Phage diversity in human breast milk: a systematic review.

Breast milk is not sterile. The microbiome in human milk serves as a crucial source of early gut microbes for infants, directly impacting the host's health. This microbiome includes bacteria, viruses, archaea, and fungi. Bacteriophages, as key components of the virome, continually prey on bacterial hosts, thereby influencing the development of early gut microbial communities. Pertinent records from various databases, including EMBASE, Cochrane Library, PubMed, and Web of Science, were comprehensively reviewed against inclusion criteria up to March 24, 2025. A checklist was employed to assess the risk of bias in the selected studies. After screening a total of 635 records, we included 5 studies with 182 women and 251 samples. Seven families of bacteriophages were identified, primarily Herelleviridae, Myoviridae, Podoviridae, Siphoviridae, Caudoviridales, Microviridae, and Inoviridae. Their abundance varies at different stages of lactation and can be vertically transmitted through breastfeeding. However, due to the limited number of studies and methodological differences, it is not yet possible to determine which maternal and infant characteristics influence the abundance of these bacteriophages.

conclusionHuman milk contains abundant bacteriophages that bind to specific bacterial hosts and are transmitted vertically from mother to infant, collectively shaping the infant's gut microbiome. Conducting more longitudinal studies on mother-infant pairs will help better determine the composition of bacteriophages in human milk and their functional impact on infant development. WHAT IS KNOWN: • Human milk is a source of diverse microbes, including bacteriophages, that contribute to the establishment of the infant gut microbiome. • Bacteriophages can influence bacterial populations by infecting specific bacterial hosts. WHAT IS NEW: • Human milk harbors abundant and diverse bacteriophages that are vertically transmitted from mother to infant. • Current evidence underscores the need for longitudinal studies to clarify the role of milk-derived bacteriophages in shaping infant gut microbiota and development.