Modulation of nonspecific mechanisms of defense by lactic acid bacteria: Effective dose

The purpose of this study was to determine the effect of a fermented milk p roduct containing Lactobacillus johnsonii La1 (formerly known as Lactobacil lus acidophilus La1) on the phagocytic activity of peripheral blood leukocy tes in healthy adult volunteers. Furthermore, we sought to define the effec tive doses of the bacteria, examine the effect on respiratory burst activit y, and, finally, examine the contribution made by the starter culture to th e biological effects. Volunteers were randomly distributed among three grou ps; each subject received one pot (150 ml) of fermented milk each day for 3 wk. The first two groups received a freshly prepared product fermented by Streptococcus thermophilus (group A) alone Or S. thermophilus and 10(7) cfu /ml L. johnsonii La1 (group B). Group C received a product stored for a per iod of 21 to 28 d and that contained S. thermophilus and 10(6) cfu/ml of L. johnsonii La1. Ingestion of L. johnsonii La1 did not significantly increase fecal lactobac illi counts. However, L. johnsonii La1 was able to survive intestinal trans it and was only recovered from the feces of the volunteers of groups B and C. The fermented base alone showed a weak effect on respiratory burst but n ot on phagocytic activity. However, the product containing 10(7) cfu/ml L. johnsonii La1 significantly enhanced both functions. The product containing 10(6) cfu/ml of L. johnsonii La1 had no significant effect on either funct ion. These results suggest that fecal persistence may not necessarily refle ct in vivo colonization and may not be a prerequisite for all forms of immu ne reactivity.