The superbug that munches medicine

A "superbug" which feeds off the antibiotic used to kill it has been found in two patients at a London hospital, The Lancet medical journal reports tomorrow.

In a matter of days, the bacterium enterococcus faecium, a common species found in the gut, managed not only to develop resistance to the antibiotic vancomycin but also mutated so that a strain became dependent on the drug for its survival.

Doctors at St George's Hospital in London admitted a 60-year-old man with a ruptured oesophagus in February 1996. After an operation he developed an infection. One of the causes of his infection was found to be E. faecium and he was treated with antibiotics, but became feverish again after another operation. E. faecium which had been susceptible to the antibiotic vancomycin was now resistant to it and a strain of the bug was found to actually require vancomycin for its growth. The patient was treated with alternative antibiotics and made a full recovery

In the same month, a 64-year-old retired nurse was admitted to the same hospital for a routine operation. He developed an infection afterwards, and vancomycin-resistant and vancomycin-dependent strains of E faecium were isolated. He too eventually recovered.

Resistance to antibiotics is becoming increasingly common, as the World Health Organisation warned earlier this year. Scientists have called for stricter controls over administering antibiotics as the lifespan of drugs shortens all the time.

But it is extremely rare for bacteria to be able to go through such a huge evolutionary change in such a short space of time.

"It is absolutely fascinating the way it takes such evolutionary steps. It would take man 10 million years to achieve such a change," said Dr Ian Eltringham, a clinical microbiologist at Tooting Public Health Laboratory in London.

"The kill becomes the cure for the bug. The ultimate step in the evolution of resistance is when an organism only grows in the presence of an antibiotic ... Have we at last witnessed the emergence of a true superbug?" But he stressed that there was no major public health concern. Vancomycin can only be administered through the veins and is only used in intensive care and specialist units. "As soon as the vancomycin is stopped the bug disappears," said Dr Eltringham. "Doctors need to increase surveillance of the situation and there should be a raised level of awareness but if I see another case in my career I would be honoured."