The API-20E test kit for
the identification of enteric bacteria (bioMerieux,
Inc., Hazelwood, MO) provides an easy way to
inoculate and read tests relevant to members of the Family
Enterobacteriaceae and associated organisms. A plastic strip holding
twenty mini-test tubes is inoculated with a saline suspension of a pure culture
(as per manufacturer's directions). This process also rehydrates the dessicated
medium in each tube. A few tubes are completely filled (CIT, VP and GEL as seen
in the photos below), and some tubes are overlaid with mineral oil such that
anaerobic reactions can be carried out (ADH, LDC, ODC, H2S,
URE).
After incubation in a
humidity chamber for 18-24 hours at 37°C, the color reactions are read (some
with the aid of added reagents), and the reactions (plus the oxidase reaction
done separately) are converted to a seven-digit code. The code is fed into the
manufacturer's database via touch-tone telephone, and the computer voice gives
back the identification, usually as genus and species. The reliability of this
system is very high, and one finds systems like these in heavy use in
many food and clinical lab