title: High incidence of multiple antibiotic resistant cells in cultures of in enterohemorrhagic Escherichia coli O157:H7.
abstract: The spontaneous incidence of chloramphenicol (Cam) resistant mutant bacteria is at least ten-fold higher in cultures of enterohemorrhagic Escherichia coli O157:H7 strain EDL933 than in E. coli K-12. It is at least 100-fold higher in the dam (DNA adenine methyltransferase) derivative of EDL933, compared to the dam strain of E. coli K-12, thereby preventing the use of Cam resistance as a marker in gene replacement technology. Genome sequencing of Cam-resistant isolates of EDL933 and its dam derivatives showed that the marR (multiple antibiotic resistance) gene was mutated in every case but not in the Cam-sensitive parental strains. As expected from mutation in the marR gene, the Cam-resistant bacteria were also found to be resistant to tetracycline and nalidixic acid. The marR gene in strain EDL933 is annotated as a shorter open reading frame than that in E. coli K-12 but the longer marR(+) open reading frame was more efficient at complementing the marR antibiotic-resistance phenotype of strain EDL933. Beta-lactamase-tolerant derivatives were present at frequencies 10-100 times greater in cultures of marR derivatives of strain EDL933 than the parent strain. Spontaneous mutation frequency to rifampicin, spectinomycin and streptomycin resistance was the same in E. coli O157:H7 and E. coli K-12 strains.
authors.affiliation: Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, United States.
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Carone
authors.affiliation: Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, United States.
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
authors.affiliation: Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA 01605, United States.
authors.forename: Kenan C
authors.initials: KC
authors.lastname: Murphy
authors.affiliation: Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, United States. Electronic address: martin.marinus@umassmed.edu.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Marinus
mesh_terms: D002228:Carbenicillin / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics; D005816:Genetic Complementation Test; D008826:Microbial Sensitivity Tests; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; C080004:MarR protein, E coli; D012097:Repressor Proteins; D002701:Chloramphenicol; D002228:Carbenicillin
keywords: DNA; Escherichia coli O157; Genes; Multiple antibiotic resistance; Mutation; Repressor protein