The oxidase test is used to identify bacteria of which genus, indicated by a positive reaction?

The oxidase test is used to identify bacteria of which genus, indicated by a positive reaction?

• A. Neisseria
• B. Streptococcus
• C. Bacillus
• D. Enterococcus

Answer: (A)

The oxidase test looks for the enzyme cytochrome c oxidase in the bacterial electron transport chain. If the organism has this enzyme, the reagent is oxidized and produces a rapid color change to dark purple within seconds. This distinguishes oxidase-positive organisms from oxidase-negative ones. Neisseria is known to be oxidase positive, which is why a positive oxidase test points to this genus. The other genera listed—Streptococcus, Bacillus, and Enterococcus—typically do not produce cytochrome c oxidase and thus yield a negative result. So a positive reaction best identifies Neisseria.

The oxidase test looks for the enzyme cytochrome c oxidase in the bacterial electron transport chain. If the organism has this enzyme, the reagent is oxidized and produces a rapid color change to dark purple within seconds. This distinguishes oxidase-positive organisms from oxidase-negative ones. Neisseria is known to be oxidase positive, which is why a positive oxidase test points to this genus. The other genera listed—Streptococcus, Bacillus, and Enterococcus—typically do not produce cytochrome c oxidase and thus yield a negative result. So a positive reaction best identifies Neisseria.