Microbiome of the normal breast

The microbiome of the human breast has been examined via 16S rRNA sequencing. Although the breast tumor microbiome has been previously investigated, the bacteria populating the healthy breast, lacking any disease-associated histological abnormality remains uncharted territory. Therefore, this project aimed to define the microbiota of the normal breast and its association with risk factors for breast cancer development. The study cohort included normal (N= 403), normal adjacent to tumor (NAT, N=61), tumor (N=31), and metastatic (Met, N=9) breast tissues. Moreover, to assess the contribution of environmental contaminations, several negative controls were used, including extraction buffer (EB, N=30), extraction room and gloves (ERG, N=4) harvesting room (HR, N=7), harvesting room gloves (HRG, N=10); homogenization buffer (HB, N=26), processing forceps (PF, N=6), processing room (PR, N=6); smart control (SC, a control included in the sequencing library generation kit, N=13). Furthermore, we examined all the nine hypervariable regions of the 16S rRNA to determine any technical influence on the microbiome analysis.