The microbiota isolated from the urine of patients with bladder carcinoma shows a significantly higher compositional abundance of some bacterial genera compared to the urine of healthy patients. Our objective was to compare the microbiota composition of cancerous tissues and urine samples collected from the same group of patients to improve the precision of diagnostic measures.

Tissue samples were collected from patients during the removal of cancerous tissue by transurethral resection. In parallel, urine samples were obtained by means of a transurethral resectoscope from the same patients. The V3-V4 region of the bacterial 16S rRNA gene was sequenced and analyzed using the Kraken pipeline. In the case of four patients, the duplicate microbiota analysis of distant parts of the cancerous tissues was highly reproducible and independent of the tissue collection site from any given patient. Akkermansia, Bacteroides, Clostridium sensu stricto, Enterobacter, and Klebsiella, as “five suspect genera”, were overrepresented in tissue samples compared to urine.

To our knowledge, this is the first study to compare the microbiota profiles associated with the urinary and bladder mucosa in patients with bladder cancer. A more precise characterization of the changes in the composition of the microbiota during the progression of bladder cancer could provide new opportunities in the development of adequate detection or monitoring methods.

Introduction

Bladder cancer is the ninth most frequently diagnosed cancer worldwide, with 75% of cases in men. Although the main risk factor for bladder cancer is smoking, exposure to aromatic amines or environmental factors such as arsenic in drinking water has been classified as additional carcinogenic risks. Additionally, genetic factors, including slow acetylation of N-acetyltransferase, a key enzyme in aromatic amine metabolism, are believed to play a role in the development of bladder cancer.

Urine was traditionally considered sterile; however, recent evidence has challenged this dogma by detecting molecule-based microorganisms in the urine of healthy individuals. Although the presence of microbes in the urinary tract does not necessarily induce infections, some microbial agents cause acute infection or chronic inflammation. Similarly, certain commensal strains can control the overgrowth of pathogenic bacterial strains.

The association between schistosomiasis infection of the bladder, inflammation, and squamous cell carcinoma is well accepted, but the role of bacteria in the pathophysiology or treatment of bladder cancer has not been consistently examined. In addition to the genetic characteristics that influence the elimination of chemical carcinogens, the processes can be aggravated or attenuated by the presence of biochemically active microbes.

For example, nitrate-producing bacteria can mediate the formation of carcinogenic N-nitrosamines. Toxins including heavy metals, pesticides, ochratoxins, polycyclic aromatic hydrocarbons, or other environmental pollutants are removed from the bloodstream by kidney filtration. All of these compounds interact with the microbiota during subsequent storage in the bladder. The resulting metabolites can increase or decrease the risk of bladder cancer.

Several factors can influence the difference in the incidence and progression of bladder cancer between men and women. The study by de Jong et al. described that male hormones can influence the type of bladder cancer a patient develops. The urinary microbiota is different in men and women.

Anatomical and hormonal differences lead not only to a higher incidence of female urinary tract infections but to different compositions of the urinary microbiota between the sexes. The incidence of female bladder cancer is significantly lower compared to male bladder oncogenesis. The different microbiota may be one of the hypotheses for the lower incidence of bladder cancers in women.

The urinary microbiota associated with benign urological conditions of transurethral catheter urine or evacuated urine was reviewed in detail. In women, evacuated urine samples contained mixtures of genital and urinary tract bacteria; however, uncultured bacteria, evaluated by 16S rRNA gene sequencing, were common in evacuated, transurethral catheterized, or suprapubic aspirated urine samples. In men, patients with or without lower urinary tract symptoms evacuated urine does not adequately characterize the microbiota of the male bladder.