Twitching Motility Contributes to the Role of Pili in Corneal Infection Caused by Pseudomonas aeruginosa

Twitching motility is a form of surface-associated bacterial movement mediated by type IV pili of Pseudomonas aeruginosa. Others have shown that pilT and pilU mutants, which are piliated but defective in twitching motility, display reduced cytotoxic capacity towards epithelial cells in vitro. Although these mutants efficiently infected lungs in vivo, they were defective in dissemination to the liver. In this study the role of twitching motility in P. aeruginosa epithelial cell invasion and corneal disease pathogenesis was explored. pilU and pilT mutants of P. aeruginosa strain PAK were compared to a nonpiliated pilA mutant and to wild-type bacteria in their ability to associate with and to invade corneal epithelial cells in vitro and to cause disease in a murine model of corneal infection. As expected, the pilA mutant demonstrated reduced association and invasion of corneal epithelial cells (P < 0.05 in both cases). The pilT mutant, but not the pilU mutant, was less invasive than wild-type PAK was (P < 0.05 versus P = 0.43), while both pilU and pilT mutants exhibited association levels similar to those of the wild type (P = 0.31 and 0.52, respectively). In vivo, all mutants were markedly attenuated in virulence and showed reduced ability to colonize the cornea at 4 and 48 h (all P values < 0.02). Thus, twitching motility contributed to the role of pili in corneal disease but was not involved in the role of pili in adherence to or invasion of corneal epithelial cells.