Gardnerella Vaginalis in Recurrent Urinary Tract Infection is Associated with Dysbiosis of the Bladder Microbiome

Background: Recent studies on the urine microbiome have highlighted the importance of the gut-vagina-bladder axis in recurrent cystitis (RC). In particular, the role of Gardnerella as a covert pathogen that activates E. coli in animal experiments has been reported. Herein, we conducted a human bladder microbiome study to investigate the effect of Gardnerella on RC. Methods: Urine 16S ribosomal RNA gene sequencing via transurethral catheterization was conducted in the normal control group (NC) (n=18) and RC group (n=78). Results: The positive detection rate of Gardnerella species did not differ between the NC and RC groups (22.2% vs. 18.0%, p = 0.677). In addition, the Gardnerella-positive NC and Gardnerella-positive RC groups showed similar levels of microbiome diversity. The Gardnerella-positive group was categorized into three subgroups: Escherichia-dominant group, Gardnerella-dominant group, and Lactobacillus-dominant group, respectively. All of the Escherichia-dominant groups were associated with RC. Gardnerella-dominant or Lactobacillus-dominant groups expressed RC with symptoms when risk factors such as degree of Gardnerella proliferation or causative agents of bacterial vaginosis were present.Conclusion: Gardnerella can act as a covert pathogen of RC depending on other risk factors, and Gardnerella infection should be considered in patients with RC. New guideline recommendations regarding antibiotics selection based on a novel method to detect the cause of RC may be required to reduce antibiotics resistance.