EXECUTIVE SUMMARY
Almost half of all women will experience urinary tract infections (UTIs) in their lifetimes. Even with treatment, some 25% will develop recurrent infections within six months of initial infection.
- New research uncovered a trigger of recurrent UTIs — a type of vaginal bacteria that moves into the urinary tract.
- Experts recommend a three-day antimicrobial regimen for uncomplicated acute bacterial cystitis in women; bacterial eradication rates are marked consistently higher than 90%.
Almost half of all women will experience urinary tract infections (UTIs) in their lifetimes.1 Even with treatment, some 25% will develop recurrent infections within six months of initial infection.2
How can clinicians end this cycle of infection? New research from Washington University School of Medicine in St. Louis uncovered a trigger of recurrent UTIs — a type of vaginal bacteria that moves into the urinary tract.
E. coli causes about 80% of UTIs in young, sexually active women. The belief is that recurrence takes place when E. coli is reintroduced into the urinary tract; however, new research indicates another way for a subsequent UTI to develop. The Washington University School of Medicine research team’s work points to a vaginal bacterium, Gardnerella vaginalis.
“We found that a particular vaginal bacterium, Gardnerella vaginalis, did not cause infection during exposure to the urinary tract, but it damaged the cells on the surface of the bladder and caused E. coli from a previous UTI to start multiplying, leading to another bout of disease,” says Amanda Lewis, PhD, assistant professor of molecular microbiology and of obstetrics and gynecology at Washington University and the study’s senior author.
Study the Research
As part of the study, scientists infected the bladders of female mice with E. coli to initiate UTIs, and then allowed the infections to clear. One month after infection, no E. coli was detected in the animals’ urine. The researchers introduced into the bladders either Lactobacillus crispatus, a normal vaginal bacterium; G. vaginalis, which is associated with bacterial vaginosis; or sterile saltwater, which was used as a control.
Both types of vaginal bacteria were eliminated from the bladder within 12 hours. Data indicate this was enough time for E. coli to reappear in the urine of more than half the mice exposed to G. vaginalis, indicating a recurrent UTI. Mice given the normal vaginal bacteria or sterile saltwater were about five times less likely to develop another infection, compared with those given G. vaginalis.3
In some mice with G. vaginalis, researchers reported bacteria traveled from the bladder, through the urinary tract, to the kidneys. Although just 1% of women with bladder infections develop kidney infections, such infections can involve serious symptoms, such as back pain, fever, nausea, and vomiting. All the mice that received either G. vaginalis or E. coli in their urinary tracts showed some degree of kidney damage, but of the mice that received both species, 6% showed severe kidney damage, high levels of E. coli in the kidney, and signs that E. coli had moved from the kidney to the bloodstream. This finding may indicate the presence of G. vaginalis made E. coli more likely to cause severe kidney disease, researchers surmised.
“If a clinical lab finds G. vaginalis in a UTI sample, perhaps they shouldn’t assume it’s just a contaminant from the vagina,” notes contributing author Nicole Gilbert, PhD, an obstetrics and gynecology instructor at the university. “Our results suggest it could be contributing to the disease.”
What’s the Next Step?
More clinical studies are needed to inform doctors treating women for kidney infections to see whether bacterial vaginosis may be putting them at greater risk for this severe form of UTI. Although UTIs and bacterial vaginosis are treatable with antibiotics, different types are required. Standard antibiotics used for UTIs will not rid a patient of G. vaginalis.
Experts recommend a three-day antimicrobial regimen for uncomplicated acute bacterial cystitis in women; bacterial eradication rates are marked consistently higher than 90%. Use of trimethoprim-sulfamethoxazole for three days is considered the preferred therapy, with a 94% bacterial eradication rate. However, in areas in which resistance to this antimicrobial agent exceeds 15-20%, clinicians should choose another regimen. Other medications that have shown equivalency include trimethoprim alone, ciprofloxacin, levofloxacin, norfloxacin, and gatifloxacin.4
The Washington University findings also may explain why some women experience recurrent UTIs after having sex.
REFERENCES
- Foxman B. Epidemiology of urinary tract infections: Incidence, morbidity, and economic costs. Dis Mon 2003;49:53-70.
- Foxman B. Urinary tract infection syndromes: Occurrence, recurrence, bacteriology, risk factors, and disease burden. Infect Dis Clin North Am 2014;28:1-13.
- Gilbert NM, O’Brien VP, Lewis AL. Transient microbiota exposures activate dormant Escherichia coli infection in the bladder and drive severe outcomes of recurrent disease. PLoS Pathog 2017;13:e1006238.
- American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 91: Treatment of urinary tract infections in nonpregnant women. Obstet Gynecol 2008;111:785-794.
New research uncovered a trigger of recurrent urinary tract infections — a type of vaginal bacteria that moves into the urinary tract.
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