Analytical profile index

The analytical profile index, or API, is a classification of bacteria based on biochemical tests, allowing fast identification. The system is developed for the quick identification of clinically relevant bacteria, and because of this can only be used to identify known species.

It was invented in the 1970s in the United States by Pierre Janin of Analytab Products Inc. The API test system is currently manufactured by bioMérieux. The API range introduced a standardized and miniaturized version of existing techniques, which up until then were complicated to perform and difficult to read.

One of the API systems, API-20E, is specific for differentiating between members of the Gram-negative bacteria family Enterobacteriaceae. Another API system, API-Staph, is specific for Gram-positive bacteria, including Staphylococcus species, Micrococcus species, and related organisms.

API test strips consist of wells containing dehydrated substrates to detect enzymatic activity, usually related to the fermentation of carbohydrate or catabolism of proteins or amino acids by the inoculated organisms. A bacterial suspension is used to rehydrate each of the wells and the strips are incubated. During incubation, metabolism produces color changes that are either spontaneous or revealed by the addition of reagents. For example, when carbohydrates are fermented, the pH within the well decreases and that change is indicated by a change in the color of the pH indicator. All positive and negative test results are compiled to obtain a profile number, which is then compared with profile numbers in a commercial codebook (or online) to determine the identification of the bacterial species.