Plastic surgery patients have carried a new class of superbugs resistant to almost all antibiotics from South Asia to Britain and they could spread worldwide, researchers reported Wednesday.

Many hospital infections that were already difficult to treat have become even more impervious to drugs thanks to a recently discovered gene that can jump across different species of bacteria.

This so-called NDM-1 gene was first identified last year by Cardiff University's Timothy Walsh in two types of bacteria, Klebsiella pneumoniae and Escherichia coli, in a Swedish patient admitted to hospital in India.

Worryingly, the new NDM-1 bacteria are resistant even to carbapenems, a group of antibiotics often reserved as a last resort for emergency treatment for multi-drug resistant bugs.

In the new study, led by Walsh and Madras University's Karthikeyan Kumarasamy, researchers set out to determine how common the NDM-1 producing bacteria were in South Asia and Britain, where several cases had turned up.

Checking hospital patients with suspect symptoms, they found 44 cases, 1.5 percent of those screened, in Chennai, and 26 (eight percent) in Haryana, both in India.

They likewise found the superbug in Bangladesh and Pakistan, as well 37 cases in Britain, where several patients had recently travelled to India or Pakistan for cosmetic surgery.

"India also provides cosmetic surgery for other Europeans and Americans, and it is likely that NDM-1 will spread worldwide," said the study, published in the British medical journal The Lancet.

NDM-1 was mostly found in E. coli, a common source of community-acquired urinary tract infections, and K. pneumoniae, and was impervious to all antibiotics except two, tigecycline and colistin.

In some cases, even these drugs did not beat back the infection.

Crucially, the NDM-1 gene was found on DNA structures, called plasmids, that can be easily copied and transferred between bacteria, giving the bug "an alarming potential to spread and diversify," the authors said.

"Unprecedented air travel and migration allow bacterial plasmids and clones to be transported rapidly between countries and continents," mostly undetected, they said.

The emergence of these new drug-resistant strains could become a serious global public health problem as the major threat shifts toward a broad class of bacteria -- including those armed with the NDM-1 gene -- known as "Gram-negative", the researchers warn.

"There are few new anti-Gram-negative antibiotics in development, and none that are effective against NDM-1," the study said.

NDM-1 stands for New Delhi metallo-beta-lactamase-1.

Johann Pitout from the University of Calgary in Canada said patients who have medical procedures in India should be screened for multi-resistant bacteria before they receive care in their home country.