Anti-viral activity of Staphylococcus aureus lysates against herpes simplex virus type-I infection: an in vitro and in vivo study

AIM: To investigate the effect of Staphylococcus aureus (S. aures) lysates (SALs) on herpes simplex virus type-I (HSV1) infection in human corneal epithelial (HCE) cells and in a mouse model of HSV1 keratitis. METHODS: HCE, Vero, HeLa, and BV2 cells were infected with HSV1 [HSV1 f strain, HSV1f; HSV-1-H129 with green fluorescent protein (GFP) knock-in, HSV1g]. Pre- or post-infection, SAL at various concentrations was added to the culture medium for 24h. GFP fluorescence in HSV1g or plaque formation by HSV1f were examined. The effects of heat-treated SAL, precooled acetone-precipitated SAL, and SAL subjected to ultrafiltration (100 kDa) were evaluated. The effects of other bacterial components and lysates on HSV1 infection were also tested, including lipoteichoic acid (LTA), peptidoglycan (PGN), staphylococcal protein A (SPA), and α-hemolysin from S. aureus (α-toxin) as well as lysates from a wild-type S. aureus strain, S. epidermidis, and Escherichia coli (W-SAL, SEL, and ECL, respectively). In addition, SAL eye drops were applied topically to BALB/c mice with HSV1 keratitis, followed by in vivo observations. RESULTS: The cytopathic effect, plaque formation (HSV1f), and GFP expression (HSV1g) in infected cells were inhibited by SAL in a dose-dependent manner. The active component of SAL (≥100 kDa) was heat-sensitive and retained activity after acetone precipitation. In HSV1g-infected cells, treatment with LTA-sa, α-toxin, PGN-sa, or SPA did not inhibit GFP expression. SAL, W-SAL, and SEL (but not ECL) decreased GFP expression. In mice with HSV1 keratitis, SAL reduced corneal lesions by 71%. CONCLUSION: The results of this study demonstrate that SAL can be used to inhibit HSV1 infection, particularly keratitis. Further studies are needed to determine the active components and mechanism underlying the effects of SAL.