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D.J. Evans, I. Zolfaghar, A. To, S.M. Fleiszig; Twitching Motility Contributes to the Role of Pili in Corneal Infection Caused by Pseudomonas aeruginosa . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3240.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Type IV pili of Pseudomonas aeruginosa are thought to be important virulence determinants. One role of pili is twitching motility, a method of flagellum-independent surface associated movement. Both pilT and pilU mutants express pili, but are defective in twitching motility because of an inability to retract their pili. Unlike pilU and pilA mutants, the pilT mutant is also phage resistant. Both mutants demonstrate reduced adherence to, and cytotoxicity toward, three epithelial cell types and although they do not reduce the ability to cause lung disease in an animal model, they do affect the spread of bacteria to the liver. The aim of this study was to investigate the role of twitching motility in corneal infection by an invasive strain. Methods: Virulence of pilU and pilT mutants of PAK was compared to a non-piliated pilA mutant, and to wild type PAK, using a murine model for corneal infection. They were then compared for their ability to adhere to, and invade corneal epithelial cells in vitro. Results: The pilT mutant, but not the pilU mutant, was found to also lack flagella-mediated swimming motility. As expected, the pilA mutant demonstrated significantly reduced corneal epithelial cell invasion and association as compared to wild-type PAK (p < 0.05 in both cases). The pilT mutant, but not the pilU mutant, was defective in ability to invade (p = 0.0002 vs. p = 0.35), while adherence levels were similar to wild type PAK (p = 0.85). Interestingly, pilU mutant adherence was higher than that demonstrated by PAK (p = 0.018). In vivo, all three mutants were markedly reduced in their virulence as determined by severity scores, and in their ability to colonize the cornea by viable counts at 4 and 48 h (all comparisons to wild type were p ≤ 0.02). Conclusions: The results show that although pili are important for both corneal epithelial cell adherence and invasion, that contribution does not involve their twitching motility function. In contrast, twitching motility was found to be a major contributor to corneal disease in vivo. Taken together these results suggest that the role of twitching motility might be in bacterial penetration into the cornea, or in their ability to survive after penetration, rather than in early epithelial interactions.
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