Does Gardnerella vaginalis Play an Important Role in Urinary Tract Infections?

A vaginal epithelial cell infected with multiple Gram negative and positive bacterial species including G. vaginalis, indicative of Bacterial Vaginosis (BV).

Urinary tract infections are a result of bacteria entering the urinary tract through the urethra. When these bacteria arrive at the bladder, they begin to multiply, leading to an infection. In most cases, the urinary system can usually fight off these invaders; but in cases where the defense of the urinary system fails, UTIs affect the bladder and urethra.

When the infection persists in the bladder, it is typically caused by Escherichia coli. This particular type of infection is referred to as “cystitis.” In cases where the infection is found in the urethra, a result of gastrointestinal (GI) bacteria spreading from the anus to the urethra, this particular type of infection is called “urethritis.”

While E.coli has historically been the primary culprit of UTIs, studies show that the vaginal bacterium, Gardnerella vaginalis, plays a significant role. G. vaginalis is a gram-variable, facultative anaerobic bacterium that is non-motile and non-sporeforming.  It is commonly associated with bacterial vaginosis (BV) when it persists in the vagina and overwhelms the healthy Lactobacillus population, especially in young, sexually active females. It is now accepted that Gardnerella vaginalis is not the sole cause of the condition, which is characterized by a reduction in the numbers of Lactobacilli and an increase in other bacteria including Gardnerella vaginalisBacteroidesspp, Mobiluncus spp,  anaerobic Streptococci, Mycoplasma hominis and Ureaplasma urealyticum. The term Bacterial Vaginosis better reflects the diverse vaginal microbiology of this dysbiotic condition. On a gram stain, a vaginal smear generally shows a shift from Gram positive to predominantly Gram negative bacteria.
Recent studies show that G. vaginalis aids E. coliin its infection of the bladder. Researchers at the Washington University School of Medicine in St. Louis infected bladders of female mice with E. coli to initiate UTIs. When these mice recovered from the infection after one month, their urine was screened for E. coli, but none were detected. This screening was performed because former studies had shown that some E. coli persist in the bladder even post-infection and are found in very low levels in urine. After the infection had cleared and no E. coli was detected in the urine, researchers introduced either lactobacillus crispatus or G. vaginalis, both residents of normal vaginal microflora, to the bladders of the mice. These bacteria were eliminated from the bladder within 12 hours of introduction. Interestingly, however, E. coli appeared in the urine of more than half of the female mice that were introduced to G. vaginalis.

A bladder epithelial cell (blue) that has been exposed to G. vaginalis is in the state of dying and detaching from its neighboring cells (teal), revealing immature cells below (purple). Credit: M. Joens, J. Fitzpatrick and N. Gilbert, Washington University, School of Medicine, St. Louis.

With further speculation, it appears that G. vaginalis plays a role in the recurrence or “awakening” of E. coli in the bladder and, thereby, aids in recurrent infections. One-quarter of women treated for UTI will experience a recurrence within six months.
It was found that some of the mice exposed to G. vaginalis had infections that moved from the bladder, up through the urinary tract, and into the kidneys, causing a kidney infection. Researchers at the university suggest that G. vaginalis may damage cells on the surface of the bladder, releasing the dormant E. coli housed in those bladders cells. As a result, when the dormant E. coli cells are liberated, they can begin to multiply and contribute to recurrent UTIs.
There are some major implications of this study which impact the diagnosis and treatment of UTIs. Of concern is the fact that the antibiotics commonly used to treat UTIs are not effective in eliminating G. vaginalis. 
Moving forward, it may be important for physicians and practitioners to consider a patient’s history of bacterial vaginosis and the presence of G. vaginalis in a UTI sample. Historically, G. vaginalis in a UTI sample may have been disregarded as a contaminant of the normal vaginal microflora. However, this study suggests that G. vaginalis may play a significant role in recurrent UTIs.

Reference for Washington University study
Reference from CDC on bacterial vaginosis

by Nasim Delavari, Technical service, Hardy Diagnostics (originally posted in MicroBytes, April 2017)

Hardy Diagnostics Gardnerella Selective Agar is selective and differential for the isolation of Gardnerella vaginalis from vaginal specimens.

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