A total of 11,777 Escherichia coli strains were isolated from 90 chickens, 103 piglets, 96 calves, and 104 children in 1979 in Gunma Prefecture and tested for drug resistance and the presence of conjugative R plasmids, The percentages of individuals that excreted drug-resistant strains were: chickens, 100%; piglets, 99%; calves, 100%; and children, 64%. The frequency of isolation of drug-resistant strains among the total isolates was: chickens, 98%; piglets, 93%; calves, 94%; and children, 41 %. Frequency of isolation of R plasmids among the strains tested was: chickens, 48%; piglets, 33%; calves, 38%; and children, 10%.Resistance patterns of the strains isolated most frequently among the four groups were tetracycline (TC), sulfonamides (SA) in single resistance, TC.SA in double resistance, TC.streptomycin (SM) .SA in triple resistance and TC:SM.SA. kanamycin (KM) in quadruple resistance.R plasmids were isolated frequently from animals (over 33%) but infrequently from children (about 10%).The high frequency of isolation of drug-resistant strains and R plasmids from animals was caused by the heavy use of chemicals in the period of growth of younger animals.In the livestock industry in Japan, animals and fowls are fed and reared in small spaces. These crowded rearing conditions are dangerous, because animals are easily infected with bacteria from others. Especially at the younger ages, infections are not infrequent and many kinds of drugs have been used for prevention of infection as well as for therapy of infectious diseases. This situation may cause the appearance and spread of drug-resistant strains, as has been suggested in many reports (1,4,14,16,19,22,23,25).In a previous paper we presented a detailed survey of resistant strains among livestock and adult humans. Examining as many as 30 strains from each individual animal, we hoped to isolate resistant strains that composed a smaller fraction of the total Escherichia coli cells. The calculated incidence of individuals excreting E. coli cells resistant to a drug would be less than that in the case when the selection is made by drug plates. Nevertheless, the value obtained was moder-1031
