Resistance to benzalkonium chloride and cadmium chloride in Listeria monocytogenes isolates from food and food-processing environments in southern Brazil.

Resistance to quaternary ammonium compounds such as benzalkonium chloride (BC) has been observed in many Listeria monocytogenes strains worldwide and is associated with cadmium chloride (CC) resistance. Therefore, the aims of this study were to evaluate the susceptibility to BC and CC, detect the presence of resistance genes, and investigate the possible role of efflux pumps in BC and CC resistance in L. monocytogenes isolates from food and food-processing environments in southern Brazil. All 50 L. monocytogenes isolates (100%) were resistant to BC, and 29 isolates (58%) were resistant to CC. According to the resistance genes (mdrL, lde, emrE, bcrABC, radC, qacA, qacC/D, qacH, qacEΔ1, cadA1, cadA2, cadA3, cadA4, and cadC), only the efflux pumps MdrL and Lde were identified in 12 (24%) and 33 (66%) isolates, respectively. The analysis of resistance to BC and CC in the presence of reserpine, an efflux pump inhibitor, showed that the resistance was not influenced by efflux pumps. This study confirmed a high profile of resistance to BC and CC in L. monocytogenes from food sources, and to the knowledge of the authors, this is the first report of the presence of efflux pumps MdrL and Lde in L. monocytogenes from Brazil.