Urinary microbiome in non-muscle invasive bladder cancer: impact of sample types and sex differences

Previous research on urinary microbiomes in bladder cancer patients has yielded inconsistent results, highlighting the need for further investigation. This study aims to analyze microbiome dysbiosis in bladder cancer patients by comparing multiple sample types, incorporating negative controls, and assessing sex-based variations. Fifty patients who required transurethral resection of bladder tumor for treatment were selected. Three types of specimens were collected from each patient: midstream urine, catheterized urine, and normal bladder mucosal tissue. Microbiome was analyzed via 16 S rRNA gene amplificon sequencing.

Beta diversity analysis revealed significant differences in microbiome composition between mucosal tissue and urine samples, while no significant variation was observed between midstream and catheterized urine samples. Due to the low biomass of mucosal tissue-characterized by dominance of a few taxa and high variability across extraction kit lots-its susceptibility to contamination compromised reproducibility, leading to a focus on urine samples for further analysis. Midstream urine samples showed significant sex-related microbiome differences, whereas catheterized urine exhibited no such differences, suggesting midstream urine may not be ideal for bladder-specific microbiome studies. Catheterized urine analysis identified Curvibacter, particularly Curvibacter gracilis, as significantly more abundant in bladder cancer patients compared to controls, while overall microbiome composition remained unchanged between the groups. Curvibacter prevalence was not directly correlated with any single clinical marker but increased with bladder cancer severity when patients were classified into high-risk and low-risk groups based on biopsy and clinical criteria.

This study highlights the importance of selecting appropriate sample types for bladder microbiome analysis, with catheterized urine emerging as the most reliable option. The findings suggest that Curvibacter may be associated with bladder cancer severity, warranting further investigation into its potential role as a biomarker. Future research should focus on validating these findings in larger cohorts and exploring the mechanistic link between microbiome alterations and bladder cancer progression.