Lactulose Differently Modulates the Composition of Luminal and Mucosal Microbiota in C57BL/6J Mice

In this study, C57BL/6J mice were fed diets supplemented with different proportions of lactulose (0%, 5%, and 15%) for 2 weeks to study its effects on the luminal and mucosal microbiota. The luminal and mucosal samples of cecum and colon were investigated. After high-lactulose treatment (15%), pH of the luminal contents decreased from 6.90-7.72 to 5.95-6.21 from the cecum to distal colon, and the amount of total short-chain fatty acids in the cecum was significantly increased. The luminal content was mostly dominated by Firmicutes, Actinobacteria, and Bacteroidetes, while the mucus was dominated by Firmicutes, Proteobacteria, and Bacteroidetes. The abundance of Actinobacteria was significantly increased in the content, and Proteobacteria was the most abundant phylum (∼50%) in the mucus after high-lactulose treatment. At the genus level, Bifidobacterium and Akkermansia were both significantly increased in the content, and Helicobacter was the most abundant in the mucus.