A multidrug resistance regulatory chromosomal locus is widespread among enteric bacteria

J Infect Dis. 1993 Aug;168(2):484-8. doi: 10.1093/infdis/168.2.484.


Constitutive expression of the mar operon (marRAB) in Escherichia coli produces a multiple antibiotic resistance phenotype mediated by the expression of multiple genetic loci in response to regulatory proteins in the operon. A mar-specific DNA probe was used to search for the operon in bacterial strains representing 53 species and 27 genera. Among these, 6 other Enterobacteriaceae, Salmonella, Shigella, Klebsiella, Citrobacter, Hafnia, and Enterobacter species, contained DNA sequences that hybridized to the probe under high-stringency conditions. By use of a selection protocol developed to obtain multiple antibiotic resistant mutants of E. coli, multiply resistant mutants that showed increased expression of mar-specific RNA were obtained from Enterobacter agglomerans and Salmonella species.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Northern
  • Blotting, Southern
  • Chromosomes, Bacterial*
  • DNA, Bacterial / analysis
  • DNA, Bacterial / genetics
  • Drug Resistance, Microbial / genetics
  • Enterobacteriaceae / drug effects*
  • Enterobacteriaceae / genetics*
  • Enterobacteriaceae Infections / microbiology
  • Mutation
  • Operon
  • Regulatory Sequences, Nucleic Acid
  • Salmonella / drug effects
  • Salmonella / genetics


  • DNA, Bacterial