Breastfeeding is associated with considerable health benefits for infants. Aside from essential nutrients, immune cells and bioactive components, breast milk also contains a diverse range of microbes, which are important for maintaining mammary and infant health. In this review, we summarise studies that have investigated the composition of the breast milk microbiota and factors that might influence it.

We identified 44 studies investigating 3105 breast milk samples from 2655 women. Several studies reported that the bacterial diversity is higher in breast milk than infant or maternal faeces. The maximum number of each bacterial taxonomic level detected per study was 58 phyla, 133 classes, 263 orders, 596 families, 590 genera, 1300 species and 3563 operational taxonomic units. Furthermore, fungal, archaeal, eukaryotic and viral DNA was also detected. The most frequently found genera were Staphylococcus, Streptococcus Lactobacillus, Pseudomonas, Bifidobacterium, Corynebacterium, Enterococcus, Acinetobacter, Rothia, Cutibacterium, Veillonella and Bacteroides. There was some evidence that gestational age, delivery mode, biological sex, parity, intrapartum antibiotics, lactation stage, diet, BMI, composition of breast milk, HIV infection, geographic location and collection/feeding method influence the composition of the breast milk microbiota. However, many studies were small and findings sometimes contradictory. Manipulating the microbiota by adding probiotics to breast milk or artificial milk offers an exciting avenue for future interventions to improve infant health.

母乳喂养对婴儿具有相当大的健康益处。除了必需的营养素，免疫细胞和生物活性成分外，母乳还包含多种微生物，这些微生物对于维持乳腺和婴儿健康非常重要。在这篇综述中，我们总结了研究母乳菌群的组成以及可能影响母乳菌群的因素的研究。

我们确定了44项研究，调查了2655名女性的3105例母乳样本。几项研究报告说，母乳中的细菌多样性高于婴儿或产妇的粪便。每个研究中检测到的每种细菌分类标准的最大数量为58个门，133个类别，263个订单，596个科，590个属，1300个物种和3563个操作分类单位。此外，还检测到真菌，古细菌，真核和病毒DNA。最常发现的属是葡萄球菌，链球菌乳杆菌，假单胞菌，双歧杆菌，棒状杆菌，肠球菌，不动杆菌属，Rothia，Cutibacterium，Veillonella和拟杆菌。有证据表明，胎龄，分娩方式，生物学性别，胎次，产时抗生素，哺乳期，饮食，BMI，母乳组成，HIV感染，地理位置和收集/喂养方法会影响母乳微生物群的组成。但是，许多研究规模很小，发现有时是矛盾的。通过在母乳或人造乳中添加益生菌来控制微生物群，为将来改善婴儿健康的干预措施提供了令人兴奋的途径。