Resistance to Biocides inListeria monocytogenesCollected in Meat-Processing Environments.
The emergence of microorganisms exerting resistance to biocides is a challenge to meat-processing environments. Bacteria can be intrinsically resistant to biocides but resistance can also be acquired by adaptation to their sub-lethal concentrations. Moreover, the presence of biocide resistance determinants, which is closely linked to antibiotic resistance determinants, could lead to co-selection during disinfection practices along the food chain, and select cross-resistant foodborne pathogens. The purpose of this work was to test the resistance of wild strains ofListeria monocytogenes, isolated from pork meat processing plants, toward benzalkonium chloride (BC), used as proxy of quaternary ammonium compounds. Furthermore, the expression of two non-specific efflux pumps genes (ldeandmdrL) under biocide exposure was evaluated.L. monocytogeneswere isolated from five processing plants located in the Veneto region (northeast of Italy) before and after cleaning and disinfection (C&D) procedures. A total of 45 strains were collected: 36 strains before and nine after the C&D procedures. Collected strains were typed according to MLST and ERIC profiles. Strains sampled in the same site, isolated before, and after the C&D procedures and displaying the same MLST and ERIC profiles were tested for their sensitivity to different concentrations of BC, in a time course assay. The expression of non-specific efflux pumps was evaluated at each time point by qPCR usingtufAgene as housekeeping. A differential expression of the two investigated genes was observed:ldewas found to be more expressed by the strains isolated before C&D procedures while its expression was dose-dependent in the case of the post C&D procedures strain. On the contrary, the expression ofmdrLwas inhibited under low biocidal stress (10 ppm BC) and enhanced in the presence of high stress (100 ppm BC). These findings suggests a possible role for C&D procedures to selectL. monocytogenespersisters, pointing out the importance of dealing with the identification of risk factors in food plants sanification procedures that might select more tolerant strains.
Dipartimento per la Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale delle VeneziePadova, Italy; Department of Animal Medicine, Production and Health, University of PaduaPadova, Italy.
Daniele
D
Conficoni
Dipartimento per la Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale delle Venezie Padova, Italy.
Carmen
C
Losasso
Dipartimento per la Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale delle Venezie Padova, Italy.
Enzo
E
Cortini
Microbial Ecology Group, National Research Council - Institute of Ecosystem Study (CNR-ISE) Verbania, Italy.
Andrea
A
Di Cesare
Dipartimento per la Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale delle Venezie Padova, Italy.
Veronica
V
Cibin
Department of Animal Medicine, Production and Health, University of Padua Padova, Italy.
Valerio
V
Giaccone
Microbial Ecology Group, National Research Council - Institute of Ecosystem Study (CNR-ISE) Verbania, Italy.
Gianluca
G
Corno
Dipartimento per la Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale delle Venezie Padova, Italy.
Antonia
A
Ricci
Listeria monocytogenes; efflux pumps; environment; food-processing plants; gene expression; resistance genes