title: Prevalence of the multiple antibiotic resistance operon (marRAB) in the genus Salmonella.
abstract: The multiple antibiotic resistance operon (marRAB) is a member of the multidrug resistance (mdr) systems. Similar to other mdr systems, this operon when induced encodes resistance to structurally and functionally unrelated antibiotics. marRAB has been shown to be conserved in the family Enterobacteriaceae, but within the genus Salmonella certain species appeared to be lacking this operon. To investigate how conserved the marRAB operon was in Salmonella, 30 veterinary isolates were examined by PCR, Southern blot, and dot blot analysis. Using DNA primers based on the marRAB operon of S. typhimurium, a predicted 2.3-kb amplicon resulted after PCR in 16 of the 30 organisms. The 2.3-kb DNA band from S. enteritidis was cloned and sequenced and shown to possess 99% sequence homology to marRAB from S. typhimurium. Using a labeled marRAB gene probe from S. enteritidis, Southern blot and dot blot analysis confirmed the presence of the operon in all 30 Salmonella species examined. Furthermore, when these isolates were induced with low levels of either tetracycline or chloramphenicol, increased antimicrobial resistance was observed to structurally and functionally unrelated antibiotics. Thus, the widespread occurrence of the marRAB locus in this genus prescribes judicious use of antimicrobials to avoid induction of a mdr phenotype.
authors.affiliation: Division of Biological Sciences, Emporia State University, 1200 Commercial, Box 4050, Emporia, KS 66801, USA.
authors.forename: N I
authors.initials: NI
authors.lastname: Kunonga
authors.forename: R J
authors.initials: RJ
authors.lastname: Sobieski
authors.forename: S S
authors.initials: SS
authors.lastname: Crupper
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D029968:Escherichia coli Proteins; D019450:Genes, MDR; D008826:Microbial Sensitivity Tests; D009876:Operon; D016133:Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics; D012475:Salmonella / Q000187:drug effects* / Q000235:genetics*; D012481:Salmonella Infections, Animal / Q000453:epidemiology / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C080002:MarA protein, E coli; C080004:MarR protein, E coli; D012097:Repressor Proteins; C080003:multiple antibiotic resistance protein B