Drug Resistance of Enteric Bacteria

Five R factors capable of conferring resistance to ampicillin, together with resistance to 4 other drugs, tetracycline (TC), chloramphenicol (CM), streptomycin (SM) and sulfanilamide (SA), were found in Escherichia coli strains isolated from clinical sources. Ampicillin resistance was due to synthesis of penicillinase in the host bacterium which harbored the R factor. The penicillinases produced by three R factors were similar each other in their substrate specificity and were also similar to the enzyme reported by previous workers. The penicillinases produced by 2 other R factors were found to be greatly difierent from penicilhnases reported thus far. The latter were shown to hydrolyse ampicillin and cloxacillin efficiently, but penicillin‐G and 6‐aminopenicillanic acid to a lesser extent.