The effect of consumption of milk fermented by Lactobacillus casei strain Shirota on the intestinal microflora and immune parameters in humans

Objective: To determine the effect of consumption of milk fermented by Lact obacillus casei strain Shirota (L. casei Shirota) on the composition and me tabolic activities of the intestinal microflora, and immune parameters in h umans. Subjects: Twenty healthy male subjects aged 40-65 years were selected. Design: A placebo-controlled trial was performed in which 10 subjects were randomly assigned to a control and 10 to a treatment group. During the firs t and last two weeks of the 8-week study the subjects received a strictly c ontrolled diet without fermented products. The same controlled diet was giv en during the intermediate 4-week test period but then the treatment group received three times daily 100 mi of fermented milk containing 10(9) CFU L. casei Shirota/ml, whereas the same amount of unfermented milk was given to the subjects in the control group. Results: In comparison to the control group, the consumption oft. casei Shi rota-fermented milk resulted in an increase of the Lactobacillus count in t he faeces in which the administered L. casei Shirota was predominant at the level of 10(7) CFU/g wet faeces. This was associated with a significant in crease in Bifidobacterium counts (P < 0.05). Some shifts in the other bacte rial species were found, such as a decreased number of Clostridium; however the differences were not statistically different between the treatment and the control groups. The beta-glucuronidase and beta-glucosidase activities per 10(10) bacteria decreased significantly (P < 0.05) at the second week of the 4-week test pe riod with the consumption of L. casei Shirota-fermented milk. Furthermore, the consumption of the fermented milk product resulted in a slight but sign ificant increase in the moisture content of the faecal samples (P < 0.05). No treatment effects were observed for any of the immune parameters measure d (including natural killer (NK) cell activity, phagocytosis and cytokine p roduction). Conclusions: The results suggest that consumption of L. casei Shirota-ferme nted milk is able to modulate the composition and metabolic activity of the intestinal flora and indicate that L. casei Shirota-fermented milk does no t influence the immune system of healthy immunocompetent males.