Published On January 18, 2017
MICROBES THAT RESIST COMMON ANTIBIOTICS CONTINUE TO RAISE ALARM, taking more than 23,000 lives every year in the United States. The search for novel antibiotics to treat them has long been under way (“The War on Superbugs,” Fall 2008) and has led to faraway places, including the floor of the ocean (“Testing the Waters,” Summer 2015). But one team of investigators has recently discovered a promising new antibacterial candidate literally under their own noses.
A group at the University of Tübingen in Germany was looking for new ways to fight methicillin-resistant Staphylococcus aureus, or MRSA, one of the deadliest and most common superbugs. Roughly 20% of the population harbors the S. aureus bacterium, typically in the armpit, groin or nose. While most of those carriers never suffer consequences, the germ can invade wounds or other entry points and cause serious infections of the skin, bone, blood, heart and lungs. About 2% of people have the more dangerous MRSA strain, which has become endemic in some hospitals and causes the deaths of about 11,000 Americans every year.
The German team wondered why S. aureus only lives in about one third of human noses. Led by senior scientist Bernhard Krismer, they began to investigate how S. aureus competed for resources in this unusual biological niche. “It’s a very nutrient-poor environment,” says Krismer, noting that nasal microbes fight over a small amount of amino acids and glucose for sustenance. “Competition is quite high.”
Krismer and his colleagues took 90 strains of bacteria isolated from nasal secretions and tested them against S. aureus in the lab. Most had no effect, but one strain, S. lugdunensis—which about 9% of humans carry—stopped S. aureus from reproducing in a dish. When the two strains of bacteria were sprayed into the noses of rats, most of the S. aureus disappeared after just five days. The researchers then took nasal swabs from more than 180 hospital patients and determined that those who carried S. lugdunensis were six times less likely to test positive for S. aureus. They published the results of their work in Nature in July 2016.
The team suspected that S. lugdunensis carries some kind of powerful weapon that allows it to defend its territory from other microbes without harming its host. Other microorganisms produce toxins that help them compete for resources—penicillin and vancomycin are in fact distilled from such microbial toxins. But this was perhaps the first such bacterium found inside the human body.
The researchers extracted a compound from S. lugdunensis, which they named lugdunin, and found that it eliminated S. aureus infection from the skin of mice. So far lab testing indicates that S. aureus does not develop resistance to lugdunin. (Drug-resistant mutations are often the result of antibacterials that are not completely effective in killing the target pathogen). Tests indicate that lugdunin destroys other hard-to-treat bacteria as well, including vancomycin-resistant Enterococcus, a common lurker in hospitals that causes urinary and blood infections.
The next step is to develop lugdunin into a drug that could be used as either a topical treatment for skin infections or as a nasal spray that would kill S. aureus before patients undergo surgery. And S. lugdunensis may just be the beginning. Krismer believes that other antibiotic candidates likely await discovery within the human body.
Stay on the frontiers of medicine
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- Testing the Waters
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- The War on Superbugs
As medicine battles antibiotic resistance, tougher drugs breed still more deadly bacteria. New approaches could break the cycle.