The incidence of infective drug resistance in strains ofEscherichia coliisolated from diseased human beings and domestic animals

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Abstract
A high incidence of drug resistance, mostly of the infective type, was found amongst strains of Escherichia coli isolated from human beings suffering from neonatal diarrhoea, calves and lambs suffering from neonatal diarrhoea or bacteraemia, pigs suffering from neonatal or post-weaning diarrhoea or bowel oedema and from fowls suffering from ‘coli-septicaemia’. The strains from the human beings, pigs and fowls, and those from calves and lambs suffering from bacteraemia, belonged to serotypes generally accepted as being pathogenic for these species.Complex drug-resistance patterns were a common feature, particularly amongst the human and calf strains, some being resistant to six drugs. Only two drugs, polymyixin and nalidixic acid, were active on all the strains.The incidence of drug resistance amongst pig strains was twice as great in those isolated in 1965 as in those isolated in 1960–62; neomycin and furazolidone resistance was found amongst the 1965 strains but not amongst the 1960–62 strains.Infective resistance was easily demonstrated; tetracycline resistance was transferred from one tetracycline-resistant strain of E. coli to 37 of 38 tetracycline-sensitive strains at the first attempt.Most ampicillin, streptomycin, tetracycline, chloramphenicol, neomycin and sulphonamide resistance was of the infective type; the furazolidone resistance in all of eight strains studied was not shown to be infective.In the experiments to demonstrate the presence of infective resistance the level of drug resistance was usually found to be the same in donor and recipient strains.