title: [The antibiotic agent azthreonam: studies on plasmid-dependent resistance formation].
abstract: Two mechanisms can be assumed that are responsible for the stability of azthreonam against the attack of beta-lactamases: first, azthreonam lacks binding to the enzyme protein and second, rate of hydrolysis is extremely low, resulting even in inhibition of enzyme activity. Enzyme kinetics were studied from highly purified enzymes: azthreonam did not bind to the TEM-1 enzyme, whereas the compound revealed a time-dependent inhibition of the chromosomally mediated Enterobacter cloacae enzyme. With various cephalosporins as substrates marked discrepancies in the mode of inhibition were observed: cefacedone revealed merely noncompetitive inhibition, cefazolin and cefoperazone demonstrated mixed-inhibition kinetics, and with cephalothin as the substrate enzyme kinetics strongly suggested binding of a second azthreonam molecule. With cefacedone as the substrate KI was ascertained to be 0.8 X 10(-7) mol/l. Conjugative transfer of the TEM-mediating plasmids R6K and RP1 resulted in 20 to 50-fold increase of the MIC's for the Enterobacter cloacae and Citrobacter freundii recipients, in spite of the fact that azthreonam does not serve as a substrate for the TEM-1 enzyme. These findings have likely to be attributed to an impaired penetration of the compound through the "outer membrane" of the recipient strains.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001398:Aztreonam; D004352:Drug Resistance, Microbial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology; D004926:Escherichia coli / Q000187:drug effects; D010957:Plasmids / Q000187:drug effects*; D001618:beta-Lactamases / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001618:beta-Lactamases; D001398:Aztreonam
vernacular_title: Das Antibiotikum Azthreonam: Untersuchungen zur plasmidbedingten Resistenzausbildung.