Like other urinary tract infections, a bladder infection is typically caused by bacteria within the bladder. This is caused by bacteria (usually E. coli) entering through the urethra and moving to the bladder. Of course, E. coli is naturally present in the large intestine, so it comes out in our poo. So there’s the issue. Infection causing bacteria is naturally occurring in one system, super close to another system where we DO NOT WANT IT.