# 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
#### 4.3.3 Evidence on Gut Transmission to Breast Milk  
Recently, several reports have shown that orally administrated probiotictic microorganisms to pregnant women could also be traced in the breast milk or in the infants' stool (Table 1). These studies have proven the homogeneity of bacterial strains with more precise molecular techniques [48; 110; 111; 112]. [PERSON] et al. utilized culture-based techniques and demonstrated that 12% of women in their probiotic group had viable _L. reuteri_ strains in their colostrum samples compared with 2% in the placebo group [111]. Similarly, [PERSON] et al. reported the presence of _L. fermentum_ CECT5716 and _L. salivarius_ CECT5713 in the milk of mothers who had undergone probiotic treatment for mastitis after 21 days of supplementation [112]. In another small trial, four of 10 women had viable cultures of _L. rhamnus_ strain LC705 isolated from breast milk samples after supplementation with _L. rhamnus_ strain LC705 [113]. Additionally, the results of subsequent trials also  
Figure 4: Entero-mammary pathway showing the movement of gut microbial groups into the mammary glands.  
suggested that maternal supplementation with _L. fermentum_ CECT5716 may increase levels of microbial population in the breast milk samples compared to the control and under antibiotic treatments [48].  
The orally administrated bacterial strains detected in breast milk such as _L. fermentum_ CECT5716, _L. salivarius_ CECT5713 [112], or _L. rhamns_ strain LC705 [113] were initially isolated from breast milk samples. This could imply the presence of selective sampling and translocation of these bacteria, which have a natural affinity toward breast milk origin bacteria. In this context, translocated bacteria might have specific induction mechanisms to activate DCs [39]. Therefore, the natural gastrointestinal microorganisms or artificially administered probiotic strains are selectively translocated from the maternal gut into mammary glands through the entero-mammary pathway. Because of the small number of mother-infant pairs studied, the biological validity of such results is limited.  
GALT lymphoid cells migrate to the mammary gland in humans and rodents, establishing an entero-mammary bond and leading to the so-called \"normal mucosal mechanism,\" in which immune cells migrate between distant mucosal sites. In contrast to these observations, cattle studies have shown that lymphoid cell movement between the gut and the mammary gland is limited, suggesting that the entero-mammary relationship in ruminants is less functional [10]. While most mononuclear phagocytes in breast milk are produced from peripheral blood monocytes, it has recently been hypothesized that a proportion of these mononuclear phagocytes are dendritic cell-like cells that originate in GALT. These cells collect luminal microbiota, and then transport these microbial components to the mammary gland. This pathway teaches the neonatal immune system to recognize commensal-associated bacterial molecular patterns and to react properly to them [19; 83].