COT Microbiology 6

Question 1

Trachoma, the leading infectious cause of preventable blindness worldwide, is caused by Chlamydia trachomatis. Which serotypes (serovars) are responsible for ocular trachoma?

Accepted Answer

Serotypes A, B, and C

Answer

Chlamydia trachomatis serotypes A, B, and C are responsible for endemic trachoma, causing repeated conjunctival inflammation that leads to scarring, trichiasis, and corneal opacification. Serotypes D–K cause inclusion conjunctivitis and genital infections, while serotypes L1–L3 cause lymphogranuloma venereum (LGV), a systemic sexually transmitted infection.

Question 2

A contact lens wearer presents with a rapidly progressive corneal ulcer and severe pain. Corneal scrapings reveal large, double-walled cysts on Giemsa stain. Which organism is the most likely causative agent?

Accepted Answer

Acanthamoeba species

Answer

Acanthamoeba species are free-living protozoa that form characteristic double-walled cysts visible on Giemsa or calcofluor white staining. They cause a devastating keratitis almost exclusively in contact lens wearers, often associated with tap water or homemade saline exposure. The cyst wall distinguishes them from bacterial or fungal etiologies.

Question 3

Which of the following best describes the mechanism by which fluoroquinolone antibiotics (e.g., ciprofloxacin) kill bacteria?

Accepted Answer

Inhibiting DNA gyrase and topoisomerase IV, preventing DNA replication

Answer

Fluoroquinolones inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for DNA supercoiling and replication. This halts DNA replication and transcription, resulting in bacterial cell death. This mechanism is distinct from beta-lactams (cell wall), aminoglycosides (30S ribosome), or polymyxins (membrane disruption).

Question 4

A patient develops acute follicular conjunctivitis with preauricular lymphadenopathy one week after swimming in a public pool. Which pathogen is the most likely cause?

Accepted Answer

Adenovirus

Answer

Adenovirus is the classic cause of epidemic keratoconjunctivitis (EKC) and pharyngoconjunctival fever, frequently transmitted in swimming pools ('swimming pool conjunctivitis'). It produces follicular conjunctivitis with a prominent preauricular lymph node — a key clinical sign. Chlamydia causes chronic follicular conjunctivitis, while gonococcal disease causes hyperacute purulent discharge.

Question 5

In the context of ophthalmic instrument disinfection, which method achieves the highest level of microbial kill, including bacterial endospores?

Accepted Answer

Sterilization via autoclave (steam under pressure)

Answer

Autoclaving (steam sterilization at 121°C, 15 psi for 15–30 minutes) is the gold standard for sterilization — it destroys all microbial life including highly resistant bacterial endospores (e.g., Bacillus and Clostridium). Glutaraldehyde achieves sterilization only after extended contact (10 hours), not 20 minutes. Alcohols and quaternary ammonium compounds do not reliably kill spores.

COT - Certified Ophthalmic Technician Practice Test

COT - Certified Ophthalmic Technician Practice Test

COT Microbiology 6