Scientists at the University of Washington in Seattle discovered that these bacterium, including the notorious methicillin-resistant Staph aureus, or MRSA, produce lactic acid that counteracts the environment the body produces to prevent most bacteria from growing.

The study, published in Science, focused on nitric oxide -- a chemical the body produces to create an environment noxious to most bacteria. The nitric oxide acts as a natural antibiotic and is excreted by human cells, especially in the nose, that usually keeps microbes from undergoing respiration or fermentation. However, the ability of Staph aureus to produce lactic acid in the presence of nitric oxide keeps the Staph growing.

When Staph aureus was modified and lost its ability to make lactic acid, it could no longer tolerate nitric oxide. The modified bacteria also lost their ability to survive in host immune cells and no longer caused lethal disease in mice.

"MRSA has become an enormous public health problem," study lead author Dr. Ferric Fang said in a statement. "Staph aureus has already colonized about one-third of the world's population, so traditional antibiotics will probably not be the complete answer to the MRSA problem."