Co-resistance Mechanism Of Heavy Metal And Benzalkonium Chloride In Food-borne Listeria Spp.

Listeria monocytogenes,a hazardous foodborne pathogen,can cause human listerisis mainly through foods contaminated during the food processing process.Listeria innocua was recognized as a reservoir of antibiotic resistance for L.monocytogenes.Co-resistance of heavy metal cadmium and quaternary ammonium compounds among L.monocytogenes was frequerntly reported in recent years.In this study,tolerance in L.monocytogenes and L.innocua isolates from different varieties of foods to heavy metal and benzalkonium chloride(BC)were investigated.Cadmium,arsenic and BC resistance of food-borne L.monocytogenes and L.innocua isolated from Guangzhou and Xiamen were detected.Tolerance to Cadmium,arsenic and BC for L.monocytogenes were 90.0%,3.3% and 16.7%.Tolerance to Cadmium,arsenic and BC for L.innocua were 88.9%,0% and 33.3%.All BC-resistant strains were also resistant to cadmium,although the reverse was not always the case.BC resistant strains were subjected to detect the activity of efflux pump.The results showed that among all BC resistant strains,difference efflux pumps played a role in conferring resistant effects.PCR amplification results showed that 4 strains carried cadA1,18 strains carried cadA2,1 strain carried cadA4,arsA1 and arsA2 among 30 L.monnocytogens;2 strains carried cadA1,6 strains carried cadA2 among 27 L.innocua.Not QACs resistance determinants were detected in both L.monnocytogens and L.innocua.It is worth noting that 4 out of 5 BC resistant L.monnocytogens carried cadA2.In this study,we characterized a cadmium tolerance cassette and arsenic tolerance cassette harbored by a 35-kb genomic island in Listeria monocytogenes LM3,a strain isolated from raw meat in 2012.Phenotypic and genotypic tolerance in LM3 to Cd and As were investigated by susceptibility test and molecular methods.The result show that LM3 had an MIC of 70 ?g/ml for Cd and was suspected to As.The Cd and As tolerance cassette and its flanking sequence were characterized,with a total of 36,629 bp nucleotide sequence obtained.The 35-kb genomic island in strain LM3 exhibited 99.8% identity to that on strain LM Scott A.In this study,we found BC-resistant strains were also resistant to cadmium and a cadmium tolerance cassette and arsenic tolerance cassette harbored by a 35-kb genomic island in Listeria monocytogenes LM3.