GWAS Study Applied to Phenotypically Slow Growth Strains of Listeria monocytogenes Workflow and Outcome

<i>Listeria monocytogenes</i> (<i>Lm</i>) is a serious public health foodborne pathogen cause of listeriosis, usually in elderly, pregnant and immunocompromised people, linked to consumption of contaminated food, especially ready-to-eat (RTE) products. Different protocols can be used to detect <i>Lm</i>, and ISO11290-1:2017 is the reference method in Europe. Through molecular techniques such as whole genome sequencing (WGS) it is possible to discriminate between <i>Lm</i> strains, which are unequally distributed between clinical cases, food or food related environments, probably also due to enrichment step bias towards some <i>Lm</i> serogroup (IIa) compared to IVb. In the present work a set of <i>Lm</i> strains, detected in clinical cases and food, was investigated to define <i>Lm</i> strains growth ability after incubation in Half Fraser broth, and Genome Wide Association Studies (GWAS) applied to correlate the growth phenotype traits to presence of relevant genes. GWAS enabled the identification of a more relevant cassette of genes associated to a holin region of bacteriophage A118 and the determination of the distribution of relevant genes, highlighted from GWAS analysis within a population of <i>Lm</i> IVb and IIa.