Objective　We assessed safety and efficacy of heat-killed Enterococcus faecalis strain EC-12（EC-12）regarding the molarity concentrations of organic acids in intestinal microflora in a randomized placebo controlled double-blind paralleled study.
Methods　A total of 48 Sub-optimal healthy Japanese adult women, 21-68 years old, were agreed to participate the study. 34 subjects were selected and 14 subjects were interviewed and excluded by a physician because of no Bifidobacterium levels. Subjects were randomly assigned to two groups（an EC-12 group and a placebo group）. They consumed a capsule either 200 mg EC-12 or 200 mg dextrin in daily for 4 weeks. Intestinal microflora was assessed using terminal restriction fragment length polymorphism（T-RFLP）analysis at baseline and 4 weeks after ingestion of EC-12 or placebo capsule. Fecal organic acids were also measured.
Results　A total of 25 subjects（EC-12 group, n＝12; placebo group, n＝13）completed the study. The primary endpoint of Bifidobacterium levels was significantly increased in the EC-12 group from the baseline to at 4 week after ingestion（P＝0.002）. Secondary endpoints of butyric acid and, propionic acid were also significantly increased in the EC-12 group（ P＝ 0.027, P＝0.009, respectively）. There are no adverse events, and safety parameters were no difference between two groups.
Conclusion　These results indicate that EC-12 was able to increase Bifidobacterium levels and fecal organic acids. In addition, the EC-12 are safe to ingest.