Is the bladder microbiota responsible for recurrent urinary tract infections in postmenopausal women?

Why are postmenopausal women more susceptible to recurrent urinary tract infections? Is there an alternative to antibiotics, which give unsatisfactory results? To answer these questions, American researchers unveil a promising avenue: the bladder microbiota (or urinary microbiota).

 

Lower (cystitis) and upper (pyelonephritis) urinary tract infections are generally attributed to the migration of harmful bacteria from the anus towards the vagina and then the bladder. They are a true health scourge as they affect at least 150 million women worldwide each year, and particularly postmenopausal women: their relapse rate* reaches 55% versus 16 to 36% in premenopausal women. The only available treatment is long-term antibiotic therapy. Unfortunately, it is often ineffective and poorly tolerated by elderly women, does not prevent relapses, and contributes to antibiotic resistance.

Unusual bacteria

To understand the underlying mechanisms, an American team conducted analyses in 14 concerned postmenopausal women. Bladder biopsies revealed the presence of several bacterial species, as far as the deepest layers of the bladder wall. Besides known urinary pathogens frequently observed in premenopausal women (mainly Escherichia coli), the researchers discovered species rarely associated to urinary tract infections. They believe them to be true “relapse reservoirs” that are potentially responsible for treatment resistance.

More specific defense mechanism

The body’s immune response seems to play a key role in the predisposition of postmenopausal women to recurrent urinary tract infections. But contrary to observations made in mice, chronic inflammation of the human bladder wall triggers an adaptive immune response, i.e. a second line of defense which is more specific and involves cells specializing in target recognition.

Multiple factors

Although this study partly explains underlying mechanisms, the role of the bacteria involved in the urinary microbiota has yet to be elucidated, as well as that of inflammatory process and adaptive immunity. And it should be reminded that there are other risk factors: number of pregnancies, menopause-associated hormonal changes (estrogen deficit) and presence of some bacteria in the vaginal flora.

 

*Relapses are defined by more than 3 uncomplicated episodes per year or at least 2 in a 6-month period.

 

Sources:

N.J. De Nisco, M. Neugent, J. Mull, et al. Direct Detection of Tissue-Resident Bacteria and Chronic Inflammation in the Bladder Wall of Postmenopausal Women with Recurrent Urinary Tract Infection. Journal of Molecular Biology, https://doi.org/10.1016/j.jmb.2019.04.008