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I Zolfaghar, PJ Kang, EJ Lee, SM J Fleiszig; Involvement of Twitching Motility in Pseudomonas Aeruginosa Corneal Infection . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1597.
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Purpose: Previous studies have implicated pili of Pseudomonas aeruginosa as important virulence determinants. Our previous studies have shown that mutants of cytotoxic P. aeruginosa strain PA103 lacking assembled extracellular pili exhibit dramatically reduced cytotoxic activity. One role of pili is twitching motility, a form of bacterial cell movement resulting from the extension and retraction of the pilus filament. The aim of this study was to decipher the role of twitching motility in pathogenesis for PA103, a virulent stain that lacks flagella. Methods: A tw mutant (tw-) was isolated from a Tn5 transposon library of PA103 in which the transposon inserted in a gene encoding a putative histidine kinase. This mutant was found to have similar levels of extracellular pilin molecules as wild-type PA103. In vitro cytotoxicity of the mutant was compared to wild-type PA103 using LDH release assays and video microscopy. Virulence was compared using a murine model for corneal infection. Results: The tw- mutant had markedly reduced ability to kill corneal epithelial cells compared to wild-type PA103 as determined by LDH release (p<0.0001). Time lapse video microscopy showed that both wild-type PA103 and the tw- mutant could kill selected cells after accessing their basolateral membranes. The tw- mutant, however, had a reduced ability to move along the underside of adjacent cells, resulting in foci of dead cells that were much smaller in size. The tw- mutant was virulent, but caused less severe disease than wild-type bacteria. Furthermore, the appearance of the disease differed; the mutant caused patchy opacities, whereas wild-type infections were diffuse. Viable counts of corneas infected with the mutant showed normal colonization levels 4 h after inoculation (p=0.1831), but not after 48 hours (p=0.03). Conclusion: The data indicate that while twitching motility is not neccessary for the induction of cytotoxicity or disease, it may play a role in advancing these processes by allowing the bacteria to spread through the tissue.
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