Survival through the gut is considered a key characteristic of probiotic strains as the mechanism of activity is associated with the transient presence, growth and activity of the live probiotic cells in the gut. The strongest evidence for survival is detection of the strain in the faeces of people after they have consumed the probiotic.
Lactobacillus casei Shirota, the strain in Yakult, was selected and cultivated because of its ability to survive the harsh conditions of the gut. There are several peer-reviewed publications that describe human studies showing the survival of L. casei Shirota including, but not limited to, studies in European (Tuohy et al. 2007) and Asian populations (Mai et al. 2017), children (Wang et al. 2015) and critically ill children (Srinivasan et al. 2006).
In vitro or model studies are not proof of gut survival in vivo, however they do provide useful information on factors that can affect the viability of the strain. When L. casei Shirota was exposed to physiological levels of gastric, bile, and pancreatic juices, for a realistic time of digestion, it was confirmed to have an excellent survivability, particularly when embedded in a milk matrix (Lo Curto et al. 2011).
Probiotic bacteria consumed are generally only transient in the intestinal tract and cannot establish permanent residency in the gut of the host. Within weeks of ceasing probiotic intake, generally the strains consumed are no longer detected in the faeces. However, studies suggest that complementary probiotic intake may help our resident microbes by encouraging the growth and numbers of our own bacteria; see our page of MODULATION to find out how Lactobacillus casei Shirota modulates the gut microbiota.
Survival of Lactobacillus casei Shirota through the gut
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.
Lo Curto et al. (2011) Survival of probiotic lactobacilli in the upper gastrointestinal tract using an in vitro gastric model of digestion. Food Microbiology 28:1359-1366
Mai et al. (2017) Recovery of Lactobacillus casei strain Shirota (LcS) from the intestine of healthy Vietnamese adults after intake of fermented milk. Asia Pacific Journal of Clinical Nutrition 26(1):72-77.
Srinivasan et al. (2006) Clinical safety of Lactobacillus casei Shirota as a probiotic in critically ill children. Journal Pediatric Gastroenterology and Nutrition 42:171-173.
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.