Isolation and identification of milk oligosaccharide–degrading bacteria from the intestinal contents of suckling rats

抄録

We report the isolation of bacteria capable of degrading milk oligosaccharides from suckling infant rats. The bacteria were successfully isolated via a selective enrichment method, in which the serially diluted intestinal contents of infant rats were individually incubated in an enrichment medium containing 3′-sialyllactose (3′-SL), followed by the isolation of candidate strains from streaked agar plates and selection of 3′-SL–degrading strains using thin-layer chromatography. Subsequent genomic and phenotypic analyses identified all strains as Enterococcus gallinarum. The strains were capable of degrading both 3′-SL and 6′-SL, which was not observed with the type strain of E. gallinarum used as a reference. Furthermore, a time-course study combining high-performance anion-exchange chromatography with pulsed amperometric detection revealed that the representative strain AH4 degraded 3′-SL completely to yield an equimolar amount of lactose and an approximately one-fourth equimolar amount of sialic acid after 24 hr of anaerobic incubation. These findings point to a possibility that the enterococci degrade rat milk oligosaccharides to “cross-feed” their degradants to other members of concomitant bacteria in the gut of the infant rat.