Drug-resistance and distribution of conjugative R plasmids in Escherichia coli strains isolated from healthy adult animals and humans.

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Abstract
A total of 13,455 E. coli strains were isolated from 103 hens, 109 pigs, 122 cows and 117 humans during 1978-1979 in Gunma prefecture [Japan] and tested for drug resistance and conjugative R plasmids. About 30 E. coli strains were collected from each individual. Criteria for drug resistance were: tetracycline, 12.5 .mu.g/ml; chloramphenicol, 12.5 mg/ml; streptomycin, 12.5 .mu.g/ml; sulfonamides, 200 .mu.g/ml; kanamycin, 25.0 .mu.g/ml and aminobenzylpenicillin, 25.0 .mu.g/ml. The ratios of individuals that excreted drug-resistant strains and isolation frequency of drug-resistant strains among total isolates in each animal species were: hens, 100%, 95%; pigs, 100%, 95%; cows, 66%, 54%; and humans, 65%, 39%. The ratios of R plasmid-bearing individuals and isolation frequency of R plasmids among strains tested were: hens, 67%, 42%; pigs, 72%, 35%; cows, 34%, 20%; and humans, 19%, 19%. Doubly to quadruply resistant strains were isolated most frequently from hens and pigs; from cows and humans, single-resistant strains were isolated most frequently among resistant strains. The highly frequent appearance of drug-resistant strains and R plasmids among hens and pigs reflects heavy application of drugs.