A MINIATURIZED BIOTYPING SYSTEM FOR STRAIN DISCRIMINATION IN ESCHERICHIA-COLI

A two-tier miniaturized scheme of eight tests was devised for biotypin g strains of Escherichia coli in microwell plates. Primary biotypes we re defined by positive and negative reactions in tests for fermentatio n of raffinose, sorbose, dulcitol and 2-deoxy-D-ribose and for decarbo xylation of ornithine when read after specified periods of incubation; subtypes were identified within primary biotypes according to results in secondary tests for rhamnose fermentation, lysine decarboxylation and motility. The method gave reproducible results on different occasi ons of testing. Among 100 E. coli strains from various sources, 26 of the 32 possible primary biotypes and 56 full biotypes, as defined by r esults in both primary and secondary tests, were identified, thus demo nstrating a high index of strain discrimination (D = 0.98). The scheme is recommended as a simple, reliable, inexpensive and efficient metho d of differentiating strains of E. coli.