Question: Why
was the oxidase test performed on the infectious agent from the
patient?Why was the antibioti…
was the oxidase test performed on the infectious agent from the
patient?Why was the antibiotic sensitivity testing ordered?
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CASE FILE A 52-year-old woman in Georgia visited her physician com- plaining of pain, redness, light sensitivity, and swelling in her right eye. The doctor observed a corneal abrasion, which the patient reported was caused by a mascara applicator He applied gentamicin ointment and patched the eye. Two days later, no improvement was observed and the abrasion had abscessed. Corneal scrapings from the abscess were Gram stained as described in exercise 11, revealing the presence of gram- negative bacilli. The patient's mascara and corneal scrapings w cultured. A number of gram-negative bacteria can cause corneal infec- tions, so additional biochemical testing of the culture was required to identify the causative bacteria. Test results, including the oxidase test, revealed the presence of Pseudomonas aeruginosa. Since Pseudomonas frequently exhibits antibiotic resistance, antibiotic-sensitivity testing was immediately ordered. Pseudomonas has also shown the ability to grow on a surprisingly wide range of materials, including iodophor antiseptics, exfoliative sponges, and, as seen in this case, mascara.
