Survival of lactococci during passage through mouse digestive tract

One of the important properties of probiotics is the ability to survive in the intestine. There have been few studies on the probiotic property of lactococci, since they are formally not considered to be natural inhabitants of the intestine. To evaluate lactococci as probiotic bacteria, we investigated their ability to survive during gastric transit by in vitro and in vivo tests. When exposed to an in vitro simulated gastrointestinal environment, such as low pH and bile, only Lactococcus lactis subsp. lactis bv. diacetylactis N7 showed a moderate survival rate among the four strains tested. The tested strains were orally administered to mice, and intestinal passage of the ingested strains was monitored by two methods: antibiotics and PCR. Viable cells of strain N7 were recovered from feces within 24-48 h after administration but not at 72 h. Lactococcus lactis subsp. cremoris ATCC 19257, which had a poor survival rate in vitro test, was also detected at 12 h but not at 24 h. These results indicate that lactococci can reach the mouse intestine alive, but not colonize it. If administered daily, viable strain N7 may exist continuously in the intestine. The effect of strain N7 on intestinal microbial balance and on animal health will be the subject of a further study.