Co-resistance Mechanism Of Disinfectant And Cadmium In Food-borne Listeria Monocytogenes

Disinfectants, which play an important role in pathogenic bacteria control andprevention, are widely used in households, medical and food processing environments. Inrecent years, disinfectants resistance of food and environment associated bacterias isfrequently reported, raising extensive attention towards the problem of disinfectant resistance,and among which, the underlying mechanisms are of special concern. Listeria monocytogenes,a hazardous foodborne pathogen, can cause human listerisis mainly throughfoodscontaminated during the food processing process. Co-resistance of quaternaryammonium compounds (QACs) and heavy metal cadmium among L.monocytogenes wasfrequently reported in recent years. In this study, the underlying mechanisms of theco-resistant effect of benzalkonium chloride (BC) and cadmium in L.monocytogenes strainsare investigated.BC and cadmium resistance of food-borne L.monocytogenesstrains isolated from Hebeiprovince were detected.10strains (14.1%) were co-resistant to BC and cadmium.26.8%L.monocytogenes strains were resistant to BC, with resistance rate more remarkable amongstrains of serotype4b.49.3%L.monocytogenes strains were resistant to cadmium, withresistance rate more remarkable among strains of serotype1/2a (or3a).Resistant strains were subjected to detect the activity of efflux pump. The resultsshowed that among7out of19BC resistant strains and all of the35cadmium resistant strains,efflux pump played a role in conferring resistant effects.PCR amplification results showed that1strain carried qacA gene,7strains carriedqacE1△-sulgene;46strains carried cadA1gene, and3strains carriedcadA2gene. It is worthnoting that not all of the resistance determinants harboring strains exhibited resistantphenotype.A BC and cadmium resistant (BCrand Cdr) L.monocytoges strain (11GZL18) isolatedfrom raw pork in Guangzhou in2011were detected to carry both bcrABC and cadAC2.Plasmid curing experiment indicated that strain11GZL18harbored a BCrand Cdrplasmid.Further study showed that bcrABC and cadAC2genes co-existed in a plasmid, which can betransferred toEscherichia.colistrain by chemical and natural transferation and rendered it moreresistant to both BC and cadmium.bcrABC and its genetic environment were characterized. The results showed thatbcrABC and cadAC2genes were located on a novel plasmid. bcrABC and its neighboring21678nt nucleotide sequences exhibited99%identity with plasmid pLM80of L.monocytogenes strain H7858.In this study, co-resistance of BC and cadmium among foodborne L.monocytogeneswere detected. On the plasmid, a novel sequence harboring both bcrABC and cadAC2wascharacterized. The plasmid mediated the co-resistance effect of BC and cadmium through theharboring of both BC and cadmium resistance determinants. It was transferrable andfunctional and can render gram-negative E. coli strain DH5α more resistant to BC andcadmium.