In vitro activity of cefpirome against beta-lactamase-inducible and stably derepressed enterobacteriaceae

Most members of the Enterobacteriaceae and Pseudomonas aeruginosa possess an inducible chromosomal class I β-lacta-mase. Bacterial strains which produce high levels of β-lacta-mase constitutively can be isolated from infections; these de-repressed mutants are responsible for resistance to third-gen-eration cephalosporins and ureidopenicillins. Minimum inhibitory concentrations of cefpirome, a fourth-generation cephalosporin, and other β-lactam antibiotics were determined for a series of mutants of Citrobacter freundii, Enterobacter cloacae, Morganella morganii, Proteus vulgaris and Seiratia marcescens with inducible stably derepressed or basal expression of chromosomal class I β-lactamases. All the antibiotics tested were almost equally active against β-lactamase-inducible organisms and their basal mutants. Imipenem and cefpirome showed better activity against derepressed mutants than third-generation cephalosporins and ureidopenicillins. © 1994 S. Karger AG, Basel.