Cephalosporinase and penicillinase activities of a β-lactamase from Pseudomonas pyocyanea

Abstract

Pseudomonas pyocyanea N.C.T.C. 8203 produces a [beta]-lactamase that is inducible by high concentrations of benzylpenicillin or cephalo-sporin-C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. No evidence was obtained that the crude enzyme preparation consisted of more than one [beta]-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. The maximum rate of hydrolysis of cephalosporin-C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolyzable substrates. Cephalosporin-C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin-C yielded 1 equiv./mole. Evidence was obtained that the opening of the [beta]-lactam ring of cephalosporin-C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolyzable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a [beta]-lactamase contributed to the factors responsible for the very high resistance of P. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.