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

## TL;DR

This study examines how Salmonella from pig carcasses resist a disinfectant and finds that despite resistance genes, they remain susceptible at low concentrations, highlighting the importance of proper hygiene.

## Contribution

The study reveals that Salmonella isolates with resistance genes are still susceptible to low concentrations of QAC disinfectants, challenging assumptions about biocide resistance.

## Key findings

- Salmonella isolates with resistance genes (qacEΔ1 and qacF) were susceptible to QAC disinfectants at 10 times lower concentrations than recommended.
- Correct cleaning and disinfection practices are critical to prevent Salmonella persistence in food processing environments.
- The absence of qacE gene in isolates suggests variability in resistance mechanisms among Salmonella strains.

## Abstract

In this study, we assessed the resistance ability of Salmonella isolated from pig carcasses to a commercial quaternary ammonium compound (QAC) disinfectant formulation and examined the prevalence of genes that are associated with such resistance and with possible persistence in the contaminated surfaces. Our results show that though the isolates carried resistance genes, they were susceptible to the disinfectant formulation, even at concentrations 10 times lower than the minimum recommended in-use concentration. These results show that the possible persistence of these bacteria in the environment of food processing facilities, such as slaughterhouses, should not be exclusively associated with disinfectant resistance, stressing the importance of correct cleaning and disinfection procedures and/or hygiene practices.

Non-typhoidal Salmonella (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 Salmonella 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 qacEΔ1 and qacF genes were found in 31.8% and 29.5% of the isolates respectively, while qacE 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.