Abstract
Urinary tract infections (UTIs) are one of the most common bacterial infections, affecting more than 150 million people each year in the world. UTIs have grown exponentially in the last few years. They represent a major load for both individuals and society. The highest incidence (about 55-60%) concerns women. Many pathogens are involved in UTIs, most of which are derived from the gut. Recent studies, together with recent diagnostic techniques (such as quantitative culture of urine or next-generation sequencing), have improved the knowledge of microbial communities in the urinary tract. It turned out that gut dysbiosis is strictly involved in the pathogenesis of UTIs. In particular, the human gut is the natural habitat for Escherichia coli (E. coli), the main bacterium responsible for UTIs. The overgrowth of E. coli pathogenic strains represents a risk factor for them. Furthermore, the human gut microbiota acts as a "global reservoir" for genes conferring resistance to clinically relevant antibiotics, thus influencing the treatment of UTIs. In addition, differently from the past, the idea of a sterile urinary environment has been replaced by the characterization of a urinary microbiome. The aim of our review is to explore recent studies on the association between gut microbiota and urinary microbiome and to summarize the current knowledge about the effects of interactions between gut and urinary microbial communities in the pathogenesis of UTIs, considering UTIs more as a "gut disease" and not only a urinary disease and providing new insight into the therapeutic options such as the use of probiotics.