Objective: The aim of this study was to test the inhibitory effect of supernatants of broth cultures of Bifidobacterium longum BB536 and Lactobacillus rhamnosus HN001, both individually and in combination, against Gram-negative strains (uropathogens, enteropathogens and a reference strain). Moreover, in vitro protection of B. longum BB536 and L. rhamnosus HN001, both individually and in combination, against pathogen adhesion to HT-29 cell line, was investigated.
Materials and methods: The inhibitory activity was performed by the agar diffusion test and in vitro antagonistic activity against pathogen adhesion to human epithelial intestinal HT-29 cells was performed using standardized culture techniques.
Results: The study showed that B. longum BB536 and L. rhamnosus HN001, individually and in combination have inhibitory activity against the majority of the Gram negative strains tested. Furthermore, the results showed that both probiotic strains have a good capacity to inhibit pathogenic adhesion to HT-29 cells. Moreover, the ability of B. longum BB536 and L. rhamnosus HN001 to inhibit pathogenic adhesion increased when they were used in combination.
Discussion: The combination of B. longum BB536 and L. rhamnosus HN001 showed inhibitory activity against Gram-negatives and an improved ability to reduce their adhesion properties and to compete with them.
Conclusions: The simultaneous presence of the two-probiotic strains could promote competitive mechanisms able to reduce the adhesion properties of pathogen strains and have an important ecological role within the highly competitive environment of the human gut.