Bacteriocin production as a mechanism for the antiinfective activity of Lactobacillus salivarius UCC118

Abstract

The mechanisms by which probiotic strains enhance the health of the host remain largely uncharacterized. Here we demonstrate that Lactobacillus salivarius UCC118, a recently sequenced and genetically tractable probiotic strain of human origin, produces a bacteriocin in vivo that can significantly protect mice against infection with the invasive foodborne pathogen Listeria monocytogenes. A stable mutant of Lb. salivarius UCC118 that is unable to produce the Abp118 bacteriocin also failed to protect mice against infection with two strains of L. monocytogenes, EGDe and LO28, confirming that bacteriocin production is the primary mediator of protection against this organism. Furthermore, Lb. salivarius UCC118 did not offer any protection when mice were infected with a strain of L. monocytogenes expressing the cognate Abp118 immunity protein AbpIM, confirming that the antimicrobial effect is a result of direct antagonism between Lb. salivarius and the pathogen, mediated by the bacteriocin Abp118.

Fig. 1.

In vivo protection against L. monocytogenes EGDe infection in livers and spleens after oral dosing of A/J mice with lactobacilli, Lactococcus, or bifidobacteria for 3 days before listerial infection. ∗, P < 0.05, indicating the statistically significant difference between the numbers of bacteria infecting organs compared with placebo-fed control mice (n = 4).

Fig. 2.

Probiotic dosing of A/J mice with UCC118 reduces the level of subsequent L. monocytogenes infection. (a) Whole livers dissected from A/J mice fed probiotic Lb. salivarius UCC118 for 6 days before oral infection with luminescent L. monocytogenes EGDe:pPL2lux-PhlyA. Livers of UCC118-fed animals display minimal amounts of luminescence compared with those of placebo-fed mice. (b) Livers (from a) and spleens of probiotic-fed mice (open bars) are significantly less infected than organs of placebo-fed mice (filled bars). ∗, P < 0.01 compared with placebo (n = 5).

Fig. 3.

Analysis of dosing regime. Lb. salivarius UCC118 was given orally to A/J mice for 3 days including day of infection (lane 1); 3 days before and 3 days after infection (lane 2); on the day of infection and 3 days after infection (lane 3); 2 days before infection (lane 4); and on the day of infection only (lane 5). Because of the large number of animals involved, each feeding trial was conducted with a placebo control, and results are expressed as the percentage of infection. Identical lowercase letters a–c denote no significant difference, and different letters denote a statistically significant difference (P < 0.05; n = 5).

Fig. 4.

Bacteriocin production mediates Lb. salivarius UCC118 protection against L. monocytogenes infection of A/J mice. A/J mice fed PBS placebo (filled bars), Lb. salivarius UCC118 (open bars), or UCC118Δabp118 (Bac⁻) (gray bars) for 3 days before infection with L. monocytogenes EGDe, L. monocytogenes LO28, or S. typhimurium UK1. Because of the large number of animals involved, each feeding trial was conducted with a placebo control, and results are expressed as the percentage of infection. Identical lowercase letters a and b denote no significant difference, and different letters denote a statistically significant difference (P < 0.001; n = 5).

Fig. 5.

Immunity to Abp118 overcomes the protective effect of UCC118. (a) Confirmation of immune phenotype of L. monocytogenes EGDe(abpIM) by using an agar-diffusion assay. L. monocytogenes LO28 and L. monocytogenes EGDe are susceptible to the Abp118 bacteriocin. (b) A/J mice fed PBS placebo, Lb. salivarius UCC118, or UCC118Δabp118 for 3 days before infection with L. monocytogenes EGDe(abpIM).