Induction of B - Lactamase in Gram - negative bacteria

Abstract

With the aim of studying the 13-lactamase induction in some gram­

negative bacteria, different isolates were collected and screened for 13- lactamase production by using the chromogenic cephalosporin, nitrocefin as substrate. Out of these isolates, Citrobacter jreundii, Escherichia coli 1048, Proteus mirabilis, Proteus vulgaris 1753, Pseudomonas aeruginosa and Serratia marcescens 921/79 showed ability for 13-lactamase production. These 13-lactamase-producing bacteria were plasmid-free and produced chromosomally encoded enzyme.

The induction of 13-lactamase in clinical isolates of C. jreundii, E. coli

1048, P. mirabilis, P. vulgaris 1753, P. aeruginosa and S. marcescens • 921/79 by structurally different 13-lactam antibiotics was studied. High 13-

• lactamase inducing activities were obtained by cefazolin (first generation cephalosporin) in E. coli 1048 and C. jreundii, recording the highest levels of induction 98-fold and 51.4-fold of the constitutive enzyme at concentrations of 20 and 1 IJ.g ml-1 respectively. In P. mirabilis and P. vulgaris 1753, amoxycillin was the most potent 13-lactamase inducer at concentration of 100 IJ.g mr 1 Cefamandole and cefuroxime (second generation cephalosporins) were the strongest inducers in P. aeruginosa and S. marcescens 921/79, respectively. On the other hand cefuroxime was poor 13-lactamase inducer•in both P. aeruginosa and E. coli 1048, while the lowest amounts of the induced enzyme were obtained by cefamandole, penicillin G and ceftazidime in C. jreundii, P. mirabilis and P. vulgaris 1753, respectively. In general, different levels of 13-lactamase induction by various • concentrations of structurally different 13-lactam antibiotics in these different