Introduction
Urinary tract infections are prevalent worldwide, with Escherichia coli being the main causative agent affecting around 150 million people every year. The major risk factor includes a history of prior urinary tract infections. The pathogenesis involves the sequelae; at first, the periurethral space is contaminated, followed by urethral colonization, which later migrates to the urinary bladder. Studies conducted show that vaginal dysbiosis (a disruption in the vaginal microflora by diverse bacteria) may be a cause of the colonization of Escherichia coli.
What Is the Importance of Gut Microbes in the Urinary Tracts?
The gut microbiota helps influence the health of other organs along with the gut. They help maintain human psychological and physiological well-being as there is an association with the microbiota-gut-brain axis. Similarly, an association between the gut and the kidney indicates that the gut microbiome plays an important role in the gut-kidney axis. Studies have shown that disruption in the gut microbiome may lead to renal disorders, which further cause complications of hypertension, chronic kidney failure, and kidney stones.
Urinary tract infections begin with the contamination of the periurethral space by gut pathogens, proceeded by the urethra, and last by the migration to the bladder. 80% of community-acquired infections are due to Escherichia coli, the main causative agent of urinary tract infections. Staphylococcus, Klebsiella, Enterobacter, Proteus, and Enterococcus are associated with health-related infections.
The uropathogenic Escherichia coli has genes encoding for bacterial pathogenicity, that is, toxins, surface polysaccharides, adhesions, flagella, and iron acquisition factors. These factors are absent in commensal Escherichia coli. Urinary tract infections show a female predilection because the female urethra is shorter than the male urethra, which helps in the easier migration of pathogens to the urinary tract.
It was reported that breastfed infants and preterm neonates have a lesser incidence of urinary tract infections. A study conducted by Paalane et al. showed higher activity of Enterobacter in the gut of individuals with urinary tract infections when compared to healthy individuals.
Magruder et al. conducted a study where they described the association between gut microbiota and urinary tract infection. He stated that the increased activity of E.coli leads to the future development of E.coli bacteriuria and E.coli-induced urinary tract infection.
The strains of E.coli are similar to those of E.coli in the urine of the same individual. The study also stated that the two bacterial taxa, fecal bacteria and Enterobacteriaceae, can reduce the risk for Enterobacteriaceae bacteriuria and urinary tract infections in kidney transplant recipients.
Thaner et al. mentioned in their study that the intestinal bloom of uropathogens, followed by the repeated transmission of uropathogens between the gut and urinary tract, shows recurrent urinary tract infections.
What Is the Vaginal Microbiome?
Lactobacillus species such as L.crispatus, L.jensenii, L.gasseri, and L.iners are the dominating microbiome in women of reproductive age. These Lactobacilli produce lactic acid, which helps maintain the low ph of the vagina and produces antimicrobial compounds such as hydrogen peroxide and bacteriocins. Along with Lactobacillus, another diverse microflora is seen, including gram-negative anaerobic microorganisms such as Actinobacteria and Firmicutes. Certain bacterial species and microbial characteristics help prevent diseases of the urogenital tract. Women who have had a history of urinary tract infections harbor E.coli in their vaginal introitus.
A study conducted by Brannon et al. showed that E.coli adheres and invades the vaginal cells in acute and chronic urinary tract infections, proving its ability to reside inside the vagina after a urinary tract infection. This ability to colonize the vagina leads to recurrent urinary tract infections. E.coli can thrive in the vagina because of its ability to establish a vaginal intercellular reservoir that protects it from extracellular stressors. Women with Lactobacilli-dominated microbiomes have a lower risk of urinary tract infections as it has a protective role in preventing colonization of E.coli and other uropathogens. Women with low levels of Lactobacilli have a higher incidence of E.coli colonization.
What Is the Significance of the Urinary Microbiome?
The urinary microbiome plays a role in pathological conditions such as urge incontinence, overactive bladder, and urinary bladder cancer. Studies showed that individuals with lower diversity of microbial flora had a higher incidence of developing urinary tract infections than individuals with higher diversity of microbial flora. Bossa et al. demonstrated that the microbiome stabilizes after treating a urinary tract infection. Urinary tract dysbiosis (disturbance in the urinary microbiome) is suggestive of an upcoming urinary tract infection. Grine et al. stated that Methanobrevibacter smithii is a causative agent in community-acquired urinary tract infections. Persistent bladder colonization may lead to a chronic condition and is usually dominated by Corynebacteriaceae. Thomas White et al. stated that postoperative urinary tract infection is linked to the day of surgery microbiome of catheterized urine.
Can the Risk of Urinary Tract Infection Be Reduced?
Antibiotics are commonly recommended for urinary tract infections. The advancement in treatment involves precision antimicrobial therapeutics and UTI vaccines. Modulating the gut microbial community is essential as it is one of the major reasons for urinary tract infections. Commensal bacteria can be used as probiotics to stabilize the altered microbiome; a probiotic usually involve strains of Lactobacilli along with an extract.
This helps in lowering recurrent urinary tract infections. Fecal microbial transplantation has emerged as a promising treatment modality. Studies conducted on fecal microbial transplantation have shown an improved microbial susceptibility profile suggesting the decolonization of multidrug-resistant pathogens. It also showed a reduced rate of recurrent urinary tract infections. Hormone therapy may be suggested for postmenopausal women as a primary or secondary prevention mode. Vaginal estrogens help with urinary urgency, frequency, nocturia, and recurrent urinary tract infections. The prevention and treatment of urinary tract infections are dependent on the microbiome. The probiotics are administered to change the ratio between uropathogens and Lactobacillus.
Conclusion
Escherichia coli causes urinary tract infections found in the gut microbiome and can travel to the urinary tract causing infection. The major risk factor includes a history of prior urinary tract infections. The pathogenesis involves the sequelae; at first, the periurethral space is contaminated, followed by urethral colonization, which later migrates to the urinary bladder. Treatment modalities include antibiotic therapy, oral or vaginal probiotics, and hormonal therapy.
