Abstract
Abstract: :
Purpose: To analyze the contribution of swarming to the course and severity of experimental Bacillus endophthalmitis. Methods: The pathogenesis of B. cereus strains NCIB 8122 (wild type, swarmer) and a non–swarming mutant (MP01) were compared in the experimental rabbit endophthalmitis model. Rabbit eyes were injected intravitreally with 2 log10 CFU of NCIB 8122 or MP01. Pathogenicity was compared throughout the course of infection by biomicroscopy, histology, electroretinography, and bacterial quantitation. Phenotypic assays were used to compare the toxin and motility profiles of each strain. Results: Wild type and non–swarming B. cereus grew at comparable rates in vitro. Both strains exhibited the following toxic activities: phosphatidylinositol–specific and phosphatidylcholine–specific phospholipases C, sphingomyelinase, cereolysin O, hemolysin IV, and protease. The primary phenotypic difference in these strains was the inability of MP01 to swarm on solid agar. In the experimental endophthalmitis model, both strains grew to similar numbers in the vitreous throughout the course of infection. However, the non–swarming mutant did not migrate to the anterior segment during infection. The rate of decrease in retinal responses of eyes infected with the non–swarming mutant was similar to that of wild type, with both strains resulting in near complete elimination of retinal function by 12 h. Both strains also caused significant increases in implicit times of retinal responses. In terms of posterior segment inflammation and retinal destruction, outcomes were similar with each strain. However, fibrin and cellular accumulation in the anterior chamber, hyphema, and corneal ring abscesses were not observed in eyes infected with the non–swarming mutant. Conclusions: In this model, a deficiency in swarming prevented Bacillus from migrating to the anterior segment, leading to less severe anterior segment pathology. However, the deficiency in swarming had little effect on retinal function loss, or the overall course or severity of experimental Bacillus endophthalmitis.
Keywords: bacterial disease • endophthalmitis • retina