Revolution in the land of the microbiota! Following on from the intestinal, vaginal, respiratory and skin microbiota …a "new kid on the block" has just been discovered, to everyone's surprise, including and above all the researchers: the urinary microbiota.
We think of urine as sterile: but that's not true - it contains, even for those in good health, bacteria that definitely have a protective role in the bladder. Just like in the vagina or intestine, where some bacteria play a protective role by restricting undesirable growth or adhesion.
Discovering the urinary microbiota
It was not long ago that we couldn't analyse the bacterial "content" of urine except by culture growth which has its limitations... so we were unable to detect non-cultivable bacteria (due to specific characteristics or being present in too low quantities).
We are dealing with the cutting-edge technologies of molecular biology, which now enable us to confirm the microbial presence within urine by detecting their genetic sequences. The first study was in 2012 and since 2014 many publications have "refined" the results.
We can estimate that the diversity of urinary microbiota is comparable to that of the vaginal microbiota. The great majority are lactobacilli (almost 50%). But also bifidobacteria (about 12%) and potentially pathogenic bacteria including Escherichia coli (almost 2%).
Siddiqui H et al. Assessing diversity of the female urine microbiota by high throughput sequencing of 16S rDNA amplicons. BMC Microbiol. 2011 Nov 2;11:244.
A protective role?
Just like the intestinal microbiota, the urinary microbiota may have a potential role in urinary tract balance*:
By producing antimicrobial compounds;
By competing for "dietary" resources with pathogenic bacteria;
By activating the local and general immune system;
By maintaining the seal of the mucosa;
By breaking down toxic compounds.
* Whiteside SA, Razvi H, Dave S, Reid G, Burton JP. The microbiome of the urinary tract--a role beyond infection. Nat Rev Urol. 2015 Feb;12(2):81-90.
Urinary discomfort? Core requirements... the dysbiosis path
As also happens in the intestine or vagina, when the bacterial populations normally present are displaced by others, creating a variety of discomforts where the onset of "dysbiosis" is today recognised (irritable bowel, candidiasis, mycosis...), there may also have been a "take over" in the bladder by bacteria normally in the minority.
This will be the case for the well-known bacteria "Escherichia coli", a source of urinary discomfort particularly for women.
Studies also indicate that some bacterial strains will be more frequently present in women presenting with urinary incontinence, and that in cases of mictional urgency (or a compelling need to empty the bladder) we observe the significant presence of certain bacterial groups. A new era of research is therefore opening up, with the awareness of the urinary microbiota and its imbalances. Paths to be followed...
Now identified, the urinary microbiota can no longer be ignored; it plays a part in urinary tract balance.
And don't forget the interdependence of these microbiotas: intestinal, vaginal for women and in the bladder. We therefore find a strong degree of homology between the bacteria of the intestinal and vaginal microbiotas. A recent publication even shows that a vaginal bacteria Gardnerella vaginalis can "invade" the urinary tract via sexual activity and "wake up" Escherichia coli in the bladder*! The balance of one environment therefore has an effect on the balance of another, as is well-known for the vaginal and intestinal microbiotas.
So, even though there is still a lot to be discovered about bacteria in the bladder, it is up to us all to maintain their populations, notably via the regular intake of lactobacilli and bifidobacteria, the dominant bacteria in a "healthy" individual.