A randomized clinical trial of the effect of yoghurt on the human salivarymicroflora

Yoghurt is active against some human pathogens, so this experiment tested w hether it is also active against the salivary microflora. A clinical trial was designed, with volunteers aged between 23 and 37 years. Initially, for 8 weeks, they consumed neither yoghurt nor casein-free soybean ice cream (p hase 1). They were then split randomly into test (yoghurt) and control (ice cream) groups and required to consume 125 g of these foods twice daily for 8 weeks (phase 2) and then to avoid them for the following 2 weeks (phase 3). Many potential sources of microbial fluctuation were standardized. Sali vary samples were then collected at regular intervals of 2 weeks. For each group and phase, the mean logarithms of the salivary counts for total viabl e flora, oral streptococci, mutans streptococci, lactobacilli and Candida w ere calculated. The prevalence of Streptococcus thermophilus and Lactobacil lus bulgaricus was also assessed. Twenty test and 22 control participants c ompleted the study. At phase 2, the mean for mutans streptococci was lower in the test than in the control group (3.6 vs. 4.0 log colony-forming units /ml; P = 0.02). Moreover, the mean had decreased in all test participants w ith high phase 1 means for lactobacilli as compared to only 36.4% of those with low phase 1 means (P = 0.01). L. bulgaricus was transiently detected i n three test participants during phase 2. These results suggest that yoghur t does have some activity against the salivary microflora, but this does no t seem to be due to the installation of yoghurt microorganisms in the mouth . (C) 2001 Elsevier Science Ltd. All rights reserved.