4 mn-year-old cave has drug-resistant microbes

Singapore: Scientists have discovered that several hundred types of bacteria, which thrive on the walls of the Lechuguilla cave system in the state of New Mexico in US, are resistant to modern antibiotic drugs. The cave system exists on rock faces that are located 1,600 feet (487 meters) below Earth's surface and is estimated to have been isolated for the past four-to-seven million years. The study was published in the journal PLoS ONE.

Although the microbes are not infectious to humans, it can resist multiple classes of antibiotics, including synthetic drugs. The discovery serves as an intriguing lead in the quest to understand how drug-resistant diseases emerge.

Dr Wright's team managed to grow 500 different kinds of bacteria from the Lechuguilla caves, but only 93 grew in a medium that allows testing for resistance to 26 different antimicrobial agents. Of those 93, about 70 percent resisted three-to-four classes of antibiotics. Three of these strains, which are distant relatives of the bacterium that creates anthrax spore, appeared to fight off 14 of the 26 antibiotics.

Dr Gerry Wright, study leader and chemical biologist at McMaster University in Ontario, Canada, said that, "Clinical microbiologists have been perplexed for the longest time. When you bring a new antibiotic into the hospital, resistance inevitably appears shortly thereafter, within months to years. It's still a big question: Where is this coming from? Almost no one thought to look at other bacteria, the ones that don't necessarily cause disease."

Lechuguilla is one of the deepest and most extensive cave systems in New Mexico's Carlsbad Caverns National Park. Although the US National Park Service strictly limits entry to the cave, since 2008 it has allowed geomicrobiologist Dr Hazel Barton of Northern Kentucky University and her team in the cave in order to sample its microbial life. Dr Barton scraped off and bagged samples of biofilms growing on the cave walls and delivered them to Dr Wright's laboratory, where his team spent three years probing the samples for any signs of antibiotic resistance.

Many microbiologists suspect that nonpathogenic bacteria are acting as a vast pool of ancient resistance genes waiting to be transferred to pathogenic bacteria. While speaking in this regard, Dr Wright said that, "It's kind of a thesis at this point: These benign environmental organisms are the root of resistance. There are so many of them with so many resistance genes that could move horizontally through populations."

The cave finding builds on Dr Wright's previous work, in which he found bacteria with resistance genes in primordial soils untouched by humans, normal soils, and permafrost. Dr Wright wanted firmer evidence that antibiotic resistance genes are ancient and not a new microbiological fad.