune deficiency, chronic
disease patients, sickle cell anemia, splenectomized,
alcoholics.
Neisseria II
1. How does uncomplicated gonorrhea usually manifest in
a male? In a female of reproductive age? In a
pre-adolescent female?
Uncomplicated gonorrhea in a male is characterized by
urethritis. The patient will present with frequent,
urgent and painful urination. A yellow, mucopurulent
discharge containing neutrophils and gram (-) diplococci
is seen. The incubation period is 2-7 days after contact
with an infected partner.
Uncomplicated gonorrhea in a female of reproductive age
is characterized by cervicitis. This is an inflammation
of the endocervical canal epithelium. A mucopurulent
discharge is often seen. Bartholin’s glands can also
become infected and develop into an abcess.
Uncomplicated gonorrhea in a pre-adolescent female is
characterized by vulvovaginitis.
2. What are the clinical manifestations of ascended
reproductive tract infection in males and in females?
What post-infection complications might result?
Ascended reproductive tract infection in males can lead
to epididymitis and prostitis. Endometritis, salpingitis
and pelvic inflammatory disease are common in females
with an ascended infection. These infections all can
lead to sterility if severe and/or untreated. They can
also lead to ectopic pregnancy in women.
3. What other organisms cause acute urethritis in men
and urethritis / cervicitis in women? How would you
differentially diagnose these agents?
Chlamydia trachomatis, ureaplasma urealyticum,
trichomonas vaginalis and Herpes Simplex Virus all cause
urethritis in men and women. The diagnosis of the
causative agent in a given case is based on a gram-stain
of a sample taken from the patient. One should attempt
to grow pathogens on culture, conduct antibody titer
count and examine genomic information in order to form a
definitive diagnosis.
4. How would you isolate and identify N. gonorrhea in
the clinical laboratory? How would you distinguish it
from N.meningitidis?
First, one obtains a specimen from the patient. This can
be done by swabbing the infected site (urethra, cervix,
anus, etc.). Organisms are then cultured and classified.
N. gonorrhea are gram (-) diplococci, oxidase (+) and
nonmotile.
N. meningitidis is also gram (-) and grows on maltose.
N. gonorrhea grows on glucose but not maltose.
5. Discuss the evolution and mechanisms of gonococcal
resistance to penicillin. What other antimicrobial
agents are used to treat gonorrhea? Has resistance
developed to these agents? What are the mechanisms of
gonococcal resistance to these agents?
Gonococcal resistance to penicillin is carried on a
small plasmid. This genetic information for production
of a penicillinase was probably acquired from H.
ducreyi. Resistance can also occur in the form of
altered penicillin binding proteins that are
chromosomally encoded.
Tetracycline is also used to treat gonococcal infection,
but genetic information can transfer such that the
penicillin resistance also affects sensitivity to
tetracycline. This leads to a double resistant organism.
Fluoroquinolone treatment is effective, but resistance
is developing due to an altered DNA gyrase.
6. Which surface components of the gonococcus undergo
phase and antigenic variation?
The pili, opacity proteins, and the lipooligosaccharides
undergo phase and antigenic variation.
7. What are the epidemiological implications of phase
and antigenic variation of the gonococcal pili?
Because the outer pili of the gonococcal species are
highly variable, it is very difficult to design a
vaccine that can target a conserved structure. N.
gonorrhea do not possess a capsule and this also
increases the difficulty in developing a vaccine.
Mycobacterial infections
1. How is the cell mediated immune (CMI) response
involved in mycobacterial infection?
A host infected with mycobacteria fights the organism
through activated macrophages that kills the infectious
agent. CD4+ T-cells secrete lymphokines that activate
the macrophages. CD8+ T-cells release bacilli from
unactivated phagocytes and allow the organisms to be
ingested by activated macrophages. Patients who have
AIDS are at increased risk of developing mycobacterium
tuberculosis infection because they are CD4+ deficient
and cannot fight off the pathogen.
2. What characteristics of tuberculosis and leprosy are
important when considering the epidemiology of these
diseases?
Tuberculosis is a significant disease in the grand
scheme. Worldwide, there are 5-8 million new cases per
year and 2-3 million deaths. The concentration of TB is
increased in areas of poverty, overcrowding and
generally poor living conditions. TB is developing
significant resistance to antibiotic therapy. Less than
10 viable bacilli in the airway of a susceptable host
can cause disease. Because TB declined continuously for
several years, public awareness of the disease waned. As
TB reemerges as a resistant infectious agent, large
scale epidemics could occur.
There are 12 million cases of leprosy worldwide. Unlike
TB, a large dose of bacilli is required to cause
infection in a susceptable host. Leprosy is sensitive to
dapsone, but resistant strains are present.
3. Compare and contrast the two polar forms of leprosy.
Tuberculoid leprosy elicits a highly specific CMI
response. Bacilli in this form of the disease growin the
skin, but they also invade Schwann cell and macrophages
that can lead to peripheral neuropathy.The host is able
to kill (CD4+ T-cells) the bacilli and granulomas form
around sites of dermal infection.
Patients who develop lepromatous leprosy are deficient
in cell mediated immunity. Growth of the pathogen
proceeds relatively unimpeded (unless the patient is
treated with medication) and is spread via the host’s
lymphatic system. Skin lesions are extensive,
symmetrical, and diffuse. The face, lips, forehead, ears
and nose are the most common sites of infectious
lesions. Damage from this form of the disease is often
disfiguring and irreversible.
Corynebacteria and listeria
1. How would you process a clinical specimen to identify
C. diptheria? What properties distinguish it from Staph
Aureus and from Strep pneumoniae?
C. diptheria produces grey to black colonies on
selective medium that contains tellurite. It is an
aerobic, gram (+) rod that is not spore forming and is
catalase (+). Staph aureus and Strep pneumoniae are gram
(+) cocci. Staph aureus is catalase (+) and Strep
pneumoniae is catalase (-).
2. How do the properties of the A and B domains of
diptheria toxin contribute to its mode of action in
intoxicating susceptible human cells?
Diptheria toxin is secreted as a single polypeptide that
is proccessed by proteolysis into two subunits. Fragment
B binds to receptors on the plasma membrane of
susceptible cells and initiates uptake of the toxin by
receptor mediated endocytosis. Fragment A is transported
to the cytosol where it ADP-ribosylates EF2 and inhibits
protein synthesis by the infected cell. This reaction is
virtually identical to the pathogenic toxin of
psuedomonas aeruginosa but the two toxins recognize
different receptors.
3. What are the roles of antitoxic antibodies in
treatment and prevention of diptheria?
Antitoxic antibodies neutralize the toxicity of
diptheria toxin. Usually, a person who is suspected or
confirmed to have a case of diptheria is given horse
antitoxin. One can also be vaccinated against diptheria
and prevent infection by the use of the diphteria toxoid
immunization that is available.
4. What environmental and host factors predispose to
infection by Listeria monocytogenes? How would you
distinguish Listeria monocytogenes in a cultured
clinical specimen from Streptococcus penumoniae or from
Corynebacterium diptheria?
Persons who are HIV (+) and/or are immunosuppresed are
at increased risk of infection from Listeria. Most
infections in humans are food borne, but infection of a
pregnant woman can lead to abortion, stillbirth, and
transplacental infection of the infant.
Listeria monocytogenes is a short, gram (+) rod that is
non-sporulating, aerobic to microaerophilic and is
catalase (+). Strep pneumoniae is a gram (+) cocci that
is catalase (-). Corynebacterium diptheria produces grey
to black colonies on selective medium that contains
tellurite. It is an aerobic, gram (+) rod that is not
spore forming and is catalase (+).
Haemophilus, Moraxella and Bordetella
1. What are the primary virulence determinants of
Haemophilus influenzae? Bordetella pertussis? What
immune mechanisms are important in defense against these
organisms?
The primary virulence determinant of Haemophilus
influenzae is a capsular polysaccharide that is
antiphagocytic. Non-encapsulated forms are normal flora
of the URT that can cause some diseases (otitis media,
sinusitis, conjunctivitis, etc).
The primary virulence determinants of Bordetella
pertussis are toxins. The primary toxin activates the
mebrane adenylate cyclaase of eukaryotic cells via
ADP-ribosylation of regulatory protein G1. This leads to
an increase in cAMP and increased fluid secretion in the
URT. Bordetella pertussis also produces adhesive factors
and a tracheal cytotoxin.
Anti-capsular antibodies (humoral immunity) against
Haemophilus influenzae are protective. They coat the
pathogen and mediate complemtn dependent phagocytosis /
lysis.
Protection against Bordetella pertussis is somewhat
elusive. Antibodies are produced during active infection
with the disease and from immunization. Naturally
acquired immunity is not lifelong, second attacks are
common. Newborns and infants that are not immunized are
highly susceptible, reflecting a low level of antibody
being passed from the adult mother to the newborn child.
2. What are the in vitro growth requirements for H.
influenzae? How do these compare with H. ducreyi? B.
pertussis?
Haemophilus influenze requires X (hemin, heat stable) or
V (can be replaced by NAD / NADP, heat labile). These
factors are provided by chocolate agar. The organism
grows best in 5-10% CO2.
Heamophilus ducreyi also grows best on enriched
chocolate agar in 10% CO2 and at 350 C.
Bordatella pertussis requires enriched media that binds
fatty acids. Bordet-Gengou agar (contains potato
extract, 30% blood and glycerol) is ideal.
3. What is the chemical composition of the type b
capsule? How does this compare with the capsule of S.
pneumoniae? B. anthracis? E. coli K-1?
The Haemophilus influenzae type b capsule is composed of
polyribose-ribitol phosphate (PRP).
The capsule of S. pneumoniae is composed of a very
diverse group of polysaccharides, choline, acetyl, and
phosphate groups. Over 80 different combinations have
been classified.
The capsule of Bacillus anthracis is D-glutamic acid
polypeptide.
E. coli K-1 species produce a capsular polysaccharide
that contains sialic acid and is structurally identical
to the group B polysaccharide of Neisseria meningitidis.
4. What are the similarities and differences in mode of
action of cholera toxin, diptheria toxin, and pertussis
toxin?
Cholera toxin, diptheria toxin and pertussis toxin are
all ADP-ribosylases. Their most significant difference
is their target. Cholera toxin affects the stimulatory G
protein (GS)of the adenylate cyclase complex. Pertussis
toxin attacks the inhibitory protein (GI) of the same
complex. Diptheria toxin affects elongation factor 2
(EF2) that leads to a blockage of host cell protein
synthesis.
5. Compare the vaccines against pertussis and H.
influenzae type b with regard to composition and
efficacy.
The current pertussis vaccine is composed of a mixture
of purified, inactivated B. pertussis products. It is
very effective in producing immunity to the disease and
has only local side effects.
The H. influenzae type b (Hib) vaccine is a conjugation
of Hib with diptheria toxoid. It is highly effective and
serves as a model for the development of future
vaccines.
6. How does B. pertussis colonize the respiratory tract?
Is it an invasive organism? How does the
pathogenesis of pertussis compare with that of
diptheria? Cholera?
B. pertussis colonizes the ciliated bronchial epithelium
without invading the tissue. It does this via
filamentous attachment. The bacteria first attach to and
immobilize the cilia. The ciliated epithelial cells are
then slowly destroyed by bacterial toxins.
The diseases caused by infection with Vibrio cholera and
corynebacteria diptheriae are due to the production of
ADP-robosylating toxins by the organism that lead to
altered host cell function.
Mycoplasma and legionella infections
1. How do mycoplasms differ from other bacteria? What
characteristics do they have in common? How do these
organisms appear under a microscope?
Mycoplasm do not have a cell wall. They are much smaller
than other bacteria, and contain DNA genomes. Under a
microscope, mycoplasm stain poorly or not at all and
because of their small size, they are difficult to see.
2. What are the major disease syndromes caused by
mycoplasma? What pathogenic mechanisms are involved?
Mycoplasma pneumonia causes primary atypical pneumonia
(walking pneumonia). Mycoplasma hominis causes genital
infections. Many other clinical syndromes (wheezing,
pharyngitis, rhinitis, erythema multiforme, myringitis,
otitis media, et al) are associated with mycoplasma
infection.
Mycoplasma enter the respiratory tract via inhalation
and attach to cells in the lower part of the tract. The
pathogens remain extracellular and intefere with ciliary
action. The immune response to infection may lead to an
autoimmune attack on the host in some cases.
3. What are the most common clinical signs of infection
with M. pnuemoniae?
One sees non-specific pulmonary infiltrates, fever,
malaise, myalgia, sore throat, and cough (nonproductive,
productive, or paroxysmal).
4. Why do you think that Legionella pneumoniae was not
discovered until the mid 1970’s? What are its
characteristic properties?
Legionella pneumoniae is a motile, gram (-) rod that is
difficult to stain. It is very difficult to culture due
to restrictive growth criteria (requires cysteine and
iron). Because it is very small (.5-.7mm wide and 2-20mm
long) and difficult to stain, isolation and
identification is very difficult.
5. What are some ecological niches for L. pneumoniae?
How is it transmitted?
Legionella pneumoniae hides in air conditioning
equipment that uses water internally (cooling towers and
condensers). Shower heads, faucet taps, and vegetable
misters can also harbor the organism.
The pathogen is transmitted by inhalation of the
aerosolized bacteria. It is not easily (if at all)
spread from person to person.
6. How is legionellosis diagnosed in the lab?
Demonstration in culture of the bacteria taken from
tissue or secretions is useful for diagnosis. Bacteria
can be demonstrated in tissue by using a silver
impregnation technique that highlights the intracellular
pathogen. Direct immunofluorescence can detect the
organism in pleural fluid or lung tissue. A 4-fold rise
in the antibody titer of a suspected patient is strong
evidence for infection.
Chlamydial infections
1. Why are chlamydial infections often misdiagnosed?
Chlamydial infection can range from a chronic /
persistent infection to acute infection, or totally
inapparent to the host. The symptoms of chlamydial
infection are common to many other STDs. Microscopic
examination of specimens in an attempt to identify the
organism is very difficult because of the size of the
pathogen. Growing these organisms in culture is very
difficult. The diagnosis of chlamydia is usually made
when a patient presents with symptoms of STD and no
gonococci can be demonstrated in a specimen. Many times,
an infection with gonococci masks an infection with
chlamydia.
2. Why are chlamydial infections often inappropriately
treated?
Because chlamydia is difficult to diagnose, treatment
for the patient’s symptoms can be ineffective against
the pathogen. If one treats for a gonococci infection
without including antimicrobials against chlamydia, the
infection may not be cleared by the host.
3. How would you interrupt the cycle of transmission of
trachoma? Nongonococcal urethritis? Psittacosis?
Lymphogranuloma venereum?
4. How do reticulate bodies (Rbs) differ from elementary
bodies (Ebs)?
EB RB
Morphology small and dense large, homogenous
Size .25 mm .6-1.0 mm
Stage extracellular/infectious intracellular/replicative
Osmotic fragility --- +++
Metabolic activity --- +++
Outer membrane cross-linked not cross-linked
5. What antibiotics are most effective in treating
chlamydial infections? Why?
Doxycycline (tetracycline) is the anitbiotic of choice.
Chlamydia do not possess a peptidoglycan layer in their
cell membrane. Therefore, antibiotics directed toward
cell wall synthesis are ineffective. Chlamydia is an
intracellular pathogen and tetracycline is effective
against it because the drug is very hydrophobic. This
decreases its ability to enter and attack host cells.
However, once inside the host cell the drug is actively
taken up by the pathogen whose ribosomes are very
sensitive to its action.
Spirochetes
1. What features do all spirochetes have in common? What
features distinguish the genera Treponema, Borrelia and
Leptospira?
Spirochetes are spiral shaped organisms that don’t gram
stain. They are also very difficult to culture in vitro.
The periodicity of the coil and the overall size of the
organism varies among the genera and species in the
spirochete family. Spirochetes are prokaryotes with
inner and outer membranes. They also display corkscrew
motility.
Treponema are 5 to 15 mm in length with regular spirals
1mm in length and an amplitude of .3 mm.
Borellia is a large spirochete 10 to 30m m long and .3 m
m wide. It contains 15 to 20 axial flagella. The spirals
are irregular with a 2 to 4 m m wavelength.
Leptospira is a slim (.15m m) spirochete 5-15 m m long.
It displays a single axial filament, fine closely wound
sprials, and hooked ends.
2. What are the clinical stages of syphillis? Where are
the organisms located during each stage? What are the
host responses to infection at each stage? How is the
diagnosis of syphillis established by lab tests?
10 syphillis presents with a hard, painless genital
chancre that is teeming with infective organisms.
Patients in this phase are at increased risk of
spreading HIV. Lymphocytes, monocytes and plasma cells
surround the lesion. The chancre heals spontaneously but
systemic infection remains.
20 syphillis presents with papulosquamous rashes on the
soles, palms, and mucous mebranes. Painless, mucosal
warty lesions in the perineal and genital area, known as
condyloma lata, is seen in this stage. Regional
adenopathy and tenderness may be present.
Latent syphillis is an asymptomatic infection (carrier).
30 syphillis appears as early as 5 years, and as late as
20 years, after the initial infection. Patients present
with syphilitic aortitis, CNS effects, and gummas | | | | |
