A differential bladder microbiota composition is associated with tumour grade in bladder cancer

Background Microbiota has been linked to the development of multiple cancers through various mechanisms. In bladder cancer (BC), preliminary studies have found alterations in the urinary microbiota of patients with urothelial carcinoma in comparison with healthy individuals. However, the bladder microbiota (BMi) has not been explored. The aims of this study were to characterize the BMi in a cohort of BC patients, to explore differences in the BMi composition between tumor (T) and normal (N) mucosa, and to identify its correlation with clinicopathologic features. Methods A total of 58 samples obtained by cystectomy from 32 BC patients (frozen tumor tissues and normal appearing mucosa for 26 patients and 6 tumor tissues) from Hospital General de Elche Biobank (Spain) were included. DNAs isolated from bladder samples were used to perform 16S rRNA gene sequencing (V3 and V4 region). A paired-end 2 × 300 bp cycle run on Illumina MiSeq. Ribosomal Database Project Classifier was used for taxonomical assignment. Statistical analysis was performed using Rstudio platform. Groups of data were compared using Wilcoxon test and Mann Whitney test for 26T vs 26N (paired group) and 32T vs 26N (unpaired group), respectively. Results There were no statistically significant differences of diversity between T and N, but there were differences of richness between T and N at the genus level (Chao1 index, p = 0.049). Globally, the most abundant phylum was Firmicutes, followed by Bacteroidetes, Proteobacteria and Actinobacteria. We found that the microbial composition differed significantly between T and N in both groups. At the phylum level, while Cyanobacteria.Chloroplast (0.74% vs 2.44%; p = 0.025) was enriched in T, Actinobacteria were reduced in T. Principal component analysis based on the relative abundance of phylum (36.9% PC1 and 28.7% PC2 of explained variance) revealed a significant separation in bacterial community composition between tumor tissues associated with histological tumor grade (permanova grade =0.036). Conclusions Significant differences in the BMi composition associated with tumor grade were observed. Additional studies are needed to determine the role of BMi in the evolution of BC and its therapeutic implications. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.