A compound produced by a simple soil microbe may prove a new and extremely effective antibiotic. In recent decades, strains of Staphylococcus aureus and various Enterococcus bacteria have shown resistance to the most powerful antibiotics in the modern medical arsenal. The new compound has wiped out the two superbugs in vitro and in mice.

Jun Wang of Merck Research Laboratories and his colleagues tested 250,000 compounds extracted from microorganisms for antibiotic properties. Platensimycin, isolated from a strain of Streptomyces platensis found in a soil sample from South Africa, showed both strength and discretion in biochemical assays, targeting and defeating pathogens while seeming to show little danger of unwanted interactions. So the researchers tested it against superbugs in vitro. The compound bested methicillin-resistant S. aureus and vancomycin-resistant enterococci as well as other antibiotic-resistant microbes. It also showed no toxicity when put in contact with mammalian cells. Wang and his colleagues then tested the compound in mice infected with S. aureus. After 24 hours of treatment, the compound reduced the bacterial outbreak at least 10,000-fold and showed no deleterious effects on the mice themselves.

Their subsequent research shows that platensimycin works by inhibiting a pathogen's ability to synthesize fatty acids--the essential components of cell membranes. The new antibiotic inserts itself into the nascent chain of a fatty acid and blocks further lengthening, destroying the bacterium's ability to thrive.

"The path ahead remains a long one that includes further preclinical study, and, if these studies are successful, extensive clinical trials for safety and efficacy in humans," writes Eric Brown of McMaster University in Ontario in a commentary accompanying the piece in today's Nature. If it passes all of those tests, platensimycin could be the third new antibiotic--and the strongest--to reach patients in the last 40 years.