Biotyping of Escherichia coli in microwell plates.

A simple, inexpensive scheme of eight tests for biotyping strains of Escherichia coli in microwell plates is described. The tests comprise primary tests for the fermentation of raffinose, sorbose, ornithine, dulcitol and 2-deoxy-D-ribose, and secondary tests for rhamnose fermentation, lysine decarboxylation and motility. Among a collection of 75 clinical isolates of Esch. coli from 12 patients, 18 full biotypes designated according to their positive and negative reactions in the eight tests were distinguished. These biotypes gave an indication of the natural history of patients' infections. Because it provides excellent and reliable type discrimination, biotyping can be used in a combination with other typing techniques to resolve local epidemiological problems involving Esch. coli.