# An Insight into Probiotics Bio-Route: Translocation from the Mother's Gut to the Mammary Gland
## 3 Microbial Partners of Human Milk 'Factory'
### Predicting the Core of Human Milk Microbiota  
Human milk core microbiota have been estimated by culture-independent techniques [21; 27; 30]. [PERSON] et al. reported that the core of human milk microbiota consisted of nine bacterial genera. Based on the pyrosequencing technique, various reports have indicated the presence of _Streptococcus_, _Staphylococcus_, _Serratia_, and _Corynebacteria_ as the most abundant genera in human milk, besides _Pseudomonas_, _Ralstonia_, _Propioniibacterium_, _Sphingomonas_, and _Bradyrhizobenzene_[30]. In contrast, [PERSON] et al. used metagenomics analysis on the milk samples from healthy mothers. Early reports suggest a microbial core composed of seven genera including _Staphylococcus_, _Streptococcus_, _Bacteroides_, _Faecalibacterium_, _Ruminococcus_, _Lactobacillus_, and _Propioniibacterium_[15]. Recently, [PERSON] et al. reported a microbial core of 10 bacterial groups that were abundantly found at each time point throughout six months of postpartum. _Streptococcus_, _Staphylococcus_, and _Propioniibacterium_ were found in all samples, whereas _Pseudomonas_, _Veillonella_, _Pililbacter_, _Gemella_, _Bacteroides_, _Preotella_, and _Corynebacterium_ were found in more than 90% of samples [66]. Meanwhile, [PERSON] et al. [20] reported a core microbiota consisting of 12 genera including _Pseudomonas_, _Staphylococcus_, _Streptococcus_, _Elizabethkingia_, _Variovorax_, _Bifidobacterium_, _Flavobacterium_, _Lactobacillus_, _Stentroroplomonas_, _Brewundomonas_, _Chryseobacterium_, and _Enterobacter_. This study characterized the bacterial population in breast milk and infant stool collected over the first three months of life, among 10 mother-infant pairs [20]. Therefore, determination of core microbiota in human milk is not easy to standardize due to multiple factors such as geographic locations, milk collection and storage, or analytical methods. Despite these variabilities, the core human milk microbiota is mostly dominated by four bacteria phyla, which are _Firmicutes_ (such as _Staphylococcus_, _Clostridium_, _Lactobacillus_), _Actinobacteria_ (such as _Propioniibacterium_, _Corynebacterium_), _Proteobacteria_ (such as _Pseudomonas_, _Ralstonia_, _Sphingomonas_, _Bradyrhizobiacea_), and _Bacteroidetes_ (such as _Prevotella_) [14; 15; 21; 30; 66]. [PERSON] et al. suggest that this human milk microbial core might vary, but the reported additional genera in several studies are not consistently represented in all of the studies [14]. Furthermore, these milk microbial compositions are dynamic where it changes from highly diverse as lactation progresses [20; 36; 60]. Recently, it was confirmed that the microbial core in the human milk is not randomly distributed [60]. The microbial composition in the human milk might be due to specific localization. The study performed the first microbial network analysis in the breast milk samples using artificial neural networks (ANNs) to highlight the natural links among variables. Microbial networking enables a new understanding of the interactions existing within a bacterial ecosystem. Microbiome is dynamic and highly heterogeneous, where the role of each member is not often well-defined [67]. As a result, the bacterial network is proving to be a valuable method for deciphering microbial associations and assessing the effect of different interactions with the host. The study will identify the main \"hubs\", which is represented by the utmost significant member in a bacterial population [60; 67]. [PERSON] et al. reported that a streptococci variant, _Abiotropia_ spp., is an important hub in the microbial network found in colostrum and mature milk from Italian women [68]. This bacterial genus is a common oral cavity microorganism that can also be found in the genitourinary tract and gastrointestinal tract [69]. Thus, the researchers hypothesized that its existence in human milk could be attributed to direct entrance through the mammary ducts while breastfeeding [30] or the entero-mammary pathway [52].