Commentary: Relationship between Milk Microbiota, Bacterial Load, Macronutrients, and Human Cells during Lactation

The recent contribution by Boix-Amorós et al. (2016) reveals certain associations among the microbiota, bioactive components and nutrients found in human colostrum and breast milk of 21 healthy Spanish lactating mothers. We would like to emphasize the importance of their findings, discuss some phenomena and highlight the relevant future research directions (Figure 1). The commensal microbiota, as part of epigenetic landscape, reflects human health status by its diversity, composition and metabolic activity (Moya and Ferrer, 2016). An improved understanding of the factors controlling health associated bacterial interactions may, upon perturbation, define novel therapeutic or preventive measures to restore individual's dynamic microbial equilibria and immune homeostasis (Peterson et al., 2015). Probiotics were demonstrated as an effective tool in lactational mastitis interventions (Arroyo et al., 2010), and may even hold potential in breast cancer prevention (Chan et al., 2016; Urbaniak et al., 2016). In the study by Boix-Amorós et al. (2016), microbial communities, again, were confirmed as complex and individual-specific. High inter-subject variability was disclosed for the composition and the number of bacteria per ml, while higher total bacterial load was not associated with lower diversity of milk sample. Namely, as reported previously, the milk microbiome of mastitis-affected women suffered a loss of bacterial diversity, while an increase in sequences related to the presumptive etiological agents was also observed (Jiménez et al., 2015). Staphylococci and streptococci were classified in dominant core of genera, existing at all three lactation sampling points (Boix-Amorós et al., 2016). The study further suggested that the specific microbiota composition, rather than total sample bacterial load, might trigger the mammary gland immune responses. Moreover, the positive correlation was only established between the staphylococci proportion and somatic cell count (SCC). Specifically, the SCC biomarker was earlier reported (Hunt et al., 2013) to be roughly 10-fold increased in milk from mastitic compared to milk from healthy breasts. Similarly to the work by Boix-Amorós et al. (2016), our recent publication studied the colostrum bioactive potential of 45 healthy Slovenian mothers (Obermajer et al., 2015) and qPCR approach was applied on the automatedly extracted colostrum microbial DNA. The interactions among target bacterial groups were investigated. As in previous reports concerning