title: Contribution of chromosomal beta-lactamases to beta-lactam resistance in enterobacteria.
abstract: The two most important factors determining the level of beta-lactam resistance to novel cephalosporins in gram-negative enterobacteria are the chromosomal class C beta-lactamases, which have high affinity for these compounds, and the outer membrane permeability barrier. The individual importance of these factors and the interactions between them are discussed. Wild-type strains carry a chromosomal gene, ampC, encoding class C beta-lactamases. Expression from this gene is normally low, but it can in some species be induced by beta-lactam agents and related compounds. The current knowledge on the molecular mechanism governing both inducible and constitutive beta-lactamase synthesis is reviewed. Insight into these mechanisms explains why mutations leading to high-level enzyme over-production and beta-lactam resistance are much more frequent in species with a normally inducible beta-lactamase gene than in other gram-negative bacteria.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002876:Chromosomes, Bacterial; D002954:Citrobacter / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D004352:Drug Resistance, Microbial; D004754:Enterobacter / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D004790:Enzyme Induction; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D005798:Genes, Bacterial; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000235:genetics; D012760:Shigella / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases