Differentiation of strains of Escherichia coli: multiple typing approach.

Results from biotyping, resistotyping, hemagglutinin typing, and antibiotic sensitivity testing allowed discrimination of 184 cultures of Escherichia coli and indicated that from each of 20 patients, multiple specimens yielded isolates of a single strain despite the diversity of sites sampled; from each of another 13 patients, strains of different types were isolated. Whereas only 52% of cultures were typed with 24 commerical O antisera, all were characterized by biotyping (27 types) and resistotyping (39 types). Because they identified too few types, hemagglutinin testing (14 types) and antibiogram testing (9 types) were of limited discriminatory value when used alone but aided strain identification when used in conjunction with biotyping and resistotyping. Identification of strains as the same or different is most likely to be achieved by the combined use of several of these systems, each of which may be used in laboratories unable to perform complete serological analysis of strains of E. coli, and we judge that biotyping and resistotyping would provide the most useful information.