Microbiology

Microbiology is 2% of the COA exam. It covers the organisms that infect eyes and the habits that keep a clinic from passing them from one patient to the next.

The surface is not sterile — healthy lids and conjunctiva carry resident bacteria, mostly staphylococci, without harm. Tears defend the surface by flushing it and with natural antibacterial proteins such as lysozyme. Infection follows when the barrier breaks (an abrasion, a contact lens, surgery, an injury), when the usual bacteria overgrow (blepharitis, styes), or when an aggressive organism arrives.

Common ocular pathogens — adenovirus (epidemic keratoconjunctivitis, EKC, famously contagious in eye clinics), staph and strep species, Pseudomonas (contact lens keratitis), and Acanthamoeba (tap-water contact lens exposure).

Why the history matters — the story often names the organism before any culture does. The assistant who asks about contact lens habits, water exposure, plant injuries, sick contacts, and recent steroid drops gives the physician the most useful clue.

The contact lens red flag — a painful red eye in a lens wearer is a same-day visit: lenses out, and bring the lenses and the case.

Hand hygiene — before and after every patient contact; the single most effective way to keep infection from spreading in the clinic. Clean hands again after removing gloves; gloves do not replace hand hygiene.

Rub or wash — alcohol-based hand rub suits most routine contact, but it works less well against adenovirus and bacterial spores. Wash with soap and running water when hands are visibly soiled and after caring for a patient with suspected EKC.

Standard precautions — treat all blood and certain body fluids as potentially infectious. Tears and eye discharge count.

Choose protection by task — gloves for contact with tears, discharge, mucous membranes, or broken skin. Add a mask, eye protection, and a gown when splash or spray is possible.

Sharps — straight into an approved rigid container, never recapped by hand.

What an item touches decides how it is processed — items that enter sterile tissue or the bloodstream are sterilized, items that touch mucous membranes or broken skin, including the surface of the eye, get high-level disinfection, and items that touch only intact skin get low-level disinfection.

Instrument disinfection — anything touching the tear film (tonometer tips, gonio lenses, trial contact lenses) is disinfected between patients per CDC and manufacturer protocol; dry wiping is not disinfection. A reusable tonometer tip gets a timed soak in an approved disinfectant (diluted bleach is one some protocols use), then a thorough rinse and dry. Autoclaving damages the tip. Disposable tips avoid the question.

Rinse what touches the eye — disinfectant left on a lens or tip can burn a cornea that has just been numbed and cannot feel it.

Contact time — every disinfectant label lists a contact time. The surface must stay visibly wet for that whole time; a quick swipe that dries in seconds has not disinfected the chin rest.

Drops and dyes — the dropper tip never touches the lids, lashes, or eye. Date bottles when opened and discard per policy. Fluorescein solution can grow Pseudomonas, one reason single-use sterile strips are common.

Adenovirus survives on surfaces for weeks and spreads through contaminated instruments, shared drops, and hands. EKC outbreaks start with a contaminated instrument or an unwashed hand.

Spot it early — a watery red eye, a sick contact, and a tender node in front of the ear make the story. Flag it as early as possible.

Contain it — room the patient promptly and apart from others if the office protocol allows. Use disposable or dedicated equipment where possible, and ask the physician before any contact test, such as applanation.

Clean up — wash hands with soap and water afterward, and disinfect every surface the patient touched with a product labeled as effective against adenovirus.

Teach — reinforce the physician's instructions: frequent handwashing, no shared towels or pillowcases, and staying home for as long as the physician advises.

Specimen collection — conjunctival and corneal cultures are taken before antibiotics when the physician orders them; label at the chair, transport per lab protocol. Even a day of antibiotic drops can leave a culture with nothing to grow.

Set up first — have the media, slides, and labels laid out before the physician starts, because a corneal scraping holds only a few cells and must go onto the media at once.

Label at the moment of collection — patient, date, eye, and site on every plate and slide, never later in the day.

Tell the lab what is suspected — fungi and Acanthamoeba need special media, and fungal plates must be held longer, so the suspicion has to travel with the specimen.

Gram stain — sorts bacteria into gram-positive and gram-negative, a quick first look while cultures grow.

Be ready to name the most effective infection-control measure, define standard precautions, choose protection for a task, match adenovirus, Pseudomonas, Acanthamoeba, herpes simplex, fungi, and staphylococci to their classic stories, disinfect a tonometer tip, explain contact time, and handle a culture from collection to the lab.