Identification of gram-negative aerobic fermentors in a clinical bacteriological laboratory

A basic set of six biochemical tests (indol, urease, hydrogensulphide production, acetoin, ornithine decarboxylase andΒ-galactosidase) were selected from an original set of fourteen tests and found to give more than 97% accurate reactions within 18 h of incubation for the identification of bacteria belonging toEnterobacteriaceae. This set permits identification on the genus and/or species level forEscherichia, Shigella, Salmonella, Edwardsiella, Citrobacter andProteus. For theKlebsiella-Enterobacter-Serratia group, where a species diagonsis was considered desirable, eight additional tests (esculin, raffinose, sorbitol, malonate, citrate, lysine decarboxylase, deoxyribonuclease and motility) permitting identification within 18 to 72 h were added. The use of this two-step test set for the identification of almost 6000 strains isolated from clinical specimens during an eight month period is reported.