Phenotypic and Genotypic Comparison of Irish Sourced Listeria monocytogenes Isolates for Sanitiser Resistance and Low-Temperature Growth

This study investigates the genetic and phenotypic factors influencing Listeria monocytogenes in the context of sanitizer resistance and low-temperature growth, with a focus on isolates collected from Irish food processing facilities. The study begins by examining the presence of sanitizer resistance genes (mdrL, qacH, emrE, bcrABC) in 150 isolates, showing that isolates harboring bcrABC and qacH genes demonstrated significantly higher resistance to benzalkonium chloride (BAC) (P<0.05). However, no significant difference in BAC resistance was observed among isolates harboring both qacH and bcrABC genes. Additionally, environmental origins did not significantly affect MIC values across different processing facilities. The research further explored the growth dynamics of these isolates at 4°C and 7°C using five microbial growth models, identifying significant variability in growth rates among isolates. The Spline model exhibited greater variability and less reliability, leading to the selection of average growth rates from the other four models for further analysis. The study found that isolates from seafood environments exhibited higher growth rates at both temperatures compared to those from meat and mixed food environments. Moreover, the growth rate of isolates from vegetables increased more rapidly when the temperature was raised from 4°C to 7°C, compared to isolates from clinical settings, highlighting the influence of environmental factors on the growth behavior of L. monocytogenes in cold environments. Finally, this study investigates the genetic basis for low-temperature adaptation across different lineages and sequence types (STs). Lineage 2 isolates generally showed higher growth rates than lineage 1. Among the sequence types analyzed, ST has no practical effect on the growth ability of L. monocytogenes in low temperature environments. The study also considered 51 genes associated with cold resistance, but no direct correlation was found between gene identity ratios and growth rates. Linear regression analysis highlighted the gene mreB as significantly associated with growth rate variations. Additionally, treeWAS analysis identified significant single nucleotide polymorphisms (SNPs) within genes related to ribosomal protein modification, carbohydrate metabolism, and sugar transport, suggesting their potential roles in cold resistance. These findings contribute to a deeper understanding of the genetic and environmental factors that influence the resilience and growth of L. monocytogenes under stress conditions in food processing environments.