It’s not just the teeth that are formidable (Image: Jody Watt/Design Pics/Corbis)

Thick armour and jaws packed full of teeth aren’t the only defences that alligators and crocodiles have. They also have formidable immune systems and some of the protective molecules that enable this have now been identified. Their discovery in the blood of the American alligator might even pave the way for a new generation of antibiotics.

Crocodilians have existed on Earth for at least 37 million years. Over the course of their evolution, they have developed a very strong defence against infection. “They inflict wounds on each other from which they frequently recover without complications from infection despite the fact that the environments in which they live are less than sterile,” says Barney Bishop of George Mason University in Fairfax, Virginia, co-author of the new study.

American alligators have an enviable innate immune system, the “primitive” first line of defence that is shared by all vertebrates. In 2008, chemists in Louisiana found that blood serum taken from the reptiles destroyed 23 strains of bacteria and depleted reserves of the HIV virus. The germ-killing molecules were identified as enzymes that break down a type of lipid.


Although their results have yet to lead to any new antibiotics, enzymes aren’t the only pathogen-busting molecules that alligators have up their sleeve. Bishop’s group has now identified and isolated peptides known as a CAMPs or cationic antimicrobial peptides.

Fishing with charges

These molecules are positively charged so the team developed nanoparticles to electrostatically pick them out of the complex mix of proteins in alligator blood plasma.

In total, the group fished out 45 peptides. Of these, they chemically synthesised eight and evaluated their antimicrobial properties. Five killed some of the E.coli bacteria they were presented with, while the other three destroyed most of the E.coli and also showed some activity against bacteria including Pseudomonas aeruginosa, which can cause inflammation and sepsis, and Staphylococcus aureus, which can trigger skin infections, sinusitis and food poisoning. So far, the strains have performed well, says Bishop.

The researchers are now extending their analysis to other members of the crocodilian family including gharials and Siamese crocodiles.

Identifying novel antimicrobial peptides is urgently needed because of the growing problem of antibiotic resistance, says Guangshun Wang at the University of Nebraska Medical Center in Omaha. “Because of the novelty of the sequences,” he says, “these peptides provide new templates for developing antimicrobials to combat superbugs.”

Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0117394