The Microbiome of the Prostate Tumor Microenvironment

Background: The advent of molecular-based methods of identification and characterization of complex microbial populations has led to a new era of microbial discovery. A detailed and comprehensive analysis of the microbial ecosystem of the pathologic and healthy prostate tissues has not been yet reported.

Objectives: To characterize the microbiome possibly associated to the pathologic prostate microenvironment.

Design, setting, and participants: The microbiome profile of tumor, peri-tumor, and nontumor tissues was assessed on 16 radical prostatectomy-specimens.

Outcome measurements and statistical analysis: Microbiome analysis was assessed by massive ultradeep pyrosequencing. Bacteria load was expressed as a percentage of the total number of bacteria. The statistical significance of differences among specimen-groups was tested with Friedman's test (Dunn posthoc test) and Wilcoxon rank-sum test.

Results and limitations: Three phyla, six classes, nine orders, 14 families, and 11 genera were above the set threshold value of 1%, respectively. Significant differences in specific microbial populations among tumor/peri-tumor and nontumor prostate specimens were observed at certain taxonomic levels. Among genera, Propionibacterium spp. were the most abundant. Staphylococcus spp. were more represented in the tumor/peri-tumor tissues (p<0.05). The restricted number of specimens represents a potential limitation.

Conclusions: The prostate contains a plethora of bacteria, which set themselves within the gland with a distribution dependent on the nature of the tissue, thus suggesting a possible pathophysiological correlation between the composition of the local microbial niche and the presence of the tumor itself. Future studies will help to clarify the role of these specific bacteria and their potential to be exploited as new biomarkers.

Patient summary: The pathological prostate is populated by specific microbial populations, whose distribution varies according to the nature of the tissue. This finding opens interesting perspectives for the identification of novel therapeutic approaches and biomarkers.