Variability in Cold Tolerance of Food and Clinical Listeria monocytogenes Isolates

Abstract

The aim of this study was to investigate the level of strain variability amongst food and clinical Listeria monocytogenes isolates growing at low temperatures (4 and 7 °C) in both laboratory media and real food matrices. Isolates (n = 150) grown in laboratory media demonstrated a large variation in growth profiles measured using optical density. Overall, it was noted that clinical isolates exhibited a significantly higher growth rate (p ≤ 0.05) at 7 °C than the other isolates. Analysis of variance (ANOVA) tests of isolates grouped using Multi Locus Sequence Typing (MLST) revealed that clonal complex 18 (CC18) isolates were significantly (p ≤ 0.05) faster growing at 4 °C than other CC-type isolates while CC101, CC18, CC8, CC37 and CC14 were faster growing than other CC types at 7 °C. Euclidean distance and Ward method-based hierarchical clustering of mean growth rates classified 33.33% of isolates as faster growing. Fast and slow growing representative isolates were selected from the cluster analysis and growth rates were determined using plate count data in laboratory media and model food matrices. In agreement with the optical density experiments, CC18 isolates were faster and CC121 isolates were slower than other CC types in laboratory media, UHT milk and fish pie. The same trend was observed in chocolate milk but the differences were not statistically significant. Moreover, pan-genome analysis (Scoary) of isolate genome sequences only identified six genes of unknown function associated with increased cold tolerance while failing to identify any known cold tolerance genes. Overall, an association that was consistent in laboratory media and real food matrices was demonstrated between isolate CC type and increased cold tolerance.

Genomic characterization of Listeria monocytogenes recovered from dairy facilities in British Columbia, Canada from 2007 to 2017

“…However, SSI-1 was not highly prevalent among BC isolates, with only four isolates from the same facility (#71) possessing full length SSI-1 (Figure 3). Of particular interest, three of these isolates belonged to CC7, which has previously been shown to have a significantly higher tolerance to lactic acid compared to 14 other CCs studied by Myintzaw et al (2022). Other studies have also proposed the presence of SSI-1 aiding in biofilm formation and increased adherence (Keeney et al, 2018), and impacting quaternary ammonium compound tolerance (Bland et al, 2021), giving the isolates increased survival advantage in a facility.…”

Association of Virulence, Biofilm, and Antimicrobial Resistance Genes with Specific Clonal Complex Types of Listeria monocytogenes

“…In this study, all the Lineage II isolates, including CC20, CC18, CC26, CC9, CC7, and CC155, were predicted to contain more stress tolerance genes than Lineage I isolates ( Figure 4 ). Unsurprisingly, these CC-type isolates have been observed to grow faster in cold temperatures [ 3 ] and demonstrate increased tolerance to acetic and propionic acid [ 5 ]. This may explain why these CC-types were more prevalent in food and food processing environments with the presence of combinations of more stress tolerance genes.…”

“…The capability of L. monocytogenes to proliferate at lower temperatures [ 2 , 3 ] and lower pH [ 4 , 5 ], the resistance to commonly used disinfectants [ 6 ] in the food industry, and the ability to form biofilms [ 7 ] is primarily responsible for their stress survival and persistence. One of the key problems in microbial risk profiling is strain variation.…”

Persistence of microbiological hazards in food and feed production and processing environments

“…Myintzaw et al. (2023) identified the presence of bapL to be specific in CC121, CC14, CC204, CC9 and CC20, while inlL was exclusively present in CC155, CC26, CC37, CC18, CC204, CC20, CC412 and CC7.…”