Protective effect of Lactobacillus sakei against experimental challenge with Listeria monocytogenes in gnotobiotic mice.

FELIPE HENRIQUE DA SILVA BAMBIRRA; KATIA GIANNI DE CARVALHO LIMA; BERNADETTE DORA GOMBOSSY DE MELO FRANCO; REGINA NARDI; FLAVIO HENRIQUE BARBOSA; JACQUES NICOLI

Tucuman, Argentina

Simposio; II International Symposium on Lactic Acid Bacteria; 2006

Probiotics are defined as viable microorganisms, which when ingested in adequate amount show beneficial effects for the host. A Lactobacillus sake isolated from sausage and presenting an in vitro antagonistic activity against Listeria monocytogenes Scotch A was tested for a possible protective effect in gnotobiotic mice experimentally challenged with the pathogenic bacteria. In the experimental group, germ-free mice (n=8) were inoculated intragastrically with 0.1 ml of the L. sake culture grown during 18 h in MRS broth (108 cfu).Four days after the monoassociation, when high population levels of L. sake were counted in the feces (109 cfu/ g of contents), the animals were challenged intragastrically with 0.1 ml of a suspension containing 108 cfu of L. monocytogenes (18 h incubation in BHI broth). Control group (n=8) was only challenged with the bacterial pathogen. Fecal counts showed that L. monocytogenes reached similar population levels of about 109 cfu/g of contentsin both group. After challenge, L. sake maintained the same fecal levels than before the pathogenic inoculation. However, animals in the control group showed a lower survival frequency (50%) when compared to the experimental one (100%). Concluding, a protective effect of L. sake against L. monocytogenes was demonstrated in vivo, but this phenomenon was not due to the antagonistic activityobserved in vitro. Other mechanisms are probably responsible for this protection such as competition for nutrients, competition for adhesion sites and/or immunomodulation.