E. Coli is responsible for 80–90% of UTIs in the general population. Logically, you would assume that recurrent UTIs following sex and other triggering activities like exercise or travel are the result of new bacteria being repeatedly introduced into the urinary tract. However, in many cases, this is not what is happening.
2. Bacterial biofilm and embedded UTIs
Antibiotics treatment doesn’t always clear an infection. Some bacteria can be left over. During an infection, bacteria can form biofilm on the bladder wall. Biofilm is a protective network of bacterial cells and secreted compounds that forms a shield that is difficult to penetrate. A tool implemented by bacteria in many infections, not just UTIs, biofilm can protect bacteria from the immune system and antibiotics, allowing them to stay dormant. Biofilms are difficult to detect, and urine cultures may also come up negative. At a later time, these shielded bacteria can release themselves from the biofilm, replicate, and cause a “new” infection. This cycle can continue, causing recurrent UTIs.
In this instance, what seems like a separate UTI is actually the same infection. Biofilms are now understood to play an important role in recurrent UTIs and may be why 30–44% of females with their first UTI will experience a second UTI within 6 months (1). But why, at least for many women, would these flare-ups continue to occur after sex if new E. coli isn’t being introduced? New research shows there may be an additional mechanism at work.
3. The Vaginal Microbiome and its effect on urinary tract health
The vaginal microbiome is a complex community of microorganisms that live naturally in the human vagina. Thanks to recent research, we have a new understanding of the role the vaginal microbiome plays in recurrent UTIs. Healthy vaginal microbiomes are dominated by a genus of bacteria called lactobacillus. Lactobacilli excrete lactic acid and hydrogen peroxide that keep the normal vaginal pH low. A low pH limits the growth of potentially pathogenic bacteria that occur naturally in the vagina. Rising pH can allow for the overgrowth of the “bad” bacteria.
One of these types of bacteria is Gardnerella vaginalis, the bacteria primarily responsible for Bacterial Vaginosis (BV), a common infection in women. In fact, the CDC estimates that 29.2% of all women ages 14–49 currently have BV, yet 84% of those women do not experience symptoms. BV, however, can be a major risk factor for UTIs (2).
In 2017, research was published demonstrating how this might happen. G. vaginalis from the vagina enters the urinary tract and disrupts and weakens the bladder wall, making it more vulnerable to infection by E. coli already present in the bladder from previous infections (4).
For women with recurring UTIs from sex, this could be the trigger. E. coli isn’t re-introduced; it is already there. A different bacterium, G. vaginalis, is transported to the urethra from the vagina during sexual activity, where it damages the cells of the bladder wall, giving the biofilm-protected E. coli their opportunity to multiply and cause another infection. This is especially likely if a woman suffers from BV, which may be asymptomatic.
Although this research was mostly referencing sex, it’s easy to imagine how this same cause-and-effect would take place for people who find that their UTIs are not linked to sex, but other activities or conditions, like diet or stress.
A Cycle of Infections
Antibiotics taken for UTI treatment can actually disrupt the vaginal microbiome, causing pH to rise, increasing the risk of BV (5). This may be why it is common for women with recurring UTIs to also experience recurrent BV. In turn, these vaginal infections are now known to increase risk of more recurrent UTI episodes, causing a cycle of infections.
In order to appropriately address recurrent UTIs caused by sexual activity, one must prioritize the health of the vaginal microbiome.
What this means for women with recurring UTIs from sex
For women with recurring UTIs from sex or other activities, this could be the trigger that has been difficult to find. E. coli isn’t re-introduced; it is already there. A different bacterium, G. vaginalis, is transported to the urethra from the vagina during sexual activity, where it damages the cells of the bladder wall, giving the biofilm-protected E. coli their opportunity to multiply and cause another infection. This is especially likely if a woman suffers from BV, which may be asymptomatic because G. vaginalis is present at higher concentrations. However, it is important to note that G. vaginalis occurs naturally in the vagina, potentially making these infections difficult to manage.
Final thoughts
It is important to note that the mechanism presented by the University of Washington researchers is likely just an example of one of many mechanisms by which embedded or newly introduced E. coli capitalize on a changing urogenital microbiome. Evidence is now strong that the urine is not sterile, and there is a complex microbiome present in the urine with many species of benign bacteria living naturally. There are complex microbiomes at work in the female vagina, the skin of the sexual partner, and the urinary tract that are constantly changing and rebalancing. Although research is still developing, the fact that the urogenital system is tightly connected is increasingly clear.
Research is still very early, and the models presented at this time are almost certainly simplified versions of reality. However, we do know that the vaginal microbiome and the health of the urinary microbiome are important to the mechanism of rUTI.
References
- Kramer, Melissa. Chronic urinary tract infection vs recurrent UTI. Live UTI Free. August, 2020.
- Bacterial Vaginosis (BV) Statistics. Centers for Disease Control and Prevention. Sept, 2020.
- Kline KA, Lewis AL. Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract. Microbiol Spectr. 2016; 4(2).
- 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 Mar 30; 13(3).
- Reid G. Probiotic agents to protect the urogenital tract against infection. American Journal of Clinical Nutrition. 2001 Feb; 73(2 Suppl):437S-443S.
