P2-197 emrE Gene Located on the Listeria Genomic Island 1 Encodes for an Efflux Pump That Contributes to Listeria monocytogenes Tolerance to Quaternary Ammonium Compounds

Monday, July 27, 2015
Exhibit Hall (Oregon Convention Center)
Jovana Kovacevic, University of British Columbia, Vancouver, Canada
Ewa Walecka-Zacharska, Wroclaw University of Environmental and Life Sciences, Wroclaw, Poland
Kevin Allen, University of British Columbia, Vancouver, Canada
David Kitts, University of British Columbia, Vancouver, Canada
Matthew Gilmour, University of Manitoba, Winnipeg, Canada
Introduction: Contamination of deli meats with Listeria monocytogenes (Lm) resulted in 57 cases of Listeriosis and 24 deaths in 2008 in Canada. Sequencing of the strains implicated in the outbreak (08-5578 and 08-5923) revealed the presence of a novel putative efflux pump (EmrELm) located on an uncharacterized 50 kb island, LGI1.

Purpose: To investigate the role of LGI1 encoded emrE in Lm tolerance to antimicrobials.

Methods: Non-polar emrELm deletion mutant (ΔemrELm) was created in Lm 08-5578 using allelic exchange and pKSV7 vector. Isolates were exposed to antimicrobials [benzalkonium chloride (BAC), E-San, ciprofloxacin, chloramphenicol, erythromycin, gentamicin, tetracycline, triclosan] and acriflavine dye, and their minimum inhibitory concentrations (MICs) were assessed with agar and microbroth dilution methods. Real-time reverse transcription PCR was used to measure transcript levels of emrELm, ldemdrLsigB, and putative LGI1 regulators (lmo1851, lmo1861) in Lm 08-5578 following 1 h exposure to BAC (10 μg/ml). Differences in the lag phase (LP; h), growth rate (GR; ΔOD600/h), and maximum optical density (MOD; OD600) of the parent and ΔemrELm (t-test), and genetically similar strains with (n = 8) and without LGI1 (n = 8; Mann-Whitney) were assessed at sub-lethal QACs concentrations (24 h, 30°C). 

Results: Increased transcription of lmo1861 (82.4-fold), emrE (49.6), sigB (4.1), and lmo1851 (2.3) was observed in the presence of BAC. Deletion of the emrE gene resulted in longer LP (P < 0.0001), and slower GR (P < 0.05) at sub-lethal QACs concentrations, and 2 - 3 times lower MICs; no change in MICs to other tested antimicrobials was observed. Shorter LP (P < 0.05), faster GR (P < 0.001), and higher MOD (P < 0.05) were seen for strains possessing LGI1 than those without LGI1. 

Significance: These data confirm the role of a novel Lm efflux pump, EmrE, in Lm tolerance to QACs. Since QAC sanitizers are commonly used in the food chain, there is a concern Lm strains possessing emrELm will have a survival advantage in food processing environments.