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Contribution of membrane-damaging toxins to Bacillus endophthalmitis pathogenesis
Michelle C Callegan1, Daniel C Cochran, Scott T Kane
1Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA. michelle-callegan@ouhsc.edu
Abstract:
Membrane-damaging toxins are thought to be responsible for the explosive clinical course of Bacillus endophthalmitis. This study analyzed the contribution of phosphatidylinositol-specific phospholipase C (PI-PLC) and phosphatidylcholine-specific phospholipase C (PC-PLC) to the pathogenesis of experimental Bacillus endophthalmitis. Isogenic mutants were constructed by insertion of lacZ into Bacillus thuringiensis genes encoding PI-PLC (plcA) and PC-PLC (plcB). Rabbit eyes were injected intravitreally with 2 log(10) CFU of strain BT407 (wild type), the PI-PLC mutant (BTplcA::lacZ), or the PC-PLC mutant (BTplcB::lacZ). The rates of decrease in retinal responses of eyes infected with the isogenic mutants were similar to that of wild type, with all infections resulting in elimination of retinal function by 18 h. Strain BT407 caused a significant increase in the latency of retinal responses at 6 h, but strains BTplcA::lacZ and BTplcB::lacZ did not. All strains elicited significant inflammatory cell influx into the anterior chamber by 12 h. Histologically, eyes infected with each strain were indistinguishable throughout the infection course. In this model, neither PI-PLC nor PC-PLC had an effect on the course or severity of experimental Bacillus endophthalmitis. Alterations in retinal responses early in infection may mark the beginnings of specific photoreceptor or glial cell dysfunction.
Insights
Neither phosphatidylinositol-specific phospholipase C (PI-PLC) nor phosphatidylcholine-specific phospholipase C (PC-PLC) significantly impacted Bacillus endophthalmitis severity in rabbits. Early retinal response changes may indicate photoreceptor or glial cell dysfunction.
Area of Science:
- Ophthalmology
- Microbiology
- Toxicology
Background:
- Bacillus endophthalmitis is characterized by rapid clinical progression, potentially driven by membrane-damaging toxins.
- Phospholipases, including phosphatidylinositol-specific phospholipase C (PI-PLC) and phosphatidylcholine-specific phospholipase C (PC-PLC), are implicated in bacterial pathogenesis.
Purpose of the Study:
- To investigate the specific roles of PI-PLC and PC-PLC in the pathogenesis of experimental Bacillus endophthalmitis.
- To determine if these phospholipases influence disease severity, retinal function, or inflammatory responses.
Main Methods:
- Construction of isogenic Bacillus thuringiensis mutants deficient in PI-PLC (plcA) and PC-PLC (plcB) by lacZ insertion.
- Intravitreal injection of wild-type strain BT407, PI-PLC mutant (BTplcA::lacZ), or PC-PLC mutant (BTplcB::lacZ) into rabbit eyes.
- Assessment of retinal function, inflammatory cell influx, and histological changes throughout the infection course.
Main Results:
- All bacterial strains, including wild-type and phospholipase mutants, led to the elimination of retinal function by 18 hours post-infection.
- While the wild-type strain increased retinal response latency at 6 hours, the PI-PLC and PC-PLC mutants did not show this effect.
- Significant inflammatory cell influx was observed in the anterior chamber for all strains by 12 hours, with no discernible histological differences between groups.
Conclusions:
- In this experimental model, neither PI-PLC nor PC-PLC significantly affected the overall course or severity of Bacillus endophthalmitis.
- Early alterations in retinal responses, observed with the wild-type strain, might indicate initial photoreceptor or glial cell dysfunction independent of these specific phospholipases.