Comparative Activity of Bacterial -Lactamases on Penicillins and Cephalosporins

Abstract

Beta-Iactamases derived from Staphylococcus, Enterobacteriaceae, and two types of Pseudomonas aeruginosa were partially purified and characterized by starch-gel electrophoresis. A comparison was made of their capacity to hydrolyze benzyl penicillin and five different cephalosporins that were semimatched in pairs according to the chemical substituents. An iodometric method of measurement was used that permitted estimations of avidity and quantitation of the relative velocity of the reactions. Under conditions of the test, β-lactamases from Staphylococcus and from one strain of P. aeruginosa were specific penicillinases, and those from Escherichia coli and from another strain of P. aeruginosa were preferential penicillinases but also cephalosporinases. Beta-lactamases from Klebsiella pneumoniae, Enterobacter cloacae, and penicillin-induced strains of P. aeruginosa all were active cephalosporinases. Cefazolin was the most labile of the cephalosporins, and cephanone the most resistant. Marked differences were related to the molecular structures of the drugs, especially in the nature of the substituted amide at position 7 of the cephalosporin nucleus; less effect was related to substitutions in the 3-methyl group.