Figure 1.

Origins of milk microbiota revisited. Two pathways for the origins of milk microbiota have been hypothesized: the entero-mammary pathway and retrograde translocation.¹⁰ We propose that translocation also occurs from the maternal oral cavity (oro-mammary pathway). Further, our study suggests that direct breastfeeding at the breast vs. pump expression could influence the milk microbiota composition⁶ potentially indicating the pump apparatus as an additional source of retrograde inoculation and/or contamination of the expressed milk. Resident breast microbiota could be another source of mammary gland colonization. Depending on the origin of the bacteria, different factors could be associated with the composition of the milk microbiota.