Analytical profile index

API 20NE Detection system after 24 hours incubation.

The analytical profile index or API is a classification of bacteria based on experiments, allowing fast identification. This system is developed for quick identification of clinically relevant bacteria. Because of this, only known bacteria can be identified.

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

The API 20E/NE fast identification system combines some conventional tests and allows the identification of a limited number of Gram-negative Enterobacteriaceae or non-Enterobacteriaceae. The test systems are stored in 20 small reaction tubes, which include the substrates. An identification is only possible with microbiological culture. To guarantee a comparability of different samples, follow the introductions of the manufacturer.

Before starting a test, one must confirm the culture is of an Enterobacteriaceae. To test this, a quick oxidase test for cytochrome c oxidase is performed. Enterobacteriaceae are typically oxidase negative, meaning they either do not use oxygen as an electron acceptor in the electron transport chain, or they use a different cytochrome enzyme for transferring electrons to oxygen. If the culture is determined to be oxidase positive, alternative tests must be carried out to correctly identify the bacterial species.

Further reading

• United States Patent Office, Patent Number 3936356 [1]
• API System: a Multitube Micromethod for Identification of Enterobacteriaceae, P. B. Smith, K. M. Tomfohrde, D. L. Rhoden, and A. BalowsCenter for Disease Control, Atlanta, Georgia 30333 [2]