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MICROBIOLOGY & IMMUNOLOGY
FINAL EXAM ON OCULAR MICROBIOLOGY
Dr. William J. Benjamin
1:00 pm – 3:00 pm, Tuesday, November 11, 2008 in HPB 301 & 303
NAME: ______Score: ______/ 188
Part A: Select the single most appropriate answer for questions 1 to 63. Each
question is worth 2 points.
1. Mycobacteria can be seen by light microscopy as beaded red rods after they have been
stained with:
A. Gram stain
B. Acid-Fast stain
C. Wood stain
D. Giemsa stain
E. Finishing stain
2. A person’s eyes came into contact with some cotton dust while working on a farm. He
is in your office 3 days after the incident and has developed a keratoconjunctivitis with a
macular keratitis on the left eye. You should not prescribe or use the following at this
point:
A. A topical corticosteroid drop.
B. A topical anti-bacterial drop.
C. A topical anti-fungal drop.
C. An oral anti-bacterial preparation.
E. A bandage soft contact lens.
3. A product that has been recommended for use in cases of Epidemic Keratoconjunctivitis is?
A. Steri-Lid Eyelid Cleanser
B. Dove Dishwashing Liquid
C. Alcon Betadine 5% Ophthalmic Prep Solution
D. OcuSoft Lid Scrub Plus
E. Johnson & Johnson Baby Shampoo
4. It is best, all other things being equal, to prescribe an ophthalmic antibiotic that has the
following characteristic:
A. It is well-known as an antibiotic used for respiratory infections.
B. It is not used much for infections or conditions elsewhere in the body.
C. It has a very high MIC.
D. It has a very high MBC.
E. It is generally not commercially available in ophthalmic preparations.
5. The standardized agar used to perform disc diffusion susceptibility testing for
Haemophilus influenzae, as opposed to most other pathogens, is:
A. Mueller-Hinton agar
B. Chocolate agar
C. Sabouraud's agar with or without an antibacterial
D. Mueller-Hinton agar with 5% sheep’s blood
E. Mueller-Hinton agar with 5% sheep’s blood, chocolated
6. The nematode most associated with chorioretinitis lesions of the ocular posterior pole
in humans is:
A. Candida albicans
B. Toxocara canis
C. Histoplasma capsulatum
D. Aspergillis fumigatus
E. Toxoplasma gondii
7. You prescribed treatment for a farm laborer having a macular keratitis with a topical
anti-bacterial drop containing gatifloxacin, a relatively new fluoroquinolone. He had had
some hay blown into his eyes 3 days beforehand. Two days after initiation of your
treatment the lesion appeared marginally better but the patient’s photophobia and eye
irritation had only slightly diminished. You should consider that:
A. The infecting agent could be a bacterium that is resistant to the anti-bacterial
being used.
B. The infecting agent could be a mycobacterium that is resistant to the antibacterial
being used.
C. The infecting agent could be a fungus that is resistant to the anti-bacterial
being used.
D. The infecting agent could be a parasite that is resistant to the anti-bacterial
being used.
E. Any of the above could be true.
8. You prescribed treatment for a soft contact lens wearer having a keratoconjunctivitis
accompanied by purulence. Wear of contact lenses was discontinued and the patient used
tobramycin ophthalmic drops t.i.d. for 2 days. The condition at that time appeared to be
resolving and, 5 days later (1 week after the initial visit), the condition looked resolved.
You asked the patient to keep on the drops for 3 more days and taper off, then to resume
contact lens wear with new lenses, storage cases, and solutions 2 weeks after the original
visit. The patient came back at that time (2 weeks after the initial visit) with an angry
looking keratoconjunctivitis in the same eye. You should consider that:
A. The patient may not have complied with your request by discontinuing the
antibacterial drops too early. Resistant strains of the infecting agent had
not been eliminated and the infection came back.
B. A pathogen came in contact with the eye after the antibacterial drops had been
discontinued but before the normal flora were able to re-establish. Another
infection formed quickly in this environment.
C. The patient may not have complied with your request to restart contact lens
wear using new lenses, new cases, and/or new solutions. The eye was
infected again by the agent that had caused the original infection.
D. The new infection may have no relationship to the previous infection or its
treatment.
E. Any of the above could be true.
9. Fungal infections of the eye are associated with:
A. Immunocompromised persons.
B. Ocular trauma.
C. Ocular contamination with vegetable matter.
D. Superinfection.
E. All of the above have an association with fungal eye infections.
10. The following is the only topical agent known as an antifungal that is commercially
available by prescription in an ophthalmic preparation:
A. Tobramycin
B. Prednisolone
C. Amphotericin B
D. Natamycin
E. Zymar
11. Two bacterial ocular pathogens that apparently have a special affinity for corneal
epithelial cells are:
A. Pseudomonas aeruginosa and Streptococcus pneumoniae
B. Chlamydia trachomatis and Herpes simplex
C. Staphylococcus aureus and Corynebacterium diphtheriae
D. Serratia marcescens and Streptococcus pyogenes
E. Moraxella lacunata and Haemophilis influenzae
12. An intracellular parasite known to cause ocular fundus (chorioretinal) lesions similar
to, but generally distinguishable from, those of Histoplasma capsulatum is:
A. Toxocara canis
B. Toxoplasma gondii
C. Acanthamoeba sp.
D. Leishmania sp.
E. Microsporidia
13. In the early stages, keratitis caused by Acanthamoeba is often mistaken for keratitis
caused by:
A. Toxocara canis
B. Pseudomonas aeruginosa
C. Adenovirus
D. Microsporidia
E. Herpes-like viruses
14. Cytology of a conjunctival scrape for an eye having signs and symptoms of ocular
inflammation is polynuclear, showing only many polymorphonuclear cells. The
patient’s contact lenses have small deposits with feathered edges, indicative of
hyphae. Without consideration of any other signs and symptoms, the most likely
diagnosis for this eye is:
A. Bacterial infection
B. Fungal infection
C. Chlamydial infection
D. Viral infection
E. Protozoan infection
15. Cytology of a conjunctival scrape for an eye having signs and symptoms of ocular
inflammation is eosinophilic: you see a few eosinophils. Without consideration of
the signs and symptoms, the most likely diagnosis for this eye is:
A. Bacterial infection
B. Fungal infection
C. Chlamydial infection
D. Viral infection
E. Immunologic/Allergenic inflammation
16. When treating an eye with a topical antibiotic, the patient should nearly always finish
the entire amount of drug, either 10 or 14 days depending on the Rx, primarily since:
A. To allow the eye to counteract toxic or allergenic side effects of drug.
B. To more effectively kill opportunistic organisms not as influenced by the drug.
C. To kill off the normal flora in order to aseptisize the affected area.
D. To allow more time to kill resistant strains of the pathogenic organism.
E. To disrupt the corneal epithelium so as to get more drug into the cornea.
17. These are pathogenic extracellular protozoans or multi-cellular parasites except:
A. Trypanosoma sp.
B. Malassezia furfur
C. Toxocara canis
D. Onchocerca volvulus
E. Thelazia sp.
18. Epsilometer susceptibility tests are performed with filter paper strips impregnated
with various antibiotic substances on a particular type of agar plate evenly streaked with
the bacterium strain to be tested. Which medium is the standard used in most cases?
A. Chocolate agar
B. Mueller-Hinton agar
C. Mueller-Hinton agar with 5% sheep’s blood
D. Chocolated Mueller-Hinton agar
E. Sabouraud's agar with or without antibiotic
19. The standardized agar used to perform disc diffusion susceptibility testing for
Streptococcus pneumoniae, as opposed to most other pathogens, is:
A. Blood agar
B. Mueller-Hinton agar
C. Mueller-Hinton agar with 5% sheep’s blood
D. Chocolate agar or “Chocolated” Mueller-Hinton agar
E. Lowenstein-Jensen agar
20. When treating an eye with a topical antibiotic, the patient should not taper off of the
medication but should maintain the indicated dosage until the very end of the
treatment period, because:
A. To reduce the chances that the pathological organism will develop a resistance
to the medication.
B. To more effectively kill opportunistic organisms not as influenced by the drug.
C. To kill off the normal flora in order to aseptisize the affected area.
D. To allow more time to kill resistant strains of the pathogenic organism.
E. To disrupt the corneal epithelium so as to get more drug into the cornea.
21. The form of trauma called “antecedent trauma” is that which:
A. Removes the corneal or conjunctival epithelium as in an abrasion.
B. Occurs prior to an infection and is necessary for the infection to occur.
C. Occurs as a result of eye surgery.
D. Heals improperly causing a raised or elevated corneal area.
E. Occurs as a result of topical antibiotic drops.
22. An organism that is ubiquitous:
A. Is present only in colonies hidden from direct sunlight.
B. Feeds off of sodium fluorescein in solution.
C. Increases resistance to the antibiotic being used to kill it.
D. Is present all over in nature.
E. Remains viable through formation of a spore or cyst.
23. Pseudomembranes or membranes that form over the palpebral conjunctiva are
different in that:
A. Pseudomembranes can be easily removed from the conjunctival surface but
membranes are more attached, such that portions of the surface are
removed with them.
B. Pseudomembranes are caused by bacteria and membranes by viruses.
C. Pseudomembranes are made of a different material than membranes.
D. Pseudomembranes are toxic and membranes are allergenic.
E. Pseudomembranes respond to anti-bacterial agents and membranes do not.
24. Use of the following topical agent is contraindicated in cases of fungal or suspected
fungal keratitis or corneal ulceration:
A. Ophthalmic tobramycin drops.
B. Natamycin drops.
C. A special mixture of Amphotericin B drops.
D. Ophthalmic corticosteroid drops.
E. Ocular lubricants.
25. Which of the following organisms is a multi-cellular pathogen of the eye?
A. Acanthamoeba sp.
B. Toxocara sp.
C. Microsporidia sp.
D. Chlamydia trachomatis
E. Herpes simplex
26. The proportion of asymptomatic adults having a Gram (-) rod as a normal bacterial
ocular flora is approximately:
A. 0 out of 5
B. 1 out of 5
C. 2 out of 5
D. 3 out of 5
E. 4 out of 5
27. There are several ocular viral pathogens that are “Herpes-like.” Which of the
following is a “Herpes-like” virus?
A. Chlamydia psittaci
B. Adenovirus
C. Varicella virus
D. Coxsackie virus type A24
E. HIV / AIDS virus
28. The causative agents of Acute Hemhorrhagic Conjunctivitis are:
A. Adenovirus types 8 and 19 viruses
B. Varicella and Herpes zoster viruses
C. Verrucae and Papilloma viruses
D. Flu and Common Cold viruses
E. Enterovirus type 70 and Coxsackie type A24 viruses
29. The standardized agar used to perform disc diffusion susceptibility testing for
Moraxella lacunata, as opposed to most other pathogens, is:
A. Mueller-Hinton agar
B. Lowenstein-Jensen agar
C. Sabouraud's agar with or without an antibacterial
D. Mueller-Hinton agar with 5% sheep’s blood
E. Mueller-Hinton agar with 5% sheep’s blood, chocolated
30. The Gram (+) organism most frequently associated with eyelid margin infections is:
A. Pseudomonas aeruginosa
B. Proprionibacterium acnes
C. Haemophilis influenzae
D. Neisseria gonorrhea
E. Staphylococcus aureus
31. The Gram (+) organism second-most frequently associated with eyelid margin
infections is:
A. Pseudomonas aeruginosa
B. Proprionibacterium acnes
C. Haemophilis influenzae
D. Neisseria gonorrhea
E. Staphylococcus aureus
32. The Gram (+) organism causing almost all eyelid hordeola is:
A. Pseudomonas aeruginosa
B. Haemophilis influenzae
C. Moraxella lacunata
D. Staphylococcus aureus
E. Proprionibacterium acnes
33. The "MBC" of an antibiotic is:
A. Maximum concentration of bacteria to have growth visibly inhibited by the
antibiotic.
B. Maximum concentration of bacteria in which 99.9% are killed by the drug.
C. Lowest concentration of antibiotic that kills 99.9% of the bacterial inoculum.
D. The medium (agar) of choice, on which the bacteria are susceptible to the
antibiotic.
E. Lowest concentration of antibiotic that inhibits visible bacterial growth.
34. The "MIC" of an antibiotic is the:
A. Maximum concentration of bacteria to have growth visibly inhibited by the
antibiotic.
B. Maximum concentration of bacteria in which 99.9% are killed by the drug.
C. Lowest concentration of antibiotic that kills 99.9% of the bacterial inoculum.
D. The medium (agar) of choice, on which the bacteria are susceptible to the
antibiotic.
E. Lowest concentration of antibiotic that inhibits visible bacterial growth.
35. The diameters of the inhibitory zones around penicillin and gentamicin sensi-discs are
18 mm and 10 mm, respectively. You may properly conclude one of the following:
A. The bacterium is more susceptible to penicillin than to gentamicin.
B. The bacterium is less susceptible to penicillin than to gentamicin.
C. The bacterium is equally susceptible to penicillin and gentamicin.
D. The bacterium is not susceptible to either penicillin or gentamicin.
E. None of these conclusions are supported by the information available.
36. A weak Beta (β) hemolysis is signified by a(n) ______halo surrounding a colony
on blood agar.
A. white
B. clear/transluscent
C. absence of
D. yellow or orange
E. light green
37. A strong Beta (β) hemolysis is signified by a(n) ______halo surrounding a
colony on blood agar.
A. white
B. clear/transluscent
C. absence of
D. yellow or orange
E. green
38. An Alpha (α) hemolysis is signified by a(n) ______halo surrounding a colony
on blood agar.
A. white
B. clear/transluscent
C. partial
D. yellow or orange
E. green
39. Which of the following tests could be used to differentiate ocular Gram (+)
Streptococci as Streptococcus pyogenes or Streptococcus pneumoniae.
A. "P" disc (optochin)
B. Coagulase reaction or mannitol fermentation
C. Catalase reaction
D. "A" disc (bacitracin)
E. Type of hemolysis
40. A β-hemolytic Streptococcus that is resistant to the "A" disc (bacitracin) is:
A. Pseudomonas aeruginosa
B. Streptococcus pneumoniae
C. Serratia marsescens
D. Streptococcus agalactiae
E. Streptococcus pyogenes
41. Cytology of a conjunctival scrape for an eye having signs and symptoms of ocular
inflammation is mononuclear, showing only many mononuclear cells like lymphocytes
mixed among the epithelial cells. Without consideration of the signs and symptoms, the
most likely diagnosis for this eye is:
A. Bacterial infection
B. Fungal infection
C. Chlamydial infection
D. Viral infection
E. Protozoan infection
42. Cytology of a conjunctival scrape for an eye having signs and symptoms of ocular
inflammation is polymorphic, showing PMNs and mononuclear cells like lymphocytes
mixed among the epithelial cells. Without consideration of the signs and symptoms, the
most likely diagnosis for this eye is:
A. Bacterial infection
B. Fungal infection
C. Chlamydial infection
D. Viral infection
E. Protozoan infection
43. Cytology of a conjunctival scrape for an eye having signs and symptoms of ocular
inflammation is polynuclear, showing only many polymorphonuclear cells. Without
consideration of the signs and symptoms, the most likely diagnosis for this eye is:
A. Bacterial infection
B. Fungal infection
C. Chlamydial infection
D. Viral infection
E. Protozoan infection
44. You cultured from a corneal ulceration of your patient onto blood agar and the
laboratory sent back the results as negative (no growth). Which of the following is
the most true?
A. The ulcer is best referred to as a “sterile ulcer.”
B. The ulcer is best referred to as a “culture-negative” ulcer.
C. The ulcer is the result of a bacterial infection that merely did not grow on agar.
D. The ulcer is the result of a viral infection.
E. The ulcer is the result of a mycobacterial or fungal infection.
45. Which of these organisms is actually not a parasite, but merely an eye pathogen?
A. Entamoeba histolytica
B. Chlamydia trachomatis
C. Acanthamoeba culbertsoni
D. Herpes simplex
E. Onchocerca volvulus
46. Three microorganisms that can thrive in waxy, oily environments and that are involved
in most of the human eyelid infections and meibomian gland dysfunction are:
A. Moraxella lacunata, Staphylococcus aureus, Candida albicans
B. Moraxella lacunata, Haemophilus aegyptius, Mycobacterium fortuitum
C. Haemophilus aegyptius, Streptococcus pneumoniae, Candida albicans
D. Haemophilus influenzae, Streptococcus pneumoniae, Malassezia furfur
E. Propionibacterium acnes, Staphylococcus aureus, Malassezia furfur
47. Intracellular parasites include all of the following except:
A. Viruses
B. Chlamydia
C. Mycobacteria
D. Microsporidia
E. Toxoplasma gondii
48. In response to therapy with Amphotericin B, Candida albicans will most likely:
A. change, in part, from a large colony form into a small colony form which is
more resistant.
B. change from a yeast into a more resistant mold.
C. form spores which will be more resistant.
D. form cysts which will be more resistant.
E. be rendered nonviable but not killed.
49. Characteristics of the organism most associated with a keratoconjunctivitis involving
blue-green purulence include the following except:
A. Can penetrate the intact human corneal epithelium.
B. Can feed off of sodium fluorescein in solution.
C. Can penetrate the cornea 24 to 48 hours after initial infection.
D. The most virulent corneal pathogen.
E. Is involved with a significant number of contact lens-related eye infections.
50. Identify a bacterium or group of bacteria that is a gram (-) coccus:
A. Haemophilus sp.
B. Streptococcus pyogenese
C. Moraxella catarrhalis
D. Proteus mirabilis
E. Serratia marcescens
51. What culture medium could be used to culture from eyes in order to consistently grow
the greatest number of different fungal ocular pathogens ?
A. Chocolate agar
B. Sabouraud's agar
C. Thioglycolate broth
D. Blood agar
E. Trypticase soy agar
52. A fibrinous exudate is generally associated with a bacterium that causes a
mucopurulent conjunctivitis. This organism is:
A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Herpes simplex
D. Corynebacterium diphtheriae
E. Chlamydia trachomatis
53. You cultured from a corneal ulceration of your patient onto blood agar and the
laboratory results were positive (4 colonies of Serratia marcescens). Which of the
following is most true?
A. The ulcer is best referred to as a “sterile ulcer.”
B. The ulcer is the result of a mycobacterial or fungal infection.
C. The ulcer is the result of a viral infection.
D. The ulcer is a “culture-positive” ulcer with Serratia marcescens as the
suspected causative agent.
E. The ulcer is really culture-negative because the colonies were not derived from
bacteria that came from the patient’s cornea.
54. The patient complains of mild red eyes, bilaterally, that became red shortly after a
weekend visit to the YucatanPeninsula. Now 10 days later, a slight mucous
discharge is present and your microbiologist sees inclusions within the cytoplasm of
cells scraped from the conjunctival surface through a light microscope. Your
diagnosis and treatment:
A. Chlamydial infection, treat only with topical antibiotic.
B. Chlamydial infection, treat with systemic and perhaps also topical antibiotics.