Urinary Tract Infection (UTI)
Biology and Development of Urinary Tract Infections
A UTI typically arises when microorganisms like bacteria or fungi enter the urinary tract through the urethra (Hooton 2012). UTIs can also occur in association with use of urinary catheters, which are medical devices that drain the bladder (Hooton 2010; Medline Plus 2011b).
There are many different bacteria that can cause UTIs, with Escherichia coli (E. coli) being the most common (Ronald 2002; Ferri 2011). Less commonly, fungi (esp. Candida species) may cause UTIs; this is more frequent in hospital settings or individuals with predisposing diseases and/or structural abnormalities of the urinary tract (Ronald 2002; Wildenfels 2010; Fisher 2011).
The bacteria that cause UTIs are similar to those naturally found in the colon and other areas of the body, but they have some characteristics that allow them to cause UTIs (Hooton 2012). One of the most important, especially in the case of E. coli, is the ability of these bacteria to adhere to the mucous membranes in the urinary tract (Schoolnik 1989; National Kidney and Urologic Diseases Information Clearinghouse 2012a; Roberts 1987). The mucous membranes of the lower urinary tract contain a variety of molecules, including mannose, a sugar. Strains of E. coli can adhere (or attach to) these mannose molecules using small projections, called fimbriae (Roberts 1987; Klemm 2010; Ohlsen 2009; Ermel 2012; Jorgensen 2012). This binding prevents bacteria from being cleared from the urinary tract by the flow of urine, which is normally a deterrent to bacterial colonization (Mulvey 2002). Once the bacteria have bound to the cells that line the urinary tract, they may then invade these cells. This process also helps the bacteria avoid being killed by antibiotics or the immune system (Jorgensen 2012; Mulvey 2001, 2002; Dhakal 2008).
Although most research has focused on E. coli infections of the urinary tract in otherwise healthy individuals, the general process is similar for other forms of UTI (Reid 1996). In the case of catheter-associated UTIs, which account for up to 40% of hospital-acquired infections, bacteria can gain access to the urinary tract via the catheter itself (Hooton 2010).