IN-VITRO ACTIVITY OF CEFPIROME AGAINST BETA-LACTAMASE-INDUCIBLE AND STABLY DEREPRESSED ENTEROBACTERIACEAE

Most members of the Enterobacteriaceae and Pseudomonas aeruginosa poss ess an inducible chromosomal class I beta-lactamase. Bacterial strains which produce high levels of beta-lactamase constitutively can be iso lated from infections; these derepressed mutants are responsible for r esistance to third-generation cephalosporins and ureidopenicillins. Mi nimum inhibitory concentrations of cefpirome, a fourth-generation ceph alosporin, and other beta-lactam antibiotics were determined for a ser ies of mutants of Citrobacter freundii, Enterobacter cloacae, Morganel la morganii, Proteus vulgaris and Serratia marcescens with inducible s tably derepressed or basal expression of chromosomal class I beta-lact amases. All the antibiotics tested were almost equally active against beta-lactamase-inducible organisms and their basal mutants. Imipenem a nd cefpirome showed better activity against derepressed mutants than t hird-generation cephalosporins and ureidopenicillins.