Isolation of lactate-utilizing butyrate-producing bacteria from human feces and in vivo administration of Anaerostipes caccae strain L2 and galacto-oligosaccharides in a rat model

Lactate-utilizing butyrate-producers were isolated from human feces and identified based on the sequences of 16S rRNA gene. Anaerostipes caccae strain L2, one of the seven human fecal isolates, was administered to rats with galacto-oligosaccharides (GOS) as bifidogenic carbohydrates for stimulating lactate formation in the hindgut. Ingestion of GOS alone increased concentrations of cecal lactate and butyrate compared with control rats (P<0.05). Additional administration of strain L2 on GOS tended to enhance the promoting effect of GOS on cecal butyrate formation (P=0.06) and lowered the mean value of cecal lactate concentration (P=0.32). Consequently, cecal and fecal butyrate concentrations in rats administered with both strain L2 and GOS were significantly higher than those in the control rats (P<0.01 and P<0.05, respectively). Significant changes were observed in the other fermentation acids, such as succinate, acetate, and propionate, depending on the ingestion of strain L2. Administered strain L2 was retrieved from the cecal content of a rat based on randomly amplified polymorphic DNA analysis. The results suggest that synbiotic ingestion of lactate-utilizing butyrate-producers and GOS alters the microbial fermentation and promotes the formation of beneficial fermentation acids, including butyrate, in the gut.