catalasepositive

Catalase-positive refers to microorganisms that produce the enzyme catalase, which converts hydrogen peroxide into water and oxygen. This enzymatic activity helps cells detoxify reactive oxygen species generated during aerobic metabolism or encountered within host environments.

In microbiology, a catalase test is used to distinguish catalase-positive from catalase-negative organisms. A small amount of bacterial growth is exposed to hydrogen peroxide (commonly 3%). Immediate bubbling indicates a positive result, showing active breakdown of hydrogen peroxide. Absence of bubbles indicates a negative result. Some strains may appear weakly positive, and proper technique, fresh cultures, and appropriate controls are important to avoid misleading results.

Classically, catalase positivity is used to differentiate Staphylococcus species (catalase-positive) from Streptococcus and Enterococcus species (catalase-negative). Many other aerobic or facultatively aerobic bacteria, including Escherichia coli and Pseudomonas aeruginosa, are catalase-positive as well. The trait is not exclusive to a single group and can vary among organisms. In addition, catalase activity can be found in certain fungi, such as some Candida species, though testing is less routine in fungal identification.

Clinical relevance and limitations: the catalase test is a rapid, presumptive aid in initial bacterial identification and in guiding subsequent biochemical testing. It should be interpreted in the context of Gram stain results and other phenotypic tests, as catalase positivity alone does not confirm a specific species.