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Genomic associations of Listeria monocytogenes adhesion at 8°C Mahoney, David Burke James


Listeria monocytogenes, a highly virulent foodborne pathogen, remains a threat to the food system and has led to numerous foodborne outbreaks worldwide. L. monocytogenes can establish itself in food production facilities by adhering to surfaces, resulting in increased resistance to environmental stressors. The aim of this study was to evaluate the adhesion ability of a collection of L. monocytogenes at 8°C and to analyse associations between the observed phenotypes and genetic factors such as internalin A (inlA), stress survival islet 1 (SSI-1), and clonal complex (CC). L. monocytogenes isolates (n=184) were grown at 8°C and 100% relative humidity. Growth was determined by measurement of optical density at 600 nm. Adherent cells were stained using crystal violet and quantified spectrophotometrically at 595 nm. Genotyping of inlA and SSI-1, multi-locus sequence typing, and a genome wide association were performed to elucidate the phenotype-genotype relationships in L. monocytogenes cold adhesion. Among all inlA genotypes, truncated inlA isolates had the highest mean adhered cells (ANOVA; P<0.05), while isolates with the three-codon deletion inlA had the least mean adhered cells (ANOVA; P<0.05). When SSI-1 was present, more cells were adhered; and less cells were adhered when SSI-1 was absent (Welch’s t-test; P<0.05). Increased adhesion was associated with clonal complexes with low clinical frequency while lack of adhesion was associated with clonal complexes with high clinical frequency. A genome wide association study revealed genes which were not previously known to be associated with 8°C adhesion. The associations of genotype and 8°C adhesion suggests that there may be an evolutionary trade off between virulence and adhesion in L. monocytogenes.

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