A number of bacterial species are found in high abundance in the faeces of healthy breast-fed infants, an occurrence that is understood to be, at least in part, due to the ability of these bacteria to metabolize human milk oligosaccharides (HMOs). HMOs are the third most abundant component of human milk after lactose and lipids, and represent complex sugars which possess unique structural diversity and are resistant to infant gastrointestinal digestion. Thus, these sugars reach the infant distal intestine intact, thereby serving as a fermentable substrate for specific intestinal microbes, including Firmicutes, Proteobacteria, and especially infant-associated Bifidobacterium spp. which help to shape the infant gut microbiome. Bacteria utilising HMOs are equipped with genes associated with their degradation and a number of carbohydrate-active enzymes known as glycoside hydrolase enzymes have been identified in the infant gut, which supports this hypothesis. The resulting degraded HMOs can also be used as growth substrates for other infant gut bacteria present in a microbe-microbe interaction known as ‘cross-feeding’. This review describes the current knowledge on HMO metabolism by particular infant gut-associated bacteria, many of which are currently used as commercial probiotics, including the distinct strategies employed by individual species for HMO utilisation.

中文翻译：

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婴儿肠道相关细菌利用母乳寡糖的分子策略

在健康母乳喂养的婴儿的粪便中发现了大量的细菌种类，据了解，这种现象至少部分是由于这些细菌代谢母乳寡糖 (HMO) 的能力所致。HMO 是母乳中仅次于乳糖和脂质的第三大丰富成分，是具有独特结构多样性且能抵抗婴儿胃肠道消化的复合糖。因此，这些糖完整地到达婴儿远端肠道，从而充当特定肠道微生物的可发酵底物，包括厚壁菌门、变形菌门，尤其是婴儿相关的双歧杆菌属。有助于塑造婴儿肠道微生物组。利用 HMO 的细菌配备了与其降解相关的基因，并且在婴儿肠道中发现了许多被称为糖苷水解酶的碳水化合物活性酶，这支持了这一假设。由此产生的降解 HMO 还可用作其他婴儿肠道细菌的生长底物，这些细菌存在于称为“交叉喂养”的微生物-微生物相互作用中。这篇综述描述了特定婴儿肠道相关细菌对 HMO 代谢的最新了解，其中许多细菌目前被用作商业益生菌，包括各个物种利用 HMO 所采用的独特策略。