Incidences of antibiotic resistant fecal Escherichia coli strains isolated from healthy human in tokyo area in 1978 and their conjugative R plasmids.

We surveyed antibiotic resistances of fecal Escherichia coli strains from healthy human in Tokyo in 1978 and their conjugative R plasmids. Approxi-mately 50% of healthy human had streptomycin/tetracycline resistant E. coli strains in their intestines. In addition, 34%, 28% and 17% of them had ampicillin, kanamycin, and chloramphenicol resistant strains, respectively. Coincidences of various resistance markers of these isolated strains were higher in the closer markers in the linear order of Km-Sm-Tc-Ap-Cm. Incidences of the single drug resistant conjugative R plasmids in the strains selected by tetracycline, streptomycin, kanamycin and ampicillin were found to be high in these years, but the multiple drug resistant conjugative R plasmids were found to be still predominant in the strains selected by chloramphenicol even though the incidences of these strains had been decreasing. These results might be caused by the present selective chemotherapeutic environments.