Urinary tract infections (UTI's) are common and annoying. They are generally caused by an overgrowth of bacteria in the urethra/urinary tract - commonly the culprit is E.coli. Usually there should be a relative abundance of good bacteria - Lactobacillus - which keeps the E.coli at bay, however when this bacterial balance becomes imbalanced, E.coli can overgrow and a UTI can rear it's head.