what causes bladder infection
1 Infection of the bladder (cystitis). 2  This type of UTI is usually caused by Escherichia coli (E. coli), a type of bacteria commonly found in the gastrointestinal (GI) tract. 3  However, sometimes other bacteria are responsible.4  Sexual intercourse may lead to cystitis, but you don't have to be sexually active to develop it. Infection of the urethra (urethritis). 2  This type of UTI can occur when GI bacteria spread from the anus to the urethra. 3  Also, because the female urethra is close to the vagina, sexually transmitted infections, such as herpes, gonorrhea, chlamydia and mycoplasma, can cause urethritis.