Komodo dragons (Varanus komodoensis) are able to feed on large prey items by injecting a dose of toxic bacteria with their bite that, over time, kills the prey by systemic infection. Dragons also suffer bites from other members of their own species during territorial disputes and feeding frenzies. However, they do not suffer the same fate as their prey, suggesting that they have developed a strong immunity to bacterial infections. This study was undertaken to determine the antibacterial activities of serum from the Komodo dragon. Bacterial cultures were treated with different volumes serum from Varanus komodoensis and the growth was monitored by optical density at 430 nm. In addition, the serum was treated with protease, chelators of divalent metal ions, or with mild heat to determine the mechanism of antibacterial activities. Treatment of bacterial cultures with serum from Komodo dragons (Varanus komodoensis) resulted in a volume-dependent decrease in bacterial growth. Cultures of Escherichia coli, Staphylococcus aureus, and Klebsiella oxytoca exhibited moderate-strong growth inhibition by V. komodoensis serum, while cultures of Streptococcus epidermitis, Salmonella typhimurium, Providencia stuartii, and Shigella flexneri were nearly completely obliterated for 24 h by only 10% (v/v) serum. The antibacterial activity of V. komodensis serum occurred very rapidly, as 18% of E. coli growth was inhibited by a five min exposure to serum. Furthermore, 10- and 20-min incubations of E. coli with serum from V. komodoensis resulted in 43 and 68% inhibition of bacterial growth, respectively. The bactericidal capacity of the serum against E. coli was 2,075,000 bacteria/μL serum, and was inhibited by mild heat treatment, pronase, EDTA, and phosphate, indicating that the anti-bacterial action is most probably due to the presence of a potent serum complement protein system.
innate immunity, lizard, reptile, serum complement, varanid