Pseudomonas aeruginosa is best described as which of the following?

• A. Oxidase positive; grape-like odor; salmon-colored sputum
• B. Oxidase negative; grape-like odor
• C. Gram-positive cocci
• D. Causes purulent conjunctivitis in healthy adults

Answer: (A)

Pseudomonas aeruginosa is defined by being an oxidase-positive, Gram-negative rod that often causes opportunistic infections in hospitalized patients and those with underlying lung disease or burns. The oxidase-positive result reflects the presence of cytochrome c oxidase, a key test that helps distinguish Pseudomonas from many Gram-negative rods in the Enterobacteriaceae, which are oxidase negative. The grape-like odor is a classic, memorable clue to this organism in the right clinical context. In addition, pigment production (pyocyanin and pyoverdin) can color secretions such as sputum, which helps reinforce identification, though the exact color can vary and is not the sole diagnostic feature. The other statements don’t fit because the organism is not a Gram-positive cocci, it is not oxidase negative, and while it can cause eye infections in some settings, describing it as causing purulent conjunctivitis in healthy adults is not a reliable general description of this pathogen.