The induction of cascades of virulence factors after contact between bacteria and host cells was investigated. P-pili mediate the binding of uropathogenic Escherichia coli to its host cell receptor, After P-pili binding there was transcriptional activation of a sensor-regulator protein that is essential for the bacterial iron-starvation response, An insertion mutation of the sensor-regulator gene eliminated the ability of uropathogenic E, coli to produce siderophores and their iron-regulated membrane receptors, thereby abolishing their ability to grow in urine, These results suggest that P-pilus-mediated attachment may be an important part of the sensor-regulatory process involved in uropathogenic E. coli urinary tract infection.