The enzyme was isolated from a virus that attacks bacterial cells.
"Essentially, it cracks them open and releases all the cell contents, so the bacterial cell explodes," said Raymond Schuch of The Rockefeller University in New York, co-author of a study published Thursday in the journal Nature.
Ordinary anthrax responds to antibiotics, but there is concern that terrorists might develop resistant strains. The researchers suggested it would be difficult to create strains that resist the enzyme because it acts on a vital part of the bacterial wall, one that can't easily be modified.
Schuch and colleagues reported that the enzyme, called PlyG lysin, kills anthrax bacteria in the laboratory. What's more, when they infected mice with a related kind of bacteria that can kill the animals within five hours, prompt treatment with PlyG saved 13 of 19 animals.
They also found that spores of this anthrax-related bacteria could be quickly detected using PlyG and a hand-held device.
"I think this is a very clever piece of work," said Stephen Morse, a Columbia University molecular biologist and former program manager of the advanced diagnostics program at the Defense Advanced Research Projects Agency.
The PlyG enzyme possibly could be made into a drug that would hunt down anthrax bacteria as they begin to infect a person or an animal, Morse said.
"As always, it will take some time to fully develop and validate this approach to make sure it has therapeutic value, but it's very promising," Morse said.
Phil Hanna, a University of Michigan microbiologist who specializes in anthrax, said the next step will be further animal tests to see if the enzyme can halt an anthrax infection.
The key, Hanna said, as with conventional antibiotics used against anthrax is early treatment before the bacteria produce enough toxin to kill healthy cells and tissue.
"If you wait too long, until serious symptoms appear, even if you use antibiotics to kill all the anthrax bacteria, the animal is doomed because of the toxin levels," Hanna said.
Calvin Chue of the John Hopkins Center for Civilian Biodefense Studies in Baltimore, Md., said the enzyme likely will have more value as an alternative treatment for anthrax than for detecting anthrax bacteria.
"There are detection methods coming down the line that are more useful," Chue said, including equipment that can identify bacterial DNA.