Bacteria are developing resistance to current drugs

The researchers, from the drug company Merck, isolated platensimycin from a sample of South African soil.

If the compound passes clinical trials it will become only the third entirely new antibiotic developed in the last four decades.

Details in the journal Nature reveal the antibiotic works in a completely different way to all others.

We very much need new drugs in the pipeline as soon as we can

Professor Tony Maxwell

Most classes of antibiotic were discovered in the 1940s and 1950s, and work by blocking synthesis of the cell wall, DNA and proteins within bacteria.

Most of today's antibiotics are simply tweaks of this basic format.

The fact that they work in similar ways may be one reason why bacteria are proving so adept at developing resistance.

Thus a new class of antibiotics with a different method of action could represent a major breakthrough.

Natural extracts

The researchers hit upon platensimycin during a project in which they screened 250,000 natural product extracts for their antibiotic potential.

It is produced by a strain of the bacteria Streptomyces platensis.

In lab tests, the antibiotic cleared mice of infection with a form of bacteria related to MRSA and did not appear to cause toxic side effects.

Further testing showed activity against a variety of drug-resistant organisms, including MRSA.

Professor Tony Maxwell, who is carrying out similar work at the John Innes Centre (JIC) at Colney in Norfolk, UK, said: "This sounds very promising.

"A number of big pharmaceutical firms have pulled out of antibiotic drug discovery.

"With MRSA cases increasing, and the number of new drugs on the market decreasing, we very much need new drugs in the pipeline as soon as we can."

Alan Johnson, an expert at the Health Protection Agency, said: "There is an increasing problem with antibiotic resistance.

"The Agency welcomes the news that a new antibiotic has been identified that could help to treat infections, particularly those caused by organisms such as MRSA which are resistant to many currently available drugs.

"It should be stressed, however, that the drug is at a very early stage of development and it may be several years before it could be used to treat humans."