Genotypes Associated with Listeria monocytogenes Isolates Displaying Impaired or Enhanced Tolerances to Cold, Salt, Acid, or Desiccation Stress

The human pathogen is a large concern in the food industry where its continuous detection in food products has caused a string of recalls in North America and Europe. Most recognized for its ability to grow in foods during refrigerated storage, can also tolerate several other food-related stresses with some strains possessing higher levels of tolerances than others. The objective of this study was to use a combination of phenotypic analyses and whole genome sequencing to elucidate potential relationships between genotypes and food-related stress tolerance phenotypes. To accomplish this, 166 isolates were sequenced and evaluated for their ability to grow in cold (4°C), salt (6% NaCl, 25°C), and acid (pH 5, 25°C) stress conditions as well as survive desiccation (33% RH, 20°C). The results revealed that the stress tolerance of is associated with serotype, clonal complex (CC), full length profiles, and the presence of a plasmid which was identified in 55% of isolates. Isolates with full length exhibited significantly ( < 0.001) enhanced cold tolerance relative to those harboring a premature stop codon (PMSC) in this gene. Similarly, isolates possessing a plasmid demonstrated significantly ( = 0.013) enhanced acid tolerance. We also identified nine new sequence types, a new PMSC, and several connections between CCs and the presence/absence or variations of specific genetic elements. A whole genome single-nucleotide-variants phylogeny revealed sporadic distribution of tolerant isolates and closely related sensitive and tolerant isolates, highlighting that minor genetic differences can influence the stress tolerance of . Specifically, a number of cold and desiccation sensitive isolates contained PMSCs in σ regulator genes ( ). Collectively, the results suggest that knowing the sequence type of an isolate in addition to screening for the presence of full-length and a plasmid, could help food processors and food agency investigators determine why certain isolates might be persisting in a food processing environment. Additionally, increased sequencing of isolates in combination with stress tolerance profiling, will enhance the ability to identify genetic elements associated with higher risk strains.