An inducible beta-lactamase in a strain of Escherichia coli

The production of beta-lactamase (penicillin/cephalosporin beta-lactam amidohydrolase, E.C.3.5.2.6) was found to be inducible in a clinically isolated strain of Escherichia coli. This is the first report of an inducible beta-lactamase in E. coli. The optimal concentration of inducer was 400 mug/ml of ml of benzylpenicillin, or 800 mug/ml of 6-aminopenicillanic acid. About fiftyfold induction was achieved. Maximum induction took ninety minutes from the time of adding the inducer. Induction was abolished by the presence of chloramphenicol(10 mug/ml). The enzyme has a molecular wieght of 23,000, and is inhibited by rho-chloromercuribenzoate and by iodine. It is active against a wide range of substrates, including cephaloridine and cloxacillin.