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J. J. Hunt, M. C. Callegan; The Role of Klebsiella pneumoniae Capsular Polysaccharide in Experimental Endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6337.
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To evaluate the role of the capsular polysaccaride (CPS) of Klebsiella pneumoniae in experimental endophthalmitis.
C57Bl/6 mice were intravitreally injected with K. pneumoniae strain NTUHK2044 or an isogenic magA-deficient mutant (CPS negative). Bacterial growth was quantified by plating whole eye homogenates. Visual function was assessed by scotopic electroretinography (ERG). Inflammation was measured by myeloperoxidase (MPO) assay and whole eye histology.
Wild type K. pneumoniae grew to a higher density in the eye, reaching 108 CFU/eye, compared to only 105 CFU/eye for the magA mutant. Mice infected with the magA mutant also retained greater visual function. At 24 h, the percent retained A- and B-wave function of eyes infected with the magA mutant were 40-50% higher than that of eyes infected with the wild type strain. ΔmagA-infected eyes showed an upward trend in percent retained function, while wild type eyes continued to lose function between 18 and 24 h. However, equivalent MPO was recovered from eyes regardless of the bacterial strain used, except at 24 h. Histologically, eyes infected with wild type K. pneumoniae showed cellular infiltration, fibrin deposition, and corneal thickening at least 6 h earlier than eyes infected with the magA mutant.
The host immune responsewas better able to control K. pneumoniae when the bacteria did not produce a capsule. These results may indicate that the capsule is anti-inflammatory or that the bacteria are less able to resist killing action of infiltrating PMNs. Future studies will be focused on this distinction.
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