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Relationship of plcR-regulated factors to Bacillus endophthalmitis virulence
Michelle C Callegan1, Scott T Kane, D Clay Cochran
1Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City 73104, USA. michellecallegan@ouhsc.edu
Abstract:
The explosive, destructive course of Bacillus endophthalmitis has been attributed to the production of toxins during infection. In this study we analyzed the contribution of toxins controlled by the global regulator plcR to the pathogenesis of experimental Bacillus endophthalmitis. Isogenic plcR-deficient mutants of Bacillus cereus and Bacillus thuringiensis were constructed by insertional inactivation of plcR by the kanamycin resistance cassette, aphA3. Rabbit eyes were injected intravitreally with approximately 100 CFU of wild-type B. cereus or B. thuringiensis or a plcR-deficient mutant. The evolution of endophthalmitis resulting from each plcR-deficient mutant was considerably slower than that caused by each wild-type strain. Retinal function was not eliminated until 42 h postinfection in rabbits with endophthalmitis caused by the plcR-deficient mutants, whereas wild-type infections resulted in a complete loss of retinal function within 18 h. The intraocular inflammatory cell influx and retinal destruction in plcR-deficient endophthalmitis approached the severity observed in wild-ype infections, but not until 36 h postinfection. Gross and histological examinations of eyes infected with plcR mutants demonstrated that the anterior and posterior segment changes were muted compared to the changes observed in eyes infected with the wild types. The loss of plcR-regulated factors significantly attenuated the severity of Bacillus endophthalmitis. The results therefore suggest that plcR may represent a target for which adjunct therapies could be designed for the prevention of blindness during Bacillus endophthalmitis.
Insights
The global regulator plcR significantly impacts Bacillus endophthalmitis severity. Disabling plcR in Bacillus cereus and Bacillus thuringiensis reduces eye inflammation and damage, suggesting plcR as a therapeutic target for preventing blindness.
Area of Science:
- Ophthalmology
- Microbiology
- Infectious Diseases
Background:
- Bacillus endophthalmitis is a severe ocular infection characterized by rapid destruction.
- Toxin production by Bacillus species is a key factor in disease pathogenesis.
- The global regulator plcR controls virulence factors in Bacillus.
Purpose of the Study:
- To investigate the role of plcR-regulated toxins in the pathogenesis of experimental Bacillus endophthalmitis.
- To determine if plcR is a viable target for therapeutic intervention.
Main Methods:
- Construction of isogenic plcR-deficient mutants of Bacillus cereus and Bacillus thuringiensis using insertional inactivation.
- Intravitreal injection of wild-type or plcR-deficient strains into rabbit eyes.
- Monitoring of endophthalmitis progression, retinal function, intraocular inflammation, and histological changes.
Main Results:
- plcR-deficient mutants caused a significantly slower progression of endophthalmitis compared to wild-type strains.
- Complete loss of retinal function occurred within 18 h with wild-type infections versus 42 h with plcR-deficient infections.
- Inflammatory cell influx and retinal destruction were attenuated, and anterior/posterior segment changes were less severe in eyes infected with plcR mutants.
Conclusions:
- The global regulator plcR plays a critical role in the severity of Bacillus endophthalmitis.
- Loss of plcR-regulated factors significantly attenuates disease progression and ocular damage.
- Targeting plcR may offer a novel therapeutic strategy for preventing blindness in Bacillus endophthalmitis.