Three New Lactobacillus plantarum Strains in the Probiotic Toolbox against Gut Pathogen Salmonella enterica Serotype Typhimurium

Abstract

The benefits of probiotic bacteria have been widely explored. However, fermented foods and digestive system of humans and animals are an inexhaustible source of new potentially probiotic microorganisms. In this study we present three new Lactobacillus plantarum strains isolated from different dairy products: cow's cheese, sheep's cheese and whey. In order to determine the antibacterial activity of yet unexplored L. plantarum strains against Salmonella enterica serotype Typhimurium, in vitro competition and co-culture tests were done. Furthermore, adhesion of these strains to Caco-2 cells and their influence on the adhesion of Salmonella were tested. Results showed the potential probiotic activity of isolated strains. L. plantarum strains survived in the presence of 1% bile salts, they possessed acidification ability, antibacterial activity and significantly attenuated the growth of S. Typhimurium in brain heart infusion broth. All tested L. plantarum strains were able to adhere to Caco-2 cells and significantly impair the adhesion of S. Typhimurium. All three L. plantarum strains exhibited significant probiotic potential and anti-Salmonella activity; therefore, further testing on in vivo models should follow.

Keywords: Salmonella; antagonistic activity; mechanism of action; probiotic bacteria.

Fig. 1

The inhibitory activity of Lactobacillus plantarum strains A, B and S1 co-cultured with Salmonella Typhimurium (S.T.). Values are mean±standard deviations of the results from two separate experiments. Asterisk indicates differences between S.T.+A, S.T.+B and S.T.+S1 and the control at p<0.05

Fig. 2

Adhesion properties of Lactobacillus plantarum: a) adhesion of strains A, B and S1 to Caco-2 cells. Values are mean± standard deviation of the results from two separate experiments. Asterisk indicates differences between the tested groups at p<0.05; b) microphotographs (magnification of 1000×) show adhesion of L. plantarum strain A to the Caco-2 cells (arrows). Slides were stained with Giemsa stain

Fig. 3

Number of Salmonella Typhimurium (S.T.) bacteria adhered to Caco-2 cells, depending on the pretreatment and the simultaneous incubation with L. plantarum strains A, B and S1 (co-incubation) during 2 h of incubation. Mean values±standard deviations of at least three independent experiments are shown. Single asterisk indicates differences between S.T.+A, S.T.+B and S.T.+S1 and the control (S.T.), and two asterisks indicate differences among treated groups (S.T.+B) by ANOVA on ranks test at p<0.05