Frog skin provides crab-friendly alternative for detecting bacteria
By Ben Coxworth
October 21, 2010
Confused by that headline? It's simple really – when drugs and medical devices are tested for contamination, a substance called Limulus amebocyte lysate (LAL) is used. LAL is made from the blood cells of horseshoe crabs, which are caught along the U.S. Atlantic coast, drained of 30 percent of their blood, then returned to the water. Although the majority of the crabs survive the process, it has been estimated that at least 30 percent do not. This, in turn, is affecting populations of the red knot, a bird that feeds on horseshoe crab eggs. Now, engineers from Princeton University have discovered that a substance from the skin of the African clawed frog could be used instead of the crab blood – with no harm done to the frog. No word on whether eye of newt or wing of bat would work, too.
Horseshoe crabs are used because their immune system has evolved to produce amebocytes, antimicrobial blood cells that fight off the bacteria that are plentiful in the crabs’ seabed environment. When a drug or device sample is added to a solution of LAL, which is made from the amebocytes, the solution will turn to gel if the sample is contaminated.
Like the crabs, the frogs also have an antibacterial defense system. They produce peptides (small chains of amino acids) on their skin, to protect against infections. The Princeton engineers have discovered a method of attaching these peptides to a small electronic chip, that emits a signal when exposed to bacteria such as E. coli and salmonella. The African frogs, which are common in laboratories and pet stores, are not harmed in the process, and the peptides can be synthesized.
“It's a robust, simple platform,” said lead researcher Michael McAlpine. “We think these chips could replace the current method of testing medical devices and drugs.”