oxidasenegative

Oxidasenegative, commonly written as oxidase-negative or oxidase negative, is a term used in microbiology to describe organisms that do not produce the enzyme cytochrome c oxidase or do not transfer electrons to oxygen via that enzyme. The distinction is part of a set of biochemical tests used to identify bacteria, particularly among Gram-negative rods.

The oxidase test is the principal method for determining oxidase status. A culture is tested by applying a reagent, such as tetramethyl-p-phenylenediamine (TMPD), to a sample of the organism. If cytochrome c oxidase is present, the reagent is oxidized and turns purple within seconds to a minute. If the organism is oxidase-negative, there is no color change. The test is rapid, inexpensive, and commonly used in clinical and environmental microbiology.

Oxidasenegative organisms include many members of the Enterobacterales and other related genera, such as Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Proteus spp., Salmonella spp., and Shigella spp., as well as Acinetobacter spp. In contrast, oxidase-positive organisms include genera such as Pseudomonas and Neisseria. The test helps laboratories rapidly distinguish oxidase-negative enteric bacteria from oxidase-positive non-fermenters, guiding initial identification and management decisions.

Limitations of the oxidase test include the potential for false results due to outdated reagents, improper timing, or residual reducing agents in media. Some organisms may yield weak or delayed reactions, and environmental factors such as temperature can influence outcomes. Consequently, oxidase status is interpreted alongside other biochemical tests.