SUMMARY A high prevalence of multiple antibiotic resistance was observed in populations of Escherichia coli isolated from 2 large groups of calves in a commercial veal-rearing unit. Almost all of the cultures isolated were resistant to tetracyclines, streptomycin, neomycin, and kanamycin after the calves had been given rations containing neomycin for 1 week. The number of cultures with resistance to ampicillin also increased during antibiotic feeding, despite the fact that it was not utilized in the ration or for therapy. Association between the therapeutic use of chloramphenicol and isolation of E. coli with resistance to this antibiotic was observed. A total of 65% of the multiply resistant cultures of E. coli examined was capable of transferring resistance determinants to a laboratory strain of E. coli K-12 or to Salmonella saintpaul isolated from the calves.
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Loken et al. (1971) studied this question.