Bacteria responsible for recurrent urinary-tract infections migrate from the gut.
These infections, which affect up to one-quarter of women, are caused mostly by strains of the bacterium Escherichia coli that are thought to give up their adaptations to life in the gut for ones that allow them to thrive in the urethra and bladder. A team led by Jeffrey Gordon at Washington University in St. Louis, Missouri, compared the genomes of dozens of E. coli strains from the faeces and urine of four women with recurrent infections.
In two of the women, new but matching E. coli strains emerged in both the gut and the urinary tract. Follow-up experiments in mice showed that the same strain could survive at both sites without the expected loss of fitness. Strategies to fight recurrent infections might need to be reconsidered, the authors say.