At the risk of being the “ackshally” guy, even indwelling catheters substantially increase the likelihood of bacteriuria, or abnormal bacteria in the urine. It gives motile bacteria additional surface area on which to make their way up the ureter, plus the initial placement can introduce microbes.

Bladders are pretty well colonized with a plethora of microbes. Short of nuking it with bleach, it’s never going to be sterile.

Relevant articles:

Catheter-associated urinary tract infection in adults

The bladder is not sterile: History and current discoveries on the urinary microbiome