(FORTUNE Magazine) – Montreal Founded 1997

To see poetic justice visited on your enemies, get an electron microscope: The bacteria that infect us are constantly clobbered by their own infectious germs--viruses called bacteriophages. "Phages" have long been used in Russia as human antibiotics, but elsewhere the idea of unleashing active viruses in patients hasn't caught on.

PhageTech plans to change that. Its founding scientists, from McGill University, are developing conventional drugs that mimic phages' antibacterial effects. The company analyzed how phages subvert their hosts' molecular machinery, then identified key bacterial molecules to target with drugs--the same points of vulnerability that phages zero in on.

Recently the firm reported that it had discovered several phage-mimicking compounds that seriously inhibit growth of Staphylococcus aureus, potentially deadly bacteria that are increasingly resistant to standard antibiotics. The company has eight bacterial Achilles' heels in its sights. PhageTech won't be ready to market drugs anytime soon. But its favorite phages have proved once again what every flu victim can attest to--viruses really know how to hit where it hurts. --D.S.