Tolerance of Listeria monocytogenes to quaternary ammonium sanitizers is mediated by a novel efflux pump encoded by emrE

Jovana Kovacevic, Jennifer Ziegler, Ewa Wałecka-Zacharska, Aleisha Reimer, David D Kitts, Matthew W. Gilmour

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103 Citations (Scopus)


A novel genomic island (LGI1) was discovered in Listeria monocytogenes isolates responsible for the deadliest listeriosis outbreak in Canada, in 2008. To investigate the functional role of LGI1, the outbreak strain 08-5578 was exposed to food chain-relevant stresses, and the expression of 16 LGI1 genes was measured. LGI1 genes with putative efflux (L. monocytogenes emrE [emrELm]), regulatory (lmo1851), and adhesion (sel1) functions were deleted, and the mutants were exposed to acid (HCl), cold (4°C), salt (10 to 20% NaCl), and quaternary ammonium-based sanitizers (QACs). Deletion of lmo1851 had no effect on the L. monocytogenes stress response, and deletion of sel1 did not influence Caco-2 and HeLa cell adherence/invasion, whereas deletion of emrE resulted in increased susceptibility to QACs (P < 0.05) but had no effect on the MICs of gentamicin, chloramphenicol, ciprofloxacin, erythromycin, tetracycline, acriflavine, and triclosan. In the presence of the QAC benzalkonium chloride (BAC; 5 μg/ml), 14/16 LGI1 genes were induced, and lmo1861 (putative repressor gene) was constitutively expressed at 4 °C, 37 °C, and 52 °C and in the presence of UV exposure (0 to 30 min). Following 1 h of exposure to BAC (10 μg/ml), upregulation of emrE (49.6-fold), lmo1851 (2.3-fold), lmo1861 (82.4-fold), and sigB (4.1-fold) occurred. Reserpine visibly suppressed the growth of the ΔemrELm strain, indicating that QAC tolerance is due at least partially to efflux activity. These data suggest that a minimal function of LGI1 is to increase the tolerance of L. monocytogenes to QACs via emrELm. Since QACs are commonly used in the food industry, there is a concern that L. monocytogenes strains possessing emrE will have an increased ability to survive this stress and thus to persist in food processing environments.

Original languageEnglish
Pages (from-to)939-953
Number of pages15
JournalApplied and Environmental Microbiology
Issue number3
Early online date22 Jan 2016
Publication statusPublished - 1 Feb 2016


  • Acriflavine/pharmacology
  • Anti-Bacterial Agents/pharmacology
  • Anti-Infective Agents, Local/pharmacology
  • Bacterial Proteins/genetics
  • Benzalkonium Compounds/pharmacology
  • Caco-2 Cells
  • Canada/epidemiology
  • Drug Resistance, Bacterial/genetics
  • Food Handling/standards
  • Food-Processing Industry/standards
  • Genes, MDR
  • Genomic Islands
  • HeLa Cells
  • Humans
  • Listeria monocytogenes/drug effects
  • Listeriosis/epidemiology
  • Microbial Sensitivity Tests
  • Mutation
  • Quaternary Ammonium Compounds/pharmacology
  • Triclosan/pharmacology

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