Exposure of Salmonella enterica serovar 1,4, [5],12:i:- to benzalkonium chloride leads to acquired resistance to this disinfectant and antibiotics.

Abstract

Disinfectants such as benzalkonium chloride (BC) extensively used in animal farms and food-processing industries contribute to the development of adaptive- and cross-resistance in foodborne pathogens, posing a serious threat to food safety and human health. The purpose of this study is to explore whether continuous exposure of Salmonella enterica serovar 1,4, [5],12: i:- (S. 1,4, [5],12: i:-) to sublethal concentrations of BC could result in acquired resistance to this agent and other environmental stresses (e.g. antibiotics, heat, and acid). BC tolerance increased in all tested strains after exposure to gradually increasing concentrations of BC, with increases in minimum inhibitory concentrations between two and six-fold. The survival rate of BC-adapted strains was significantly (P<0.05) higher than that of their wild-type (non-adapted) counterparts in lethal concentrations of BC. In addition, significant reductions (P<0.05) in zeta potential were observed in BC-adapted strains compared to wild-type ones, indicating that reduction in cell surface charge was a cause of adaptative resistance. More importantly, two BC-adapted strains exhibited increased antibiotic resistance to levofloxacin, ceftazidime, and tigecycline, while gene mutations (gyrA, parC) and antibiotic efflux-related genes (acrB, mdsA, mdsB) were detected by genomic sequencing analysis. Moreover, the tolerance of BC-adapted strains to heat (50, 55, and 60°C) and acid (pH 2.0, 2.5) was strain-dependent and condition-dependent. Repeated exposure to sublethal concentrations of BC could result in the emergence of BC- and antibiotic-resistant S. 1,4, [5],12: i:- strains.