MRSA is resistant to conventional antibiotics

Canadian scientists tested 480 different soil bacteria and found every single one had some resistance to major classes of antibiotics.

The findings, in the journal Science, suggest bacteria have long been skilled at foiling their foes.

They may also explain how resistance is developed so quickly to new drugs.

The soil serves as an under-recognized source of resistance, resistance that has the potential to reach clinics Professor Wright McMaster University

There has been growing concern about drug-defying superbugs, such as MRSA, which doctors are no longer able to treat with traditional antibiotics.

Doctors have been warned to use antibiotics sparingly, as bacteria seem to have an astonishing capacity to neutralise their effect.

Lead researcher Professor Gerry Wright, of McMaster University in Ontario, said his team's work could help understand better how resistance develops - and aid the development of new, more effective drugs.

The researchers focused on soil bacteria called actinomycetes, which are known to produce approximately two-thirds of all known antibiotics.

They tested the bacteria for resistance to 21 commonly-used antibiotics, and analysed their genetic make-up to try to pin down the nature of the resistance.

Every strain was found to be resistant to seven or eight antibiotics on average - and two strains were resistant to 15 out of the 21 drugs.

The researchers found resistance among the soil bacteria to one of the most commonly prescribed antibiotics - vancomycin - was identical to that found in disease-causing bugs in the hospital setting.

They also found evidence of resistance to a new antibiotic drug called telithromycin which was only approved in 2004.

'New avenues'

Professor Wright said: "The link between clinical and soil-associated resistance to vancomycin illustrates the value of studying resistance in the soil to rationally anticipate future clinical resistance.

"It suggests that the soil serves as an under-recognized source of resistance, resistance that has the potential to reach clinics."

Dr Bhagirath Singh, scientific director of the Canadian Institutes of Health Research Institute of Infection and Immunity, said: "Dr Wright's discovery points to the fact that in nature, bugs in the soil survive in a very hostile environment.

"They do this by developing resistance to the antibiotics produced by other soil bacteria.

"Understanding this process opens up a new avenue for finding new therapies to prevent and treat antibiotic resistance in a clinical setting."

Dr Alan Johnson, an expert on antibiotic resistance at the Health Protection Agency, said the study highlighted the importance of studying soil bacteria for clues to how resistance to drugs begins.

"While bacteria causing infections in humans have been exposed to antibiotics for only about 60 years, bacteria in soil will have been exposed to antibiotics for very much longer.