Quaternary Ammonium Biocide Resistance in Non-Typhoidal Salmonella from Pig Carcasses

Non-typhoidal <i>Salmonella</i> (NTS) are one of the most common foodborne pathogens worldwide, and pork is a major food vehicle together with eggs and poultry meat. Contamination of pork within food processing facilities, such as slaughterhouses, can be associated with persistence of <i>Salmonella</i> in the environment due to biocide resistance. In this study, we assessed the susceptibility of NTS isolates from pig carcasses to a QAC-based commercial formulation according to the EN 1656/2009 standard and the presence of QAC resistance genes through PCR. The <i>qacEΔ1</i> and <i>qacF</i> genes were found in 31.8% and 29.5% of the isolates respectively, while <i>qacE</i> was absent. All isolates were found to be susceptible at a tested concentration 10 times lower (0.1%) than the minimum in-use recommended concentration, with MIC values below 0.1% (≈70 mg/L of Benzalkonium Chloride). Our findings point towards the importance of correct cleaning and disinfection protocols and the role of good hygiene practices as corrective and/or preventive measures to avoid cross-contamination.