Resistance of enteropathogenic strains of Escherichia coli to penicillins and cephalosporins

56 strains of enteropathogenic E. coli, isolated from feces of babies suffering from diarrhea, were examined for their sensitivity to penicillin, dihydrostreptomycin, tetracycline and chloramphenicol. Sixty two per cent of the strains were found to be resistant to these four antibiotics. Their antibiotic resistance could be transferred by conjugation to a sensitive recipient. All the penicillin resistant strains were shown to produce periplasmic β lactamase, the level of which was highest in the strains of the serotype O₅₅B₅. Three strains of different serotypes were used for further investigation. No clear correlation was found between the β lactamase level or the specificity of this enzyme and the resistance of the bacteria to different penicillins. Among the examined penicillins and cephalosporins, only cloxacillin, dicloxacillin, cephaloridine and cephalothin inhibited the growth of these strains. Significant permeability barriers for penicillins but not for cephaloridine and cephalothin were found in the three strains examined. These permeability barriers were markedly reduced in the presence of a subinhibitory concentration of EDTA.