Purpose: To elucidate the contribution of LGI1 to Lm survival in the food chain and virulence.
Methods: LGI1 function was studied using gene deletions, and real-time reverse-transcription polymerase chain reaction (16 coding regions). LGI1 genes with putative efflux (emrE), regulatory (lmo1851), and adhesion (sel1) functions were deleted in a clinical Lm 08-5578 strain using allelic exchange and pKSV7 vector. Isolates were exposed to acid (HCl, pH 2.5 - 4.5), cold (4°C), salt (10 - 20% NaCl), and quaternary ammonium compounds (QACs) in either brain-heart infusion or tryptic soy broth, and their survival and growth were measured. Adhesion and invasion of Caco-2 and HeLa cells of Δsel1 was compared to the parent strain, and other controls (EGD-SmR BUG5; 10403S). Differences in growth, and adhesion/invasion efficiencies were assessed using ANOVA with Dunnett’s test, at P < 0.05.
Results: Lm 08-5578 was highly tolerant to the tested stresses, with 14/16 LGI1 coding sequences induced in the presence of QAC benzalkonium chloride (5 μg/ml). The lmo1861 gene was constitutively expressed under all tested conditions (4°C, 37°C, 52°C, QACs, 0 - 30 UV). Deletion of lmo1851 and sel1 had no effect on the stress response and adherence/invasion, respectively, whereas deletion of the emrE gene resulted in the increased susceptibility to QACs (P < 0.05).
Significance: LGI1 appears tightly regulated. It was induced specifically in the presence of QACs, and increased Lm tolerance to these compounds. As such, this island improves survival and persistence of Lm in the food chain.