What changes occur to the bladder microbiome after SCI?

Authors: Sharon Jang , Vanessa Mok , Dominik Zbogar | Reviewer: Phillip Popovich | Published: 5 May 2020 | Updated: ~

Illustration accompanying What changes occur to the bladder microbiome after SCI?

Previously, it was thought that urine was clean and sterile – that urine should be free from bacteria and white blood cells, which are both signs of infection. In recent years, researchers have discovered that healthy urine is not always sterile. In a conditioned called

asymptomatic bacteriuria

,

non-harmful bacteria are found in the urine, but the individual does not experience any symptoms of a

urinary tract infection

(UTI)

or other illness. Although certain strains of bacteria in urine may be healthy, after SCI, the proportion and composition of bacteria found in urine changes. One (weak evidence) study suggests that individuals with SCI and neurogenic bladders have microbiomes with more unhealthy bacteria, which may be a precursor for UTIs.

With the knowledge that pre-existing bacteria live in the bladder, some researchers have questioned whether it would be possible to modify the microbiota to prevent UTIs. Bacterial interference is a process whereby non-harmful bacteria are injected into the bladder. Ideally, the benign bacteria prevent the growth of harmful bacteria by creating competition for nutrients and space to colonize. Multiple studies (weak evidence) indicate bacterial interference may decrease the occurrence of UTIs in individuals with SCI, and may delay the recurrence of UTIs. However, there are barriers to using bacterial interference, including:

  • The process of injecting bacteria into the bladder, which is a cumbersome process that requires multiple administrations over consecutive days.
  • The maintenance of the injected bacteria, which may not successfully colonize the bladder.

Given these limitations to bacterial interference in the bladder, other researchers have attempted to change the microbiome through indwelling catheters. Individuals who use indwelling catheters are at risk for UTIs, as bacteria can grow in the catheter and make its way back up into the bladder. To counter this, some researchers have observed the impact of coating indwelling catheters with non-harmful bacteria in attempts to reduce rates of UTI. Using the concept of bacterial interference again, the purpose of coating an indwelling catheter is to prevent harmful bacteria from growing inside it, thus preserving the bladder microbiota. These studies (weak evidence) found this method decreased the average number of UTIs experienced per year, and that using bacterial interference in catheters is a successful strategy for preventing the growth of harmful bacteria.

Refer to our chapter on Urinary Tract Infections for more information on reducing UTI risk for individuals with SCI.

Changes to the vaginal microbiome after SCI

The vaginal microbiota is primarily dominated by Lactobacilli bacteria, which act as a first line of defence against harmful bacteria. This is done by Lactobacilli creating an acidic environment, competing for nutrients and growth sites, and stimulating the immune system. As a result, the vagina is protected from the growth of harmful bacteria, including those causing sexually transmitted infections (STIs). In one study (weak evidence), researchers found that women with SCI have less Lactobacilli bacteria and more bacteria associated with UTIs and yeast infections.

Overall, there is limited evidence demonstrating microbiome differences in the urinary and reproductive systems of people with SCI. More research is needed to determine the implications of these variations and whether intervention is beneficial or necessary.