A Postbiotic Consisting of Heat-Treated Lactobacilli Has a Bifidogenic Effect in Pure Culture and in Human Fermented Fecal Communities

The gut microbiota has a significant impact on host health. Dietary interventions using probiotics, prebiotics, and postbiotics have the potential to alter microbiota composition and function. Other therapeutic interventions, such as antibiotics and fecal microbiota transplantation, have also been shown to significantly alter the microbiota and its metabolites. Supplementation of a fecal fermentation model of the human gut with a postbiotic product, Lactobacillus LB, led to changes in microbiome composition (i.e., increase in beneficial bifidobacteria) and associated metabolic changes (i.e., increased acid production). Lactobacillus LB is a heat-treated preparation of cellular biomass and a fermentate generated by Limosilactobacillus fermentum CNCM MA65/4E-1b (formerly known as Lactobacillus fermentum CNCM MA65/4E-1b) and Lactobacillus delbrueckii subsp. delbrueckii CNCM MA65/4E-2z, medically relevant strains used to produce antidiarrheal preparations. In pure culture, Lactobacillus LB also stimulates the growth of a range of bifidobacterial species and strains. Lactobacillus LB-like preparations generated using other Lactobacillaceae, including commercially available probiotic bacteria, did not have the same impact on a model strain (Bifidobacterium longum subsp. infantis ATCC 15697). This bifidogenic activity is heat and enzyme stable and cannot be attributed to lactose, which is a major constituent of Lactobacillus LB. L. fermentum CNCM MA65/4E-1b is largely responsible for the observed activity, and there is a clear role for compounds smaller than 1 kDa. IMPORTANCE In general, disruptions to the gut microbiota are associated with multiple disorders in humans. The presence of high levels of Bifidobacterium spp. in the human gut is commonly considered beneficial. Bifidobacteria can be supplemented in the diet (as probiotics), or those bifidobacteria already present in the gut can be stimulated by the consumption of prebiotics such as inulin. We demonstrate that Lactobacillus LB (a product consisting of two heat-killed lactic acid bacteria and their metabolites) can stimulate the growth of bifidobacteria in human fermented fecal communities and in pure culture. Given the heat treatment applied during the production process, there is no risk of the lactic acid bacteria colonizing (or causing bacteremia in) vulnerable consumers (infants, the immunocompromised, etc.). Lactobacillus LB has the potential to affect human health by selectively promoting the growth of beneficial bacteria.