# An Insight into Probiotics Bio-Route: Translocation from the Mother's Gut to the Mammary Gland
## 4 Microbial Transmission: Solving the Labyrinth Path
### Cross-Contamination from Infants' Oral Cavity
The changes in gut microbial population over time plays a critical role in normal pregnancy in promoting weight gain, raising maternal metabolic adaptations, and supporting the growth of the fetus [9; 81; 83]. Even after birth, the maternal microbiota does not appear to return to its previous state [83]. As the postpartum period is linked to significant hormonal shifts, it was expected that it could reveal more interesting facts of the hormonal effect on the maternal gut microbiome [9]. Despite the microbial transition before or after postpartum periods, it is an immensely popular fact that maternal gut has a great influence on the breast milk microbiota. [PERSON] et al. performed the earliest comparison on the origin of milk microbiota using random amplification of the polymorphic DNA (RAPD) technique [37]. The RAPD profiles of lactic acid bacteria isolates from breast milk were compared with other isolates collected from various body sites. The study explained that none of the lactic acid bacteria isolates from the breast milk were identical to those from the breast areolar skin surface [37; 84]. This is also supported by the research done by [PERSON] et al. [42]. The study reported that the presence of skin microflora in the HBM samples seems to be widespread. However, the presence of _Lactobacillus_ and _Bifidobacterium_ must originate from the maternal gastrointestinal environment [42]. [PERSON] et al. conducted a study for a large number of isolates by using RAPD and matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) analyses [85]. The researchers found that the RAPD genotypes of _L. plantarum_, _L. fermentum_, _L. brevis_, _Enterococcus facetlis_, _Enterococcus faecalis_, and _P. pentosaceus_ recovered from breast milk, mothers' guts, and infants' feces were identical [85]. [PERSON] et al. utilized the pyrosequencing technique to reveal vertical sharing of microbiota between maternal gut, breast milk and infant's gut [33]. Despite the predominance of skin microflora, the study also found that gastrointestinal anaerobic bacteria including _Bacteroides_, _Bifidobacterium_, _Blautia_, _Clostridium_, _Collinsella_, _Panobacteroides_, _Veillonella_, and facultative _Lactobacillus_ spp. were detected in all three ecosystems analyzed. [PERSON] et al. reported that _Bacteroides_ and _Bifidobacterium_ strains had the highest potential for vertical transfer from maternal gut into her breast milk samples [33]. The above-mentioned studies assist the statement that the -internal gut bacteria reach the breast milk and colonize the gut of the breast-fed neonate through entero-mammary pathway trafficking [17; 86]. However, only certain gut species have been identified from breast milk. Sampling and selective transfer of a specific strain or composition of maternal gut microbiota into the mammary glands remain to be completely explored. [PERSON] et al. performed metagenomics investigation to highlight the transmission of probiotic Bifidobacterium communities as they are important representatives in the intestinal microbiota of infants [86]. With Bifidobacterium-rial ITS profiling coupled with shotgun metagenomics analyses performed in the study, a common Bifidobacterial profile was identified to be similar among the mother-infant pairs. The targeted genome reconstruction from the microbiome also confirmed that these specific Bifidobacterial strains were persistent in the infant gut for six months after birth [69; 86]. Later, the same group revealed that Bifidobacterial communities are widely spread among mammalian groups that include domesticated animals such as dogs, cats, cows, sheep, goats, horses, and pigs as well as 46 other non-primate mammals including humans and 13 non-human primates [8]. The study reported that the Bifidobacterial strains were found to be transferred from the mother through breast milk. These findings support the hypothesis that probiotics bacteria found in HBM, especially Bifidobacterial strains, are directly acquired from the maternal gut.