Prebiotic effects of oligosaccharides on selected vaginal lactobacilli and pathogenic microorganisms

The purpose of this study was to select endogenous human vaginal lactobacilli strains on the basis of the main probiotic properties observed in the vaginal environment in order to use them for the evaluation of the potential prebiotic properties of oligosaccharides. From vaginal samples of 50 women with a normal flora, 17 lactobacilli strains were first isolated because of their high level of hydrogen peroxide production. Then six strains were selected mainly for their ability (i) to adhere to vaginal cells, (ii) to produce compounds in sufficient amount, such as lactic acid, having an inhibitory action on pathogens, and less importantly, (iii) to demonstrate arginine deiminase activity. These six strains were found to belong to three distinct species: Lactobacillus crispatus, L. jensenii and L. vaginalis. One strain of each species was chosen as a potential vaginal probiotic strain with regard to our criteria. These three strains were then used to evaluate the prebiotic properties of different oligosaccharide series: two fructooligosaccharide series (FOS Actilight and FOS Raftilose) and two glucooligosaccharide series varying by their osidic linkages (alpha-1,6/alpha-1,4 GOS and alpha-1,2/alpha-1,6/alpha-1,4 GOS). The test was based on the ability of the oligosaccharides to promote the growth of the three beneficial strains selected but not of pathogenic microorganisms often encountered in urogenital infections such as Candida albicans, Escherichia coli and Gardnerella vaginalis. Oligosaccharide hydrolysis was followed by HPLC analysis. This revealed that two oligosaccharide series (FOS Actilight DP3 and all alpha-1,6/alpha-1,4 GOS DP > or = 4) were used only by the lactobacilli strains, the pathogenic microorganisms being unable to metabolise them. The selected lactobacilli and oligosaccharides are good candidates for incorporation in a formula to prevent vaginal infections.