Ichinomiya City Museum

Antimicrobial susceptibility was examined using 89 enterohemorrhagic Escherichia coli O157 isolates obtained from diarrhea patients in Aichi Prefecture, Japan between June 1996 and June 1997. Among the 89 isolates, 15 (16.9%) were found to be resistant to 6 of 9 antibiotics examined. These 6 antibiotics were ampicillin (ABPC), cefaloridine (CER), chloramphenicol (CP), kanamycin (KM), streptomycin (SM), and tetracycline (TC). Among the 15 drug-resistant isolates, 7 were resistant to 4 drugs (ABPC, CER, SM, TC), 3 were resistant to 3 (ABPC and 2 of CER, SM, TC), 2 were resistant to 2 (SM, TC), one each to KM or SM. Another isolate showed resistance to 5 drugs (ABPC, CP, KM, SM, TC). Selected 13 drug-sensitive and selected 12 multi-drug resistant isolates were tested for the presence of plasmids. All of the drug-sensitive isolates had 54 MDa plasmid and the majority (8/13) had 2.0 MDa plasmids, whereas; all of the drug-resistant isolates except one (1/12) had 54 MDa plasmid and the majority had 8.0 MDa (9/12) and 4.2 MDa (11/12) plasmids. The first transformation test revealed that plasmids of 8.0 MDa (3/4) and 46 MDa (1/4) were transferred to a donor cell with ABPC resistance. 54 MDa plasmid was transferred to a donor cell with both of ABPC and TC resistance. In the second transformation test, only the 8.0 MDa plasmid was confirmed to be transferred to a donor cell with ABPC resistance. Accordingly, it was indicated that the ABPC resistant gene was carried on 8.0 MDa plasmid, and it was suggested that resistant genes for ABPC and TC, and ABPC were carried on 54 MDa, and on 46 MDa plasmids, respectively.