Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/2/2014
Publication Date: 6/2/2014
Citation: Singh, P.K., Donovan, D.M., Kumar, A. 2014. Intravitreal injection of a chimeric phage endolysin Ply187 protects mice from Staphylococcus aureus endophthalmitis. Antimicrobial Agents and Chemotherapy. 58(8):4621-4629. Interpretive Summary: STET. There is a need for antimicrobial treatments into the eyeball to cure infections of the eye caused by the bacterium, Staphylococcus aureus, especially following cataract surgery. Staphylococcus aureus are notoriously prone to antibiotic resistance development, thus novel antimicrobials that avoid resistance development are much needed. STET. A novel antimicrobial protein derived from a virus that infects bacteria was tested and shown to reduce or eradicate Staphylococcus aureus bacteria infecting the eye ball in a mouse model of eye infection. STET. The identification of a novel antimicrobial agent that is functional in the eye to cure Staphylococcus aureus bacteria infections is the first step required prior to commercialization of such an agent for the eventual use by health care workers worldwide. This finding opens the door to testing many other antimicrobial proteins. This is especially important due to the ‘immune priveledged’ status of the eye, where unlike most other body cavities, immune cells do not invade. Thus there is not expected to be a significant immune response to antimicrobial proteins injected into the eye.
Technical Abstract: Objectives: The treatment of endophthalmitis is becoming very challenging due to the emergence of multidrug-resistant bacteria. Hence, the development of novel therapeutic alternatives for ocular use is essential. Here, we evaluated the therapeutic potential of Ply187AN-KSH3b, a chimeric phage endolysin derived from the Ply187 prophage in a mouse model of Staphylococcus aureus endophthalmitis. Methods: The in vitro antimicrobial activity of the chimeric Ply187 endolysin was assessed by plate lysis, turbidity reduction, and inhibition of biofilm formation assays. For in vivo studies, the endolysin was injected intravitreally in C57BL/6 mouse eyes at 6h and 12h post S. aureus infection. The disease progression was monitored by ophthalmoscopic, electroretinography (ERG), histological, cell death (TUNEL labeling), and microbiological parameters. The expression of cytokines/chemokines was assessed via ELISA. Flowcytometry was used to determine cellular infiltration. Results: The chimeric Ply187endolysin exhibited strong antimicrobial activity against the S. aureus strain RN6390, as evidenced by a complete inhibition of bacterial growth, reduction in turbidity and disruption of biofilms. The intravitreal injection of chimeric Ply187 (both at 6 and 12 h post infection) significantly improved the outcome of staphylococcal endophthalmitis, preserved retinal structural integrity, and maintained visual function as assessed by ERG analysis. Furthermore, phage lysin treatment significantly reduced the bacterial burden and the levels of inflammatory cytokines and neutrophil infiltration in the eyes. Conclusion: These results indicate that the intravitreal administration of a phage lytic enzyme construct attenuates the development of bacterial endophthalmitis in mice. To the best of our knowledge this is the first study demonstrating the therapeutic use of phage-based antimicrobials in ocular infections.