Benzalkonium chloride tolerance of Listeria monocytogenes strains isolated from a meat processing facility is related to presence of plasmid-borne bcrABC cassette
Listeria monocytogenes is a serious foodborne pathogen capable of persisting in food processing environments. Tolerance to disinfectants used in industrial settings constitutes an important factor of Listeria survival. In the present study, the mechanism of tolerance to benzalkonium chloride (BAC) was investigated in 77 L. monocytogenes isolates from a meat facility. By PCR approach, the mdrL and lde chromosomal efflux pump genes were detected in all isolates. No isolate was positive for qacH and emrE genes. However, the bcrABC cassette was present in 17 isolates of serogroup IIa possessing the same AscI/ApaI pulsotype, the operon being localized on a plasmid. The significant relation of BAC tolerance with bcrABC presence was confirmed as all bcrABC positive isolates showed the highest minimal inhibitory concentration (MIC) values for BAC and increased sensitivity to BAC was observed after plasmid curing. No effect of the efflux pump inhibitor reserpine on BAC tolerance in bcrABC positive strains was observed in contrast to all bcrABC negative strains. Lower ethidium bromide efflux in bcrABC positive isolates compared to bcrABC negative and plasmid-cured L. monocytogenes isolates was observed. The expression of bcrABC genes was BAC-induced. The confirmed effect of bcrABC to increased BAC tolerance, coupled with its plasmid location, may be an important factor in potential dissemination of the biocide resistance among Listeria species. The understanding of molecular mechanisms of biocide tolerance should help to improve control measures to prevent further spread of L. monocytogenes in food production environments with frequent use of BAC.
KeywordsListeria monocytogenes Benzalkonium chloride tolerance Efflux pumps bcrABC casette
This work was supported by Slovak Research and Development Agency under the contract No. APVV-0498-12, by the VEGA Grant of the Ministry of Education of the Slovak Republic No. 1/0793/16 and by the project ITMS 26240120027 from OPRaD funded by the ERDF. We thank to Dr. Taurai Tasara from Institute für Lebensmittelsicherheit und Hygiene Universität Zürich for the provision of DNAs isolated from L. monocytogenes strains used as reference for PCR detection of emrE and qacH genes.
Conflict of interest
No conflict of interest declared.
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