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C. Tam, J. J. Mun, D. J. Evans, S. M. J. Fleiszig; Delayed-Onset Pseudomonas Aeruginosa Keratitis in a Rat Contact Lens Model. Invest. Ophthalmol. Vis. Sci. 2008;49(13):831.
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Extended contact lens wear is associated with a higher incidence of bacterial keratitis of the cornea. The underlying causes of the disease are still poorly understood. In this study, we aimed to identify factors that contribute to corneal infection in a rat contact lens model.
The left eyes of female Lewis rats (3 months old) were inoculated with GFP expressing P. aeruginosa strain PA01 (109 cfu in 10 µl). This was done with or without prior blotting with tissue paper (Kimwipes), which disrupts epithelial barrier function (to fluorescein). They were then fitted with low Dk hydrogel contact lenses (custom made to fit the rat eye) that had been pre-soaked in bacteria (1011 cfu/ml) for 2 h. Lenses were not rinsed to remove non-adherent bacteria prior to insertion. The contralateral eyes were untreated as controls. Some rats were allowed to wear the lenses for 2 days before the blotting and bacterial inoculation procedure. Between 1 and 7 days after opacity was first detected the lens was removed from the eye and homogenized for viable bacteria quantification. The eye was then immediately washed with PBS to collect non-adherent bacteria at the ocular surface. Eyes were enucleated and analyzed for immunohistochemistry.
Contact lens wear did not reliably induce infection without blotting, even when the eye was inoculated with bacteria at multiple time points. Blotted eyes wearing contact lenses began to show corneal opacity between 5 and 14 days after the blotting/bacteria inoculation procedure. In most cases this was followed by severe keratitis, but in other cases the opacity did not progress to severe disease even when followed for up to a week. Phagocyte infiltration was found in all corneas showing opacity, but bacteria were found within the cornea only in eyes showing severe disease. In either case, significant numbers of bacteria were detected in the ocular surface wash (~105 cfu total) and on worn contact lenses (~107 cfu total) even after 21 days of wear. Recovered bacteria were found to express GFP verifying that they were derived from the original inoculum added on the first day of the experiment.
Initially, epithelial disruption does not enable infection, even when bacteria are added with contact lens wear. However, bacteria can then survive at the ocular surface after continued contact lens wear to ultimately cause disease within 1-2 weeks. Whether or not the mechanism for infection at this later time point involves adaptation of bacteria to the in vivo environment or effects of long-term lens wear on the cornea is yet to be determined.
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