title: ampC gene expression in promoter mutants of cefoxitin-resistant Escherichia coli clinical isolates.
abstract: Reverse transcriptase polymerase chain reaction was used to determine the amount of overexpression of the ampC gene in 52 cefoxitin-resistant Escherichia coli clinical isolates that had previously characterized mutations in their ampC promoter/attenuator regions. The results showed that mutations that create a consensus -35 box (TTGACA) are the most important factor in strengthening the ampC promoter, followed by base pair insertions that increase the distance between the -35 and -10 boxes to 17 or 18 bp. Mutations in the -10 box are of lesser importance and those in the attenuator region appear to have little effect on ampC expression. Three strains overexpress ampC due to the effect of insertion elements located in the ampC promoter regions. Further, the data show that there is no correlation between ampC overexpression and the minimum inhibition concentration of cefoxitin in clinical isolates. Overall, the data indicate that a combination of ampC promoter mutations and other strain-specific factors combine to contribute to the magnitude of cefoxitin resistance in E. coli.
authors.affiliation: National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, MB, Canada.
authors.forename: Dobryan M
authors.initials: DM
authors.lastname: Tracz
authors.forename: David A
authors.initials: DA
authors.lastname: Boyd
authors.forename: Romeo
authors.initials: R
authors.lastname: Hizon
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Bryce
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
authors.forename: Marianna
authors.initials: M
authors.lastname: Ofner-Agostini
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Simor
authors.forename: Shirley
authors.initials: S
authors.lastname: Paton
authors.forename: Michael R
authors.initials: MR
authors.lastname: Mulvey
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D002440:Cefoxitin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D002440:Cefoxitin; D001618:beta-Lactamases