Methicillin resistance in Staphylococcus aureus modulates the transcriptome and disease pathology in a murine model of endophthalmitis

The ever-increasing incidence of methicillin-resistant strains of Staphylococcus aureus (MRSA) endophthalmitis is of particular concern as they are associated with poor outcomes. To compare the histology and whole transcriptome of Methicillin resistant (MRSA) and Methicillin-susceptible (MSSA) Staphylococcus aureus endophthalmitis in an experimental murine model. MRSA and MSSA endophthalmitis was induced in C57BL/6 mice and disease progression was scored clinically and histologically at 24 h p.i. Retinal changes were monitored by H&E, CD45, MPO and GFAP staining followed by retinal cell death evaluation. Whole Transcriptome was analysed using the SuperPrint G3 Mouse Gene Expression v2 chip. Differential gene expression analysis (Limma package, R) was done followed by enrichment of pathways (KEGG database). Increased corneal haze, diminished vitreous clarity and red reflex was observed in MRSA infected mice eye compared to MSSA (p = 0.04). Histological assessment also corroborated with increased disease severity in MRSA (p = 0.02). Although MRSA infected eye displayed higher CD45+ cells and greater GFAP intensity, the difference was not statistically significant. However, higher retinal cell death was found to be associated with the MRSA infection (p = 0.007). Our study also revealed that MRSA infection induces changes in host transcriptome (FC = 1.5, p = 0.05), revealing the involvement of several interleukins (IL-11,15,10,1ra), chemokines (CCL-11, CXCL-1), Interferon receptors, GM-CSF, M-CSF, MMPs, Neruopilin2 (NRP-2), Ubiquitin associated peptidase and apoptotic ligands. ErbB signalling, JAK-STAT, adipocytokine and Ras signalling were the top divergently enriched pathways. Our study confirms the differential host immune response triggered by MRSA infection in the eye. Our study may help to elucidate the mechanisms of pathogenesis and to identify additional candidate drug targets for the treatment of MRSA endophthalmitis.