Abstract
Purpose :
During Staphylococcus aureus endophthalmitis, neutrophils infiltrate into the eye but do not clear the infection. Leukotoxins help S. aureus evade an immune response by lysing neutrophils. We reported that the most common leukotoxin in clinical ocular isolates was LukED. Here, we tested the hypothesis that LukED contributes to the pathogenesis of S. aureus endophthalmitis.
Methods :
LukED expression in brain heart infusion (BHI), tryptic soy broth, and explanted vitreous was compared using qRT-PCR of mRNA purified from S. aureus JE2 cultured in the three environments. In vitro growth of JE2 and its isogenic LukE mutant (JE2ΔlukE) was compared by track diluting colony-forming units (CFU)/mL every 2 h for 18 h. Endophthalmitis initiated by JE2 or JE2ΔlukE was also compared. C57BL/6J mice were intravitreally injected with 5000 CFU of JE2 or JE2ΔlukE. At 6, 12, and 24 h postinfection, eyes were harvested, homogenized, and track diluted to quantify intraocular growth. Inflammation was semi-quantified by myeloperoxidase (MPO) ELISA. Eyes were also analyzed by histology.
Results :
The expression of LukED subunits in S. aureus JE2 were similar in vitreous compared to expression in laboratory media. JE2 and JE2ΔlukE grew to similar concentrations in BHI at all time points, reaching stationary phase at 8 h. The growth rates of JE2 and JE2ΔlukE during the exponential phase were 3.78 h-1 and 3.85 h-1 respectively. In vivo, growth differences were observed, where the growth rates from 0-6 h for JE2 and JE2ΔlukE were 1.19 h-1 and 0.68 h-1, respectively. At 12 and 24 h, growth rates of JE2 and JE2ΔlukE were similar. At 12 and 24 h, growth rates for JE2 were 0.47 h-1 and 0.22 h-1. Growth rates for JE2ΔlukE at the same time points were 0.46 h-1 and 0.38 h-1. MPO/eye in JE2 and JE2ΔlukE infected eyes were comparable at all time points. Histology showed evolving damage to retinal architecture and inflammation over time, which was similar in eyes infected with JE2 and JE2ΔlukE.
Conclusions :
LukED subunits were detected in explanted vitreous, suggesting that this toxin may be expressed in the ocular environment. Given that the in vivo growth and intraocular inflammation caused by JE2 and its LukED-deficient mutant were similar, LukED may not contribute significantly to staphylococcal endophthalmitis pathogenesis. Functional redundancies of other leukotoxins and their contributions to endophthalmitis have yet to be determined.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.