Our body is home to, as you can imagine, a number of cells – and a number of types of cells (blood, nerve, etc.). It was thus estimated that a so-called “reference” human being (20 to 30 years old, 70 kg and 1.70 m) had approximately 3.1013, or 30 thousand billion cells.
What we know less is that we are also a prime host land for microbes, bacteria in particular! They would be nearly 3.9.1013, more than our own cells.
The importance of this microscopic population can make one dizzy… These high figures above all suggest an important role for the cohorts of bacteria, fungi and other viruses which colonize us.
Several parts or organs of our body are thus occupied by a “microbiota” – such as the intestine, whose associated microbiota has been the subject of in-depth studies. But if the latter’s composition and roles in health and disease are beginning to be better understood, other microbiota still largely fly under the radar. For example at the level of our skin, sperm for these gentlemen…
The urinary microbiota is also one of these illustrious quasi-unknowns. A mistake as its implications for health are numerous, as discovered by researchers from the University of Granada, Almeria and the Virgen de las Nieves University Hospital.
The urinary microbiota: a great unknown
For a long time, it was believed that the urine of healthy people was sterile; that the bacteria which could be found there could be the cause of local infections. This idea was supported by the use of bacterial culture techniques which only allowed the growth of a very limited number of microorganisms.
This is a mistake: urine is not sterile.
Genomics, the development of the Human Microbiome Project or new mass genetic sequencing tools have changed the situation: they have proven that there is a large microbial community also in the urinary tract of healthy individuals.
The first major observations can be made:
This particular ecosystem varies depending on the sex of the host: the major bacterial genus in women is Lactobacillus; in humans, much less studied, the urinary microbiota is dominated by the genera Corynebacterium and Streptococcus.
Age and hormone levels are capable of altering it, causing bacterial species to evolve. Over the years, for example, we have observed a decrease in Lactobacillus and Gardnerella and a proliferation of genera such as Mobiluncus, Oligella and Porphyromonas.
Many species specific to the urinary tract are not limited to this sector, but also inhabit the vagina and the intestine. Changes in these two bacterial communities also lead to changes in the urinary microbiota.
Its role in urinary tract diseases
Traditionally, urinary tract infection is associated with isolated pathogenic bacteria such as Escherichia coli. However, new research has identified a multiple origin, meaning that it is due more to a deterioration of the microbiota than to the invasion of a specific pathogen. In general, a reduction in Lactobacillus – still widely present in healthy individuals of both sexes – appears to increase the frequency of urinary infections.
Some of its alterations have also been associated with other pathologies such as urothelial carcinoma and prostate cancer. The increase in bacteria that secrete substances involved in inflammatory processes could promote the development of these diseases. The bacteria Streptococcus anginosus, of the genus Anaerococcus, are for example often involved in urogenital infections and can be more abundant in samples taken in cases of cancer.
And that’s not all: mechanical problems such as urinary incontinence can also be influenced by changes in the local bacterial community. Microbial depletion in healthy individuals often goes hand in hand with an increase in the population of pathogenic microorganisms, which release molecules promoting muscle contraction into the bladder – among other mechanisms.
These are just some of the diverse and varied conditions linked to the state of the urinary microbiota: these results therefore underline the importance of taking them into account in prevention, their diagnosis and their treatment…
A new field of study for new therapies
Today, most UTIs are treated with broad-spectrum antibiotics. However, the increasing emergence of bacteria resistant to these drugs shows how crucial it is to more precisely identify the causative pathogens.
Better identification will make it possible to better identify the antibiotics to be administered in order to obtain a precise action. On the one hand, this will avoid promoting the development of resistance in bacteria which were not involved in the disease and, on the other hand, it will prevent the deterioration of microbial communities present elsewhere in the human body.
The idea is also to develop new therapies, apart from antibiotics.
Probiotics, for example, live microbes (mainly bacteria) that can have beneficial effects on health, have attracted growing interest in recent years. Intravaginal or oral administration of certain Lactobacillus strains, such as L. crispatus and L. acidophilus, has resulted in long-term colonization of the urinary microbiota and a reduction in the incidence of infections.
Other therapies based on current knowledge of the urinary microbiota include fecal microbiota transplantation and the use of bacteriophages (viruses that infect and can kill specific bacteria). These two methods have helped reduce the prevalence of urinary infections and the presence of the responsible bacteria, including those with significant resistance to antibiotics.
Diet to maintain a healthy microbiota
But before getting there, we can also contribute very simply, through our habits, to keeping the microscopic population that colonizes our urinary tract stable and healthy.
As with other microbiota, diet plays an important role. Thus, moderate consumption of products containing cranberries, fermented foods rich in probiotics, etc. can help preserve our bacterial balance and eliminate pathogenic bacteria.
Although there is still a long way to go to understand it in depth, the urinary microbiome could be the key to developing new preventive, diagnostic and therapeutic strategies for diseases affecting the urinary system.
This article was written by researchers Virginia Pérez Carrasco, José Antonio García Salcedo, José Gutiérrez-Fernández and Miguel Soriano Rodríguez and was published on the website The Conversation.
