# Benzalkonium Chloride Tolerance Among Listeria innocua from Food and Food Processing Environments in Poland

## TL;DR

This study examines how Listeria innocua bacteria from food and processing environments in Poland tolerate the disinfectant benzalkonium chloride.

## Contribution

The study identifies the prevalence of BC tolerance and associated genes in L. innocua isolates from Polish food sources.

## Key findings

- MIC values for benzalkonium chloride ranged from 15 to 30 µg/mL on BHI agar and 5–20 µg/mL on blood-supplemented M-H agar.
- The qacH gene was the most prevalent (29%) among tolerance-associated genes in L. innocua isolates.

## Abstract

Benzalkonium chloride (BC) is widely used as a disinfectant in the food industry; however, increasing reports of Listeria innocua isolates exhibiting tolerance to this compound highlight the need to better understand their adaptive mechanisms. This study aimed to evaluate BC tolerance in 51 L. innocua isolates originating from raw and processed meat products (n = 32) and meat-processing environments in Poland (n = 19). Phenotypic tolerance was assessed using the agar diffusion method on two media: Brain Heart Infusion (BHI) agar and Mueller–Hinton (M-H) agar supplemented with 1.2% sheep blood, across BC concentrations of 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 µg/mL, allowing the determination of minimum inhibitory concentrations (MICs). Genotypic analysis of tolerance determinants (brcABC, ermC, qacE, qacF, qacG, qacH, and qacJ) was performed by PCR. On BHI agar, MIC values ranged from 15 to 30 µg/mL, with 15 µg/mL most frequently observed, whereas on blood-supplemented M-H agar, MICs were lower (5–20 µg/mL), most commonly 10 µg/mL. Among tolerance-associated genes, qacH was the most prevalent (29% of isolates), followed by brcABC (4%) and ermC (2%), while the remaining genes were absent. These findings suggest that food products may serve as a reservoir for L. innocua isolates harboring tolerance to BC and contribute to a deeper understanding of how this species adapts to quaternary ammonium compounds.