title: Benzalkonium chloride and heavy-metal tolerance in Listeria monocytogenes from retail foods.
abstract: Phenotypic and genotypic tolerance in 71 Listeria monocytogenes isolates from different varieties of foods to benzalkonium chloride (BC) and cadmium were investigated by susceptibility test and molecular methods. To investigate the role of efflux pumps in BC tolerance, reserpine, an efflux pump inhibitor, was added to the BC tolerant strains. Tolerance to BC and cadmium were 26.8% (19/71) and 49.3% (35/71) respectively. Strains with BC tolerance were significantly more frequent among those of serotype 4b (100%, 6/6) than among those of serotype 1/2a (or 3a) (13.5%, 5/37), which represent the predominant number of strains (52.1%, 37/71). Tolerance to cadmium was encountered among 62.2% (23/37) and 50.0% (3/6) of the serotype 1/2a (or 3a) and 4b strains, respectively, and among 19.0% (4/21) of the strains of the serotype 1/2c. All of the 10 (14.1%) isolates found to be BC and cadmium co-tolerance were isolated from raw meat or quick-frozen food made of wheat flour and rice. Five multi-drug resistant strains were tolerant to cadmium as well. Among 71 isolates examined, one contained qacA and three contained qacEΔ1-sul. To the best of our knowledge, this is the first detection of qacA and qacEΔ1-sul in L. monocytogenes, an indication of the possible horizontal transfer of the two genes. Addition of reserpine to the tolerant strains resulted in the loss of tolerance among seven out of 19 BC strains, suggesting a certain role the efflux pump played in mediating BC tolerance. Of the three distinct cadA types known to date in L. monocytogenes, the cadA1 and cadA2 genes were detected among 24 (33.8%) and three (4.2%) isolates respectively. The presence of cadA1 and cadA2 largely corresponded to the susceptibility phenotype. A subset (9/35 [25.7%]) of the cadmium-tolerant isolates lacked the known cadmium resistance determinants. These findings suggest that food products could act as a reservoir for L. monocytogenes harboring tolerance to BC and cadmium and will further our understanding of the adaptations of this organism to these two compounds.
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, Guangdong, China.
authors.forename: Dongyang
authors.initials: D
authors.lastname: Xu
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, Guangdong, China.
authors.forename: Yanli
authors.initials: Y
authors.lastname: Li
authors.affiliation: Graduate School of Life and Environment Sciences, Osaka Prefecture University, Izumisano, Osaka 598-8531, Japan.
authors.forename: M Shamim Hasan
authors.initials: MS
authors.lastname: Zahid
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, Guangdong, China; Graduate School of Life and Environment Sciences, Osaka Prefecture University, Izumisano, Osaka 598-8531, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Yamasaki
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, Guangdong, China; Graduate School of Life and Environment Sciences, Osaka Prefecture University, Izumisano, Osaka 598-8531, Japan.
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.affiliation: Food Safety Key Lab of Liaoning Province, Bohai University, Jinzhou 121013, China. Electronic address: lijr6491@yahoo.com.cn.
authors.forename: Jian-rong
authors.initials: JR
authors.lastname: Li
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, Guangdong, China. Electronic address: yanhe@scut.edu.cn.
authors.forename: He
authors.initials: H
authors.lastname: Yan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001548:Benzalkonium Compounds / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005516:Food Microbiology; D006801:Humans; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000302:isolation & purification*; D019216:Metals, Heavy / Q000494:pharmacology*
chemical_list: D001426:Bacterial Proteins; D001548:Benzalkonium Compounds; D019216:Metals, Heavy
keywords: Benzalkonium chloride; Cadmium; Cadmium resistance determinants; Listeria monocytogenes; QAC resistance determinants; Tolerance