Molecular Heterogeneity of Heat-Stable Toxin-Producing and Non-Producing Escherichia coli O25 Strains Isolated in Japan

Escherichia coli O25 strains that produce heat‐stable toxin (ST) have been recently isolated in Japan, and epidemiological study of this type of enterotoxigenic E. coli is required. In this study the heterogeneity of 16 ST‐producing and non‐producing strains of E. coli O25 was investigated. All eight ST‐producing strains were shown to have STIb gene, and seven of them had similar profiles of plasmids, ladder‐banding of LPS in SDS‐polyacrylamide gel electrophoresis, and chromosomal DNA digestions in pulsed‐field gel electrophoresis (PFGE). In contrast, ST‐non‐producing strains were more heterogeneous in all parameters examined. PFGE of the digested chromosomal DNA with several restriction enzymes was proved to be an effective procedure to compare the closely related strains of E. coli O25.