Stress survival islet 1 contributes to serotype-specific differences in biofilm formation in Listeria monocytogenes

Listeria monocytogenes has a significant impact on the food industry by forming biofilms on food-processing equipment. Tandem analysis of whole-genome sequencing data with biofilm data from 166 environmental and food-related L. monocytogenes isolates has revealed serotypic and genetic factors that strongly correlate with adherence and biofilm formation, such as lineage, plasmid harbourage, a three-codon deletion in inlA and the presence of the stress survival islet 1 (SSI-1). Strains from serotype 1/2b, the majority of which contained SSI-1, formed the strongest biofilms, while serotype 4b strains, the majority of which did not contain SSI-1, formed the weakest biofilms. When serotype 1/2a was separated by its SSI-1 genotype, SSI-1-positive 1/2a strains demonstrated significantly higher capacity for biofilm formation after 3 days of growth at 30°C (P < 0·0001). Together, these findings indicate that SSI-1 may contribute to serotype-associated differences in the biofilm-forming capacity in L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: Parallel analysis of whole-genome sequences and serotype-specific data was performed to identify genetic markers that correlate with increased adherence and biofilm formation in L. monocytogenes. The analyses revealed the hitherto unrecognized role of SSI-1 in biofilm formation, contributing to deeper understanding of genetic factors that influence behaviour of the species in the food processing environment..