CAVE-DWELLING SUPERBUG OFFERS HOPE
ANCIENT MICROBE MAY HOLD KEY TO LEARNING HOW BACTERIA BECOME DRUG RESISTANT
ANew Mexico cave isolated from the surface for at least 4 million years is home to a superbug resistant to most of the antibiotics mankind has developed to fight disease.
Don’t worry: This bacteria can’t make people sick. In fact, the bug may help scientists find new antibiotics and new strategies for overcoming antibiotic resistance in disease-causing bacteria.
The bacteria lives in Lechuguilla Cave in Carlsbad Caverns National Park. At 1,200 feet below the surface, it is among the deepest limestone caves in the U.S.
“Most of the antibiotics we have now are from soil microorganisms, and we’ve pretty much exhausted that supply,” said Dr. Hazel Barton, a biologist at the University of Akron who is among a handful of researchers allowed to visit the cave.
The superbug, called Paenibacillus LC 231, is one of about 500 species of bacteria that Barton has identified in the cave. She co-authored a study about the bacteria published last month in the journal Nature Communications.
Barton has made about 20 visits to Lechuguilla Cave, which was discovered in 1986 and now is restricted to fewer than 20 scientists and cave experts a year.
No animals have had access to the cave since the entrance collapsed some 50,000 years ago, Barton said.
“It takes about 10,000 years for water to work its way down from the surface,” she said.
Among the most isolated locations on Earth, the cave is an ideal place to study the evolution of bacteria without human influence.
The findings have challenged long-
held assumptions. Scientists once thought that bacteria developed resistance to antibiotics only after people started using them as drugs to fight disease.
Work by Barton and others showed that bacteria produced antibiotics — and had resistance to antibiotics — long before humans were around.
“Antibiotic resistance is ancient and widespread in environmental bacteria,” the study concludes.
In this case, Paenibacillus LC 231 is resistant to 26 of the 40 antibiotics tested in the study.
Researchers sequenced the superbug’s genome and found that it could manufacture 36 antimicrobial compounds, three of which had never been observed before.
“The bacteria didn’t develop resistance, it inherited it,” Barton said. Bacterial genes for producing and resisting antibiotics “are inherited, and they are ancient,” probably dating back billions of years, she said.
Why would bacteria never exposed to humanmade antibiotics have such extraordinary resistance to the drugs?
The answer is found in the difficult conditions for life in Lechuguilla Cave. Nutrients are so scarce in the cave that bacteria derive energy from chemical compounds in the rock.
“This cave is very, very starved,” Barton said. Bacteria “eat the energy in the rock.” Bacteria are pitted against each other for scarce nutrients. “If you have to work that hard to grow, then you don’t want to share your resources.”
Some bacteria, called “social cheaters,” kill other bacteria by “lobbing chemical bombs” at their competitors, she said. We call these toxic bombs antibiotics, and virtually all the antibiotics we have to fight disease are compounds naturally produced by microbes.
But the defending bacteria have their own survival strategies.
“The best way to overcome this cheating is to have a defense,” Barton said. “And the best defense against antibiotics is resistance.”
The severe conditions in Lechuguilla Cave have created the perfect environment to study antibiotics and antibiotic resistance.
“These very isolated, very protected caves will help us to understand some very fundamental questions about antibiotics that we haven’t been able to answer before,” she said.