Abstract/Summary

Infections caused by multi-drug-resistant (MDR) bacteria are a global threat to human health. As venoms are the source of biochemically diverse bioactive proteins and peptides, we investigated the antimicrobial activity and murine skin infection model-based wound healing efficacy of a 13 kDa protein. The active component PaTx-II was isolated from the venom of Pseudechis australis (Australian King Brown or Mulga Snake). PaTx-II inhibited the growth of Gram-positive bacteria in vitro, with moderate potency (MICs of 25 µM) observed against S. aureus, E. aerogenes, and P. vulgaris. The antibiotic activity of PaTx-II was associated with disruption of membrane integrity, pore formation and lysis of bacterial cells, as evidenced by scanning and transmission micros-copy. However, these effects were not observed with mammalian cells, and PaTx-II exhibited minimal cytotoxicity (CC50 > 1000 µM) toward skin/lung cells. Antimicrobial efficacy was then determined using a murine model of S. aureus skin infection. Topical application of PaTx-II (0.5 mg/kg) cleared S. aureus with concomitant increased vascularization and re-epithelialization promoting wound healing. As small proteins and peptides can possess immunomodulatory ef-fects to enhance microbial clearance, cytokines and collagen from the wound tissue samples were analyzed by immunoblots and immunoassays. The amounts of type I collagen in PaTx-II treated sites were elevated compared to the vehicle controls, suggesting a potential role for collagen in fa-cilitating the maturation of the dermal matrix during wound healing. Levels of proinflammatory cytokines interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), cy-clooxygenase-2 (COX-2) and interleukin-10 (IL-10), factors known to promote neovasculariza-tion, were substantially reduced by PaTx-II treatment. Further studies that characterize the con-tributions towards efficacy imparted by in vitro antimicrobial and immunomodulatory activity with PaTx-II are warranted.