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Chairut Vareechon, Valerie Lozada, Jonida Toska, Stephanie Zmina, Eric Pearlman, Arne Rietsch; The ExoU genomic island is responsible for the greatly increased virulence of P. aeruginosa strain 19660 in the cornea.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):340.
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© ARVO (1962-2015); The Authors (2016-present)
The strain 19660 of P. aeruginosa contains an additional virulence factor, encoded on a genomic island that encodes for the gene for the type III-secreted effector ExoU, which contributes significantly to corneal disease severity. We hypothesize that deletion of only exoU from strain 19660 still results in a highly virulent strain, however; deletion of the entire genomic island that encodes for exoU will result in virulence that is significantly reduced that is highlighted by a decrease in corneal opacity and colony-forming units (CFU) recovered.
Chromosomal mutants of strain 19660 were generated by allelic exhange. Corneas of C57BL/6 mice were scarified with three parallel 1-mm–long abrasions using a 26-gauge needle and a 2.5-μl aliquot containing ∼1 × 105 bacteria was applied to the scarified cornea. Corneas were imaged at 24hrs and 48hrs for corneal opacity. At 48hrs post infection, whole eyes were homogenized under sterile conditions, serial log dilutions were performed, and bacteria were plated for colony-forming units (CFU). One-way ANOVA was used for statistical analysis.
Deletion of only exoU from strain 19660 still resulted in a highly virulent strain, however; deletion of the entire genomic island encoding exoU reduced virulence significantly. Deletion of genes in the exb28-32 locus of the exoU genomic island did not ameliorate the virulence of strain 19660 as noted by corneal opacity images and CFU counts. However, deletion of exb36, exb39, and exb41 resulted in decreased virulence of strain 19660 and therefore less severe corneal keratitis.
exoU island is responsible for greater virulence of strain 19660. Genes encoding for a nitric oxide reductase, ECF sigma factor, or putative coproporphyrinogen III oxidase are not the virulent factors required for increased virulence. It is the genes located in the exb35-41 locus that are critical for enhanced virulence of strain 19660.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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