Breast, Milk and Microbes: A Complex Relationship that Does Not End with Lactation

Abstract

Until relatively recently, the extent of microbiota presence in the human breast was under-appreciated. A high-throughput sequencing study and culture-based studies have demonstrated the extensive presence of microbes in human milk, with their origin believed to be from the skin, oral cavity and via gut translocation. Since formula milk substitutes do not contain these bacteria, what benefits are denied to these infants? The addition of probiotic bacteria to some infant formula is meant to provide some benefits, but these only contain one species and the dose is relatively high compared with breast milk. Many questions of importance to women's health arise from these findings. When, how and what types of microbes colonize the breast at different stages of a woman's life, including postlactation, and what effect do they have on the host in the short and long term? This article discusses some aspects of these questions.

Microbiota of Human Breast Tissue

“…We first suggested the potential for a breast microbiome in 2012 (10), and this has now been confirmed in the present study, and recently by Xuan et al (30), who examined breast tumor and normal adjacent tissue also by using next-generation sequencing techniques. In our study, none of the 81 women recruited had any clinical signs or symptoms of breast infection, yet bacteria were still detected in all Canadian samples, which were analyzed by both culture and molecular techniques, and Irish samples, which were analyzed just by molecular techniques.…”

“…These studies have been made possible with the use of deep-sequencing technologies, and sites once thought of as sterile, such as the stomach, bladder, and lungs, have now been shown to harbor an indigenous microbiota (7)(8)(9). We hypothesized that microbes may also be present in breast tissue given the known presence of bacteria in human milk (10). This is not surprising considering that skin and oral bacteria have access to the mammary ducts through the nipple (11), with some recent studies suggesting their source to be from the mother's gastrointestinal tract (12).…”

The Completed Self: An Immunological View of the Human-Microbiome Superorganism and Risk of Chronic Diseases

“…Additionally, breast milk is an important source of gut microbiota for the infant. Urbaniak et al [43] indicate that breast milk provides the infant with a significant amount and diversity of microbes that are lacking in formulas. Even probiotic supplemented formulas lack the diversity of bacteria that is provided to the infant via breast milk [43].…”

The Gut Microbiota and Inflammation in Rheumatoid Arthritis

“…Breast milk composition is another proven shaping factor of individuals' microbiota proile (Biidobacterium is among the dominant gut microbiota in breast-fed infants compared to artiicially fed ones and is deicient in patients with RA). Aging; lifestyle paterns including diet, smoking, and obesity; and infections also contribute [31][32][33][34].…”