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Hypermucoviscosity as a Virulence Factor in Experimental Klebsiella pneumoniae Endophthalmitis

¹From the Oklahoma Center for Neuroscience and the ²Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center (OUHSC), Oklahoma City, Oklahoma; and the ³Department of Ophthalmology, Dean A. McGee Eye Institute, Oklahoma City, Oklahoma.

PURPOSE. Klebsiella pneumoniae is a common cause of endogenous bacterial endophthalmitis, a disease that frequently results in a poor visual outcome. Hypermucoviscosity has been identified as a virulence factor among clinical bacteremia isolates of K. pneumoniae. In this study, an experimental murine model of K. pneumoniae endophthalmitis was established, and the role of hypermucoviscosity in its pathogenesis was analyzed.

METHODS. C57BL/6J mice were intravitreously injected with 100 CFU of hypermucoviscous (HMV+) or nonhypermucoviscous (HMV–) K. pneumoniae. Intraocular bacterial growth, retinal function, gross pathology, and inflammatory responses were monitored every 3 hours until the eyes lost significant (>90%) retinal function, or the infection appeared to clear.

RESULTS. The HMV+ strain grew logarithmically in eyes until approximately 15 hours postinfection (PI), reaching a stationary phase of growth at approximately 8.0 log₁₀ CFU/eye. The HMV– strain grew logarithmically to approximately 7.6 log₁₀ by 18 hours, but bacterial count declined to approximately 6.4 log₁₀ CFU/eye by 21 hours PI. Eyes infected with the HMV+ strain retained approximately 35% a-wave and <10% b-wave function by 18 hours PI. These eyes also had a cumulative clinical score of 14+ by 18 hours and underwent phthisis between 21 and 24 hours. Eyes infected with the HMV– strain had a cumulative clinical score of <6 and retained >60% a-wave and >50% b-wave function throughout 21 hours. Five of 7 eyes had <100 CFU HMV– K. pneumoniae at 27 hours PI.

CONCLUSIONS. The findings demonstrate the site-threatening consequences of K. pneumoniae endophthalmitis and the importance of the hypermucoviscosity phenotype in the pathogenesis of experimental K. pneumoniae endophthalmitis.

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