Several studies have shown that probiotic consumption not only increases the presence of the probiotic strain being consumed, but also modulates the resident gut microbiota by encouraging the growth and numbers of our own bacteria. The ability for Lactobacillus casei Shirota to modulate the gut microbiota has been reported in a number of peer-reviewed publications including intervention trials in children (Wang et al. 2015) and healthy adults (Tuohy et al. 2007).
Increase in lactobacilli and bifidobacteria in the gut of healthy adults
This double-blind, placebo-controlled study at the University of Reading, involved 20 healthy volunteers who consumed either L. casei Shirota (at least 13x109 CFU) as a fermented milk drink or placebo for 21 days. Stool samples were collected at days 0, 7, 14, 21 and 28 to measure survival of L. casei Shirota and changes to faecal bacteria.
Seven days after subjects started to take the probiotic, L. casei Shirota was recovered at a mean level of 1.1 x 107 CFU/g of faeces, and this level was maintained throughout the course of probiotic consumption and decreased after participants stopped consuming the probiotic.
Concurrently, in subjects consuming L. casei Shirota, an increase in total lactobacilli was observed, which persisted even after probiotic consumption had stopped. Bifidobacteria were also found to increase during the 21 days, but this increase was not sustained once consumption of L. casei Shirota had stopped (see Figure 1).
Figure 1. The population of Bifidobacterium and Lactobacillus in volunteers given the probiotic over the 28-day study.
Lactobacillus: Gram-positive facultative anaerobic rods found widely in nature, often used to make fermented foods such as cheese, yoghurt, pickles, salami etc. Considered part of the normal commensal intestinal microbiota; detected in adults at about 106 to 108 cells per gram of faeces (wet weight).
Bifidobacterium: Gram-positive anaerobes, often with a branched (bifurcated) appearance. Produce lactic acid but generally not considered ‘real’ lactic acid bacteria due to phylogenetic and metabolic differences. Early colonisers of the gut; breast feeding promotes this. Major constituents of the adult colonic microbiota, detected at about 108 to 1010 cells per gram of faeces (wet weight).
Tuohy et al. (2007) Survivability of a probiotic Lactobacillus casei in the gastrointestinal tract of healthy human volunteers and its impact on the faecal microflora. J Appl Microbiol 102(4):1026-1032.
Wang et al. (2015) Intestinal Microbiota Profiles of Healthy Pre-School and School-Age Children and Effects of Probiotic Supplementation. Annals Nutrition & Metabolism 67:257-266.