In vitro inhibitory activity of Bifidobacterium longum BB536 and Lactobacillus rhamnosus HN001 alone or in combination against bacterial and Candida reference strains and clinical isolates

Rosanna Inturri,Laura Trovato,Giovanni Li Volti,Salvatore Oliveri,Giovanna Blandino

doi:10.1016/j.heliyon.2019.e02891

Abstract

Bifidobacterium longum BB536 and Lactobacillus rhamnosus HN001 are two strains frequently used as probiotic components in food supplements. The decrease of potentially pathogenic gastrointestinal microorganisms is one of their claimed mechanisms. The aim of this study was to investigate their ability, alone or in combination, to inhibit in vitro the growth of Gram-negative, Gram-positive and Candida reference strains and clinical isolates, using different methods.The cell-free supernatants were obtained by centrifugation and filtration from single or mixed broth cultures and the inhibitory activity was tested using both agar-well diffusion and broth microdilution methods. In order to get some preliminary information about the chemical nature of the active metabolites released in the supernatants, the inhibitory activity was investigated after neutralization, heat and proteolytic treatments.The highest inhibitory activity was shown by the untreated supernatant obtained from broth culture of the two probiotic strains, especially against bacterial reference strains and clinical isolates. This supernatant showed inhibitory activity towards Candida species, too. A decreased inhibitory activity was observed for the supernatants obtained from single cultures and after proteolytic treatment, against bacterial reference strains.The study suggests that the combination of B. longum BB536 and L. rhamnosus HN001 could represent a possible alternative against gastrointestinal and urinary pathogens either as prophylaxis or as treatment.

Highlights

The claimed effects of Bifidobacterium longum BB536 and Lactobacillus rhamnosus HN001 are: healthy balance of intestinal bacteria and gut health, respectively [1, 2]
Several studies have demonstrated that bifidobacteria and Lactic Acid Bacteria (LAB) are able to competitively exclude pathogenic bacteria and yeasts, either directly, through interactions with pathogenic strains, or indirectly, through the production of active metabolites and the induction of host immune defense [33, 35]
From a probiotic research concept, several studies have demonstrated the antimicrobial activity of supernatant obtained from broth cultures of probiotic strains but few studies have reported effects due to supernatants obtained from co-cultured probiotic strains

Summary

Introduction

The claimed effects of Bifidobacterium longum BB536 and Lactobacillus rhamnosus HN001 are: healthy balance of intestinal bacteria and gut health, respectively [1, 2]. Numerous in vitro and animal studies have been performed to demonstrate their safety [1, 2, 3, 4, 5] These two strains have been widely used alone as probiotic components in food supplements, thanks to their beneficial effects on human health. Bifidobacteria produce acetate and lactate as well as vitamins, antioxidants, polyphenols, and conjugated linoleic acids, whereas lactobacilli produce lactate and small proteins [10, 11, 12, 13] These bioactive metabolites produced by bifidobacteria and lactobacilli could act as a chemical barrier against pathogen proliferation, contributing to maintaining a correct balance between the microbial populations belonging to the phyla (Actinobacteria, Proteobacteria, Bacteroidetes and Firmicutes) normally distributed in the healthy adult human gut [11, 14]. Probiotic bacteria could represent an important strategy to antagonize nosocomial uro- and entero-pathogens, in the era of antibiotic and antimycotic resistance [9, 15, 16, 17, 18, 19, 20, 21, 22, 23]

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