Urinary tract infections (UTIs) are most frequently seen infections in clinical practice whether acquired in the community or hospital. The urine normally is sterile but whenever infection occurs it leads to inflammation of the uroepithelium resulting in bacteriuria and pyuria, though there are studies that show that the bacteria may be present in the uroepithelium even in the absence of bacteriuria. Bacteria may also be present if the urine gets contaminated during collection by organisms from skin, urethra, prepuce or introitus.
Virulence is the armor that the bacteria carry on them in order to cause disease by invading and establishing themselves in the host urinary tract. Amidst the virulence factors like motility, enzymes, serum resistance factor, toxins are the other important agents produced by the bacteria to inflict injury to the host. Concept of significant bacteriuria, pathogenesis and bacterial virulence, bacterial virulence, and future consideration with some other important topics are also discussed in this chapter.