Whether from endogenous or exogenous sources, infecting microorganisms gain access to the urinary tract by several routes. Microorganisms that inhabit the meatus or distal urethra can be introduced directly into the bladder when the catheter is inserted. However, microorganisms introduced by this method are usually removed from healthy individuals by voiding or by antibacterial mechanisms of the bladder mucosa . With indwelling catheters, infecting microorganisms can migrate to the bladder along the outside of the catheter in the periurethral mucous sheath or along the internal lumen of the catheter after the collection bag or catheter-drainage tube junction has been contaminated .