Urinary tract infections (UTI) are among the most common human infections and may have serious sequelace. Most UTI are caused by members of the bacterial family Enterbacteriaceae. UTI results from the interaction of Bacteria with a susceptible host. Each step in the pathogenic process is determined by the balance between host. Each step in the pathogenic process id determined by the balance between host resistance and bacterial virulence. The virulent strain possesses determinants required to colonize the bowel, ascend into and persist in the urinary tract and induce infection. The object of this research is to characterize and compare, using modern genetic techniques, bacterial genes that encode virulence determinants and to demonstrate the role of these virulence genes in UT1. More specifically, a variety of methods will be used for the genetic, physical and functional analysis of receptor specific proteins that mediate adherence of Proteus mirabilis and Escherichia coli to human uroepithelium.