title: Overproduced beta-lactamase and the outer-membrane barrier as resistance factors in Serratia marcescens highly resistant to beta-lactamase-stable beta-lactam antibiotics.
abstract: In a clinical isolate of Serratia marcescens different states of low and high resistance to different beta-lactam antibiotics considered to be beta-lactamase-stable, viz. cefotaxime, ceftizoxime, ceftazidime, aztreonam, cefoxitin and imipenem, were found to be connected with the presence of constitutively overproduced, chromosomally encoded beta-lactamase at concentrations in the bacterial periplasm of 0.4 and 0.9 mM, respectively. All the antibiotics were degraded by the beta-lactamase. However, kinetic constants varied widely: k(m) from 92 to 0.012 microM and k(cat) from 3.4 to 2x10(-4)s(-1). The relative contributions to resistance by the functioning of periplasmic beta-lactamase, resynthesis of this enzyme, and limitation of antibiotic penetration by the bacterial outer membrane were analysed by computer simulations according to steady-state and non-steady-state models of interactions in the periplasm. Results for cefotaxime, ceftizomime, ceftazidime, aztreonam and latamoxef revealed overproduced beta-lactamase as the sole cause of the state of low resistance while antibiotic permeability was the same as in non-resistant S. marcescens strains. In contrast, high resistance was due to beta-lactamase action and decreased permeability of antibiotics. For resistance to aztreonam, only, immobilization of the antibiotic as covalent acyl-enzyme by newly synthesized beta-lactamase was essential. For cefoxitin, ampicillin and imipenem the analyses indicated that additional resistance factors may play a role, e.g. induction of beta-lactamase.
authors.affiliation: Institut für Mikrobiologie, Technische Hochschule, Darmstadt, FRG
authors.forename: U
authors.initials: U
authors.lastname: Hechler
authors.forename: M
authors.initials: M
authors.lastname: van den Weghe
authors.forename: H H
authors.initials: HH
authors.lastname: Martin
authors.forename: J M
authors.initials: JM
authors.lastname: Frère
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001398:Aztreonam / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D004352:Drug Resistance, Microbial; D004756:Enterobacteriaceae Infections / Q000188:drug therapy / Q000382:microbiology; D004790:Enzyme Induction; D015964:Gene Expression Regulation, Bacterial; D015378:Imipenem / Q000494:pharmacology; D007700:Kinetics; D012706:Serratia marcescens / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D065093:beta-Lactamase Inhibitors; D015378:Imipenem; D001618:beta-Lactamases; D001398:Aztreonam