TORONTO - Deep inside a cave in New Mexico, researchers have made a remarkable discovery — bacteria that are resistant to antibiotics, even though they have been pristinely isolated from human contact for more than four million years.

Bacterial resistance to antibiotics — the infection-killing wonder drugs that began with mass-produced penicillin in the early 1940s — was long thought to have arisen because of wholesale and indiscriminate use of the medications to treat and prevent disease in both people and animals.

Over time, more and more disease-causing bacteria have become immune to most antibiotics now in use, including the superbug MRSA. And the growing number of bugs mutating to dodge the killing effects of the drugs has researchers and pharmaceutical companies scrambling to find new agents.

But the discovery of strains of naturally resistant bacteria in the Lechuguilla Cave in Carlsbad Cavern National Park represents a major leap in the understanding of resistance threatening the treatment of infectious diseases around the world.

The conclusion: it isn't just manmade.

"Our study shows that antibiotic resistance is hard-wired into bacteria. It could be billions of years old, but we have only been trying to understand it for the last 70 years," said co-principal investigator Gerry Wright, scientific director of Institute for Infectious Disease Research at McMaster University in Hamilton.

"This has important clinical implications," Wright said. "It suggests that there are far more antibiotics in the environment that could be found and used to treat currently untreatable infections."

That's because a particular bacterium creates its own antibiotic as a means of fighting off other bacteria, said co-author Hazel Barton, a cave microbiologist at the University of Akron who helped recover the micro-organisms within the New Mexico cave.

One way to think of it is the bacterial version of the "Hunger Games" — kill or be killed.

"They're carrying out germ warfare, so it's like an arms race," said Barton, explaining that the bacteria are competing for scarce food resources in their environment, whether in backyard soil or deep within a cavern.

"These chemical weapons that they make are antibiotics," she said Wednesday from Akron, Ohio.

"So these organisms have adapted by developing resistance to those chemical weapons. So even though somebody comes along and spits this weapon at them, they can defend themselves and that's where resistance comes from."

While most of us think of antibiotics as pills from a bottle, most in fact originated in nature, like the mould identified by Briton Alexander Fleming in 1928 that gave rise to penicillin.

"If you look at it in the soil, you've got one bacterium next to another bacterium," Barton said. "That bacterium is squirting out the same drug that you have in that pill."

The Lechuguilla Cave seemed an ideal place to seek bacteria that could not have developed resistance to antibiotics through human or other environmental contact with the drugs.

Discovered in 1986, access to the more than 200-kilometre-long cave has been limited to a few expert cavers and researchers each year. It is also surrounded by an impermeable layer of rock, meaning infiltration of water into the cave can take up to 10,000 years to reach its deepest recesses, an age well beyond the discovery of antibiotics.

The researchers sampled bacteria from so far into the cave — involving a laborious hike of about seven kilometres — that Barton and other researchers had to camp inside its depths during the collection process.

In never-before-visited recesses, they collected strains of bacteria, scraping them off the surfaces of rock. An analysis showed none are capable of causing human disease, but almost all are resistant to at least one antibiotic, with some able to fend off up to 14 of the drugs.

In all, resistance was found to virtually every antibiotic that doctors currently use to treat patients, say the researchers, whose work is published in this week's edition of the journal PLoS One.

The good news is that where there is resistance among bacteria in the environment, there must also be natural antibiotics that other micro-organisms have created.

"What it means is that there's also a broad range of antibiotics we've yet to discover," said Barton, noting that the researchers have already isolated one and are working with a pharmaceutical company to develop it into a drug.

"So we're just hunting them down now."

Naowarat Cheeptham, a cave microbiologist at Thompson Rivers University in Kamloops, B.C., said the implications of the study are "really significant."

"With this study, it has re-emphasized the importance that, you know what, maybe it's already there ... Maybe they already exist in the environment," she said of drug-resistant bacteria and as yet undiscovered antibiotics.

Cheeptham, who was not involved with this research, is also searching for new antibiotic agents in a number of B.C. caverns, including the Helmcken Falls Cave in B.C.'s Wells Gray Provincial Park.

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