The use of  -Lactamases in the Clinical Laboratory

SUMMARY Eleven β-lactamases were tested for their ability to destroy the currently available β-lactam antibiotics. The biochemical activities of the enzymes against cephaloridine and benzylpenicillin were compared by iodometric assay. Their biological activity was tested by mixing various amounts of enzymes and of 13 different β-lactam antibiotic preparations and assaying the residual antibiotic by an agar-diffusion method, with Sarcina lutea as the test organism. All the enzymes destroyed 500 µg per ml of benzylpenicillin and the more potent ones also destroyed “penicillinase-resistant” penicillins and cephalosporins. Crude enzyme extracts from a strain of Enterobacter aerogenes and of Klebsiella aerogenes compared favourably with the bacillus enzymes in their action on cephalosporins. Suitable β-lactamases can therefore be used to destroy all the available β-lactam antibiotics in specimens from patients, either in blood cultures or to allow the assay of other antibiotics in patients being treated concurrently with both.