title: Intrinsic mechanism decreases susceptibility of Escherichia coli O157:H7 to multiple antibiotics.
abstract: Chloramphenicol-resistant mutants of Escherichia coli O157:H7 (n = 52) demonstrated multiple resistance to tetracycline, nalidixic acid, and ciprofloxacin. Approximately half of the mutants approached the clinical level of resistance to the antibiotic tetracycline. Mutants demonstrated a wide range of sensitivity to each antibiotic; for tetracycline, some isolates demonstrated a twofold increase, whereas others demonstrated a 15-fold increase in resistance. Continuous exposure to chloramphenicol did not affect the growth of mutants, suggesting that mutation does not have a negative effect on cell survival. Complementation experiments with a functional marR restored antibiotic susceptibility of selected mutants to levels similar to wild-type strains, suggesting that mar mutation was responsible for the decrease in sensitivity. The multiple antibiotic resistance (mar) operon is a global regulator controlling intrinsic resistance toward structurally and functionally unrelated antibiotics and other noxious agents. Antimicrobial use in both human and agricultural practice should be administered in a manner to prevent selection of resistant mutants.
authors.affiliation: Cook College, Department of Food Science, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, New Jersey 08901-8520, USA.
authors.forename: Sherene S
authors.initials: SS
authors.lastname: Golding
authors.forename: Karl R
authors.initials: KR
authors.lastname: Matthews
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002701:Chloramphenicol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D005516:Food Microbiology; D005798:Genes, Bacterial / Q000235:genetics; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D016133:Polymerase Chain Reaction / Q000379:methods; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D002701:Chloramphenicol; D013752:Tetracycline