Escherichia coli or the influence of intestinal microbiota on urinary tract infections
Due to anatomical reasons, women are much more prone to urinary tract infections (UTI) than men. The most frequent form in women is cystitis, a bladder infection caused by the bacterium Escherichia coli.
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Escherichia coli is naturally present in our intestinal microbiota but can become a pathogen by using some of its infectious properties such as the ability to adhere to the bladder. It is then referred to as uropathogenic Escherichia coli (UPEC). Urinary tract infections occur when the urogenital area is contaminated by the fecal flora. Bacteria can colonize the urethra exclusively (causing urethritis), spread to the bladder and cause acute cystitis, or reach the kidneys (causing pyelonephritis). This bacterial migration from the anal area to the urogenital system raises two questions: are the responsible strains different from a genetic standpoint or do they need to adapt when they migrate from the intestines to the bladder? For preventive purposes, could it be possible to predict the risk of contracting a UTI using fecal Escherichia coli samples?
No adaptation is required
Several studies4, 5 from a Danish team provided us with some answers. The researchers observed that the fecal strains of Escherichia coli in patients with UTI were the same as those found in their own urine samples and also the same as in healthy women. The only differences were a few minor genetic variations. In other words, Escherichia coli is able to migrate from the intestines to the bladder without needing to adapt at all. The evidence thus showed that fecal microbiota composition cannot predict the risk of developing a urinary tract infection. Then, what are the causes of UTIs? UPEC-mediated urinary tract infection probably results from a combination of factors related to the bacteria (ability to adhere to intestine cells, virulence...) and to the host’s immune status, creating an infection-prone environment
4. Nielsen KL, Stegger M, Kiil K, et al. Whole-genome comparison of urinary pathogenic Escherichia coli and faecal isolates of UTI patients and healthy controls. Int J Med Microbiol. 2017 Dec;307(8):497-507
5. Nielsen KL, Stegger M, Godfrey PA, et al. Adaptation of Escherichia coli traversing from the faecal environment to the urinary tract. Int J Med Microbiol. 2016 Dec;306(8):595-603