Table 1.

Factors influencing the composition of breast milk and/or neonatal intestinal microbiota and some of proposed mechanisms and exerted effects.

Maternal factors	Effects on BM and/or neonatal gut microbiota
Genetics (1, 16, 26, 27)	Secretor status Se+ (associated with high presence of Bifidobacteria spp. in neonatal stools) and non secretor status Se− (higher percentage of Streptococcus spp.), Lewis gene; ethnicity; other factors not completely known.
Lactation phase (54, 57–59, 63)	Modulation of BM metabolites and microbial community, directly influencing neonatal gut microbiota and metabolic network
Breast milk composition (such as oligosaccharides, lipids) (10, 37, 38, 72)	Modulation of BM metabolites and microbial community, directly influencing neonatal gut microbiota and metabolic network. HMOs influence B. Fragilis, E. coli etc… HMOs and FAs influence Bifidobacteria spp. and Staphylococci spp. in neonatal gut
Body mass index (5, 82, 83)	Influence on maternal metabolic status
Diet, lifestyle and habits (2, 5, 17, 67, 82)	Influence played by ingested foods, maternal diseases or metabolic status
Delivery route (vaginal, elective or emergency cesarean section) (5, 72, 82–85)	Induce neonatal colonization with maternal vaginal microbiota during spontaneous delivery. S. Salivarius detected only in BM samples from mothers undergone cesarean section. Other factors not completely known
Gestational age at delivery (86)	Modulation of BM metabolites and microbial community, directly influencing neonatal gut microbiota and metabolic network
Administration of antibiotics (17, 33)	Influence on maternal intestinal microbiota
Dysbiosis and/or mastitis (2, 17, 73, 74)	Neonatal contact with potentially dangerous microbial communities