Human Milk Microbiota: Origin and Potential Uses.

At the beginning of the 21st century, some pioneer studies provided evidence of the existence of a site-specific human milk microbiota. Hygienically collected milk samples from healthy women contain a relatively low bacterial load, which consist mostly of Staphylococcus, Streptococcus, lactic acid bacteria, and other gram-positive bacteria (Corynebacterium, Propionibacterium, and Bifidobacterium). DNA from strict anaerobic bacteria is also detected in human milk samples. The origin of human milk bacteria still remains largely unknown. Although the infant's oral cavity and maternal skin may provide microbes to milk, selected bacteria of the maternal digestive microbiota may access the mammary glands through oral- and enteromammary pathways involving interactions with immune cells. In addition, when milk is collected using external devices, such as breast pumps, some microorganisms may arise from unhygienic handling as well as from the water used to clean and rinse the devices, for example. The human milk microbiota has a wide spectrum of potential uses. Most of them have been focused on the infant (including the preterm ones), but some bacterial strains present in human milk have also a big potential to be used to improve the mother's health, mainly through the prevention or treatment of infectious mastitis during lactation.