SYDNEY – Scientists in Australia's tropical north are collecting blood from crocodiles in the hope of developing a powerful antibiotic for humans, after tests showed that the reptile's immune system kills the HIV virus.

The crocodile's immune system is much more powerful than that of humans, preventing life-threatening infections after savage territorial fights which often leave the animals with gaping wounds and missing limbs.

"They tear limbs off each other and despite the fact that they live in this environment with all these microbes, they heal up very rapidly and normally, almost always without infection," said Mark Merchant, an American scientist who has been taking crocodile blood samples in the Northern Territory.

Initial studies of the crocodile immune system in 1998 found that several proteins (antibodies) in the reptile's blood killed bacteria that were resistant to penicillin, such as Staphylococcus aureus or golden staph, Australian scientist Adam Britton told Reuters on Tuesday. It was also a more powerful killer of the HIV virus than the human immune system.

"If you take a test tube of HIV and add crocodile serum it will have a greater effect than human serum. It can kill a much greater number of HIV viral organisms," Britton said from Darwin's Crocodylus Park, a tourism park and research center.

Britton said the crocodile immune system worked differently from the human system by directly attacking bacteria immediately an infection occurred in the body.

"The crocodile has an immune system which attaches to bacteria and tears it apart and it explodes. It's like putting a gun to the head of the bacteria and pulling the trigger," he said.

For the past 10 days Britton and Merchant have been carefully collecting blood from wild and captive crocodiles, both saltwater and freshwater species. After capturing a crocodile and strapping its powerful jaws closed the scientists extract blood from a large vein behind the head.

"It's called a sinus, right behind the head, and it's very easy just to put a needle in the back of the neck and hit this sinus and then you can take a large volume of blood very simply," said Britton.

The scientists hope to collect enough crocodile blood to isolate the powerful antibodies and eventually develop an antibiotic for use by humans.

"We may be able to have antibiotics that you take orally," Merchant said. " Potentially also antibiotics that you could run topically on wounds, say diabetic ulcer wounds. Burn patients often have their skin infected and things like that."

However, the crocodile's immune system may be too powerful for humans and may need to be synthesized for human consumption.

"There is a lot of work to be done," Britton said. "It may take years before we can get to the stage where we have something to market."