title: 'Covalent trapping' and latamoxef resistance in beta-lactamase-derepressed Pseudomonas aeruginosa.
abstract: Three Pseudomonas aeruginosa strains which constitutively produced chromosomal (Id, or Sabath and Abraham) beta-lactamase in large amounts were resistant to latamoxef (moxalactam) MICs, 128-256 mg/l). Their beta-lactamase-basal mutants, which produced 1200-18,000-fold less enzyme, were latamoxef-sensitive (MICs, 4-16 mg/l), suggesting that the enzyme caused the resistance of the parent organisms. Latamoxef was a feeble substrate of the enzyme (kcat less than 0.5/min) but reacted to form a stable complex that lacked catalytic activity against benzylpenicillin. The complex was isolated by gel filtration and was shown to be stable to isoelectric focusing, suggesting a covalent link between the enzyme and latamoxef. During incubation the complex underwent a slow breakdown, regenerating active enzyme. This breakdown obeyed first-order kinetics, and the half-life of the inactivated form was 19 +/- 1 min at 37 degrees C. Binding of antibiotic molecules in this complex may contribute to the latamoxef-resistance observed in the beta-lactamase-derepressed strains. This 'covalent trapping' should be distinguished from the 'non-covalent trapping' proposed elsewhere as a general mechanism of beta-lactamase-mediated resistance to reversibly-bound weak-substrate beta-lactams.
mesh_terms: D002509:Cephaloridine / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D009070:Moxalactam / Q000378:metabolism / Q000494:pharmacology*; D010400:Penicillin G / Q000378:metabolism; D010405:Penicillinase; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics
chemical_list: D010405:Penicillinase; D002509:Cephaloridine; D010400:Penicillin G; D009070:Moxalactam