Listeria monocytogenes induced dysbiosis in snails and rebiosis achieved by administration of the gut commensal Lactobacillus plantarum Sgs14 strain

Listeria monocytogenes strains were isolated from Cornu aspersum maxima snails from farm units experiencing high mortalities and were characterized by phenotypic, molecular and biochemical criteria. A high heterogeneity was observed in the pulsed-field gel electrophoresis (PFGE) pulsotypes as well as in the virulence (13–100% mortality) among the fifteen L. monocytogenes strains. One strain was characterized as non-virulent while three strains exhibited hypervirulent phenotype. Hypervirulence activity was associated with cell surface properties such as hydrophobicity, autoaggregation and biofilm formation, with increased tolerance to snail's gut barriers such as pedal mucus, gastric mucus, gastric juices, and acidic pH as well as with increased capacity to resist the antibacterial activity of snail haemolymph and modulate immune cell populations and functions such as chemotaxis and phagocytoses. L. monocytogenes dysbiosis was characterized by a clinicopathological phenotype including immobilization of snails' headfoot outside the shell, increased mucus-secreting cells in the intestinal epithelium and feces, alteration of intestinal ridges morphology and excessive increase of haemolymph immune cells and cell death. Rebiosis in L. monocytogenes SN3 strain infected snails was achieved by dietary supplementation of the snail-gut commensal probiotic L. plantarum Sgs14 strain by exhibiting anti-Listeria activity, reducing mortality and clinicopathological manifestations as well as exhibiting immunomodulatory activity. •L. monocytogenes strains differ in their virulence capacity in snails.•Hypervirulent strains tolerate gut defense barriers, autoaggregate & form biofilms.•Hypervirulent strains alter haemolymph cell composition & inhibit phagocytoses.•Listeria gut dysbiosis alter intestinal ridges morphology and increase mucus cells.•Rebiosis is achieved by administration of snail-probiotic L. plantarum Sgs14 strain.