Abstract
Purpose:
Phage endolysins are peptidoglycan hydrolases that are produced at the end of phage lytic cycle to digest host bacterial cell wall, facilitating the release of mature phage progeny. The aim of this study is to determine the antimicrobial activity of chimeric phage lysins against clinical isolates of Staphylococcus aureus and to test their therapeutic efficacy in a mouse model of S. aureus endophthalmitis.
Methods:
Chimeric fusion proteins containing multiple catalytic domains and cell wall binding domains were genetically engineered. Their activity against 19 clinical isolates of S. aureus from cases of endophthalmitis was tested using three functional assays (plate lysis, turbidity reduction and MIC determination). Their ability to disrupt biofilm formation was also tested. To determine the therapeutic potential in vivo, a chimeric Ply187 endolysin was injected intravitreally in C57BL/6 mouse eyes at 6 h and 12 h post S. aureus infection. Eyes were examined clinically and subjected to quantitation of viable bacteria, retinal function, inflammatory cytokine levels as well as histological analysis.
Results:
All the chimeric lysins showed strong antimicrobial activity against clinical isolates as well as USA 300 and RN6390, a strain used in the mouse model. A chimeric fusion protein of the Ply187 endopeptidase domain and LysK SH3b cell wall binding domain showed strongest anti-staphylococcal activity as evidenced by complete inhibition of bacterial growth, turbidity reduction and biofilm disruption. Intravitreal injection of Ply187 (both at 6 and 12h post infection) significantly improved the outcome of S. aureus endophthalmitis, preserved retinal structural integrity, and maintained visual function as assessed by ERG analysis. Furthermore, phage lysin treatment dramatically reduced bacterial burden and inflammatory cytokines in the eyes.
Conclusions:
Considering an increased antibiotic resistance among ocular isolates of S. aureus, our study suggests that the phage lysins could be used as potential therapeutic agents for management of bacterial endophthalmitis. Moreover, genetic engineering approaches can be used to generate potent chimeric lysins containing multiple lytic domains to avoid resistance development.
Keywords: 513 endophthalmitis •
720 Staphylococcus •
688 retina