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A potent fl-lactamase (EC 3.5.2.6) produced by a strain of Klebsiella aerogenes (K. pneumoniae), 1082E, isolated from a hospital patient, has been examined. Its properties were different from those of most gram-negative f-lactamases previously reported. The enzyme has been partly purified, and its activity against a range of substrates has been compared with that of the enzyme from Enterobacter cloacae (Aerobacter cloacae) P99. The K. aerogenes enzyme, although predominantly a penicillinase, had a wide range of specificity. In addition to hydrolyzing the cephalosporins, it attacked the normally fl-lactamaseresistant compounds methicillin and cloxacillin as well as cephalosporin analogues with the same acyl substituents. The results obtained with the E. cloacae enzyme confirmed its cephalosporinase activity and showed that, unlike the enzyme from K. aerogenes, it was relatively inactive against the penicillins. The fl-lactamases produced by gram-negative bacteria differ considerably in their substrate specificities. Although most of the enzymes hydrolyze penicillin G, cephalothin, and cephaloridine, comparatively few hydrolyze methicillin or cloxacillin.

A potent β-lactamase (EC 3.5.2.6) produced by a strain of Klebsiella aerogenes ( K. pneumoniae ), 1082E, isolated from a hospital patient, has been examined. Its properties were different from those of most gram-negative β-lactamases previously reported. The enzyme has been partly purified, and its activity against a range of substrates has been compared with that of the enzyme from Enterobacter cloacae ( Aerobacter cloacae ) P99. The K. aerogenes enzyme, although predominantly a penicillinase, had a wide range of specificity. In addition to hydrolyzing the cephalosporins, it attacked the normally β-lactamaseresistant compounds methicillin and cloxacillin as well as cephalosporin analogues with the same acyl substituents. The results obtained with the E. cloacae enzyme confirmed its cephalosporinase activity and showed that, unlike the enzyme from K. aerogenes , it was relatively inactive against the penicillins.

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