The analytical profile index or API is a

classification Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. Classification is the grouping of related facts into classes. It may also refer to: Business, organizat ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

based on biochemical tests, allowing fast

identification Identification or identify may refer to: *Identity document, any document used to verify a person's identity Arts, entertainment and media * ''Identify'' (album) by Got7, 2014 * "Identify" (song), by Natalie Imbruglia, 1999 * 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 bioMérieux SA is a French multinational biotechnology company founded and headquartered in Marcy-l'Étoile, France, close to Lyon. bioMérieux is present in 44 countries and serves more than 160 countries through a large network of distributors ...

. The API range introduced a standardized, miniaturized version of existing techniques, which up until then were complicated to perform and difficult to read. One of the API systems is specific for differentiating between members of the Gram negative bacterial Family Enterobacteriaceae and is called API-20E. The other API system is specific for Gram positive bacteria, including Staphylococcus species, Micrococcus, species, and related organisms, and is called API-Staph. API test strips consists of wells containing dehydrated substrates to detect enzymatic activity, usually related to 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.

API 20E/NE

The API 20E/NE fast identification system combines some conventional tests and allows the identification of a limited number of

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

Enterobacteriaceae Enterobacteriaceae is a large family (biology), family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject ...

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 A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagn ...

. Before starting a test, one must confirm the culture is of an Enterobacteriaceae. To test this, a quick oxidase test for

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory electr ...

is performed. Enterobacteriaceae are typically oxidase negative, meaning they either do not use oxygen as an electron acceptor in the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

, 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.

API 20E/NE

References

Further reading