Molecular epidemiological study on tetracycline resistance R plasmids in enterohaemorrhagic Escherichia coli O157 : H7

Restriction patterns obtained with EcoRI and Southern hybridization were us ed for the differentiation of tetracycline-resistant (Tet(r)) R plasmids in enterobaemorrhagic Escherichia coil (EHEC) O157:H7 isolates from a mass ou tbreak at a kindergarten in Obihiro-City, Hokkaido, Japan, 1996. Two kinds of Tet(r) R plasmids of 50 and 95 kb were detected. The 50-kb plasmids were identical to each other, while the 93-kb plasmids were of three types that were very similar to each other. The tet genes of both 50- and 95-kb R pla smids were 100 % identical to the tet gene of pSC101 and all plasmids hybri dized to a probe for tet. Because food-origin O157 strains were sensitive t o tetracycline, we concluded that such Tet(r) R-plasmids might transfer to drug-sensitive O157 strains in the infected individuals.