Gene swap led to superbug

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http://www.abc.net.au/science/news/health/HealthRepublish_999126.htm

 

Gene swap led to superbugAnna Salleh

ABC Science Online

 

Friday, 28 November 2003

 

 

 

 

 

" Golden staph " bacteria can become resistant to the antibiotic of last resort -

vancomycin - by swapping genes with a less aggressive but common species, report

U.S. scientists.

 

Dr Linda Weigel from the Centres for Disease Control and Prevention in Atlanta,

Georgia and colleagues report their findings in today's issue of the journal

Science.

 

The world of antibiotic resistant superbugs is littered with acronyms, like VRE

and MRSA. VRE stands for vancomycin-resistant enterococcus, a common bug found

in hospitals (and in the food supply in Australia and the UK). It's resistant to

the antibiotic that doctors use when all other antibiotics have failed to

control an infection, vancomycin. MRSA stands for methicillin-resistant

Staphylococcus aureus or golden staph, a highly aggressive bug resistant to

everything except vancomycin.

 

In their study, Weigel and team analysed the genetic makeup of an untreatable

infection of Staphylococcus aureus isolated from a Michigan dialysis patient in

June 2002. They found a plasmid (a highly mobile piece of DNA) carrying various

genes for antibiotic resistance. The genes included one called " vanA " ,

responsible for vancomycin resistance in VRE.

 

The crucial vanA gene had jumped into the Staphylococcus aureus, carrying with

it the potential to make the new bug resistant to vancomycin. The jump had

created vancomycin-resistant Staphylococcus aureus, or VRSA.

 

According to Australian infectious diseases expert Dr Peter Collignon, from The

Canberra Hospital, the VRSA discovered in the Michigan patient was a

" microbiologist's nightmare " .

 

" This well done scientific study has shown that, in people, the vanA gene can

jump from a relatively non-aggressive germ like enterococcus into a very

aggressive germ like Staphylococcus aureus, " he told ABC Science Online.

 

He said the fact that so many people infected with VRE were also infected with

MRSA had led to fears the untreatable VRSA superbug would develop. But until now

there had been no evidence that this could actually happen, except in

experimental animals.

 

Japanese scientists had previously found Staphylococcus aureus with a level of

vancomycin resistance lower than VRSA. That resistance turned out not to have a

genetic basis. This is the form of vancomycin resistance that exists in

Staphylococcus aureus in Australia.

 

Dr Michael Whitby is in charge of infection control for Queensland Health in

Australia. He said the research was " another warning " we need to preserve the

effectiveness of existing antibiotics.

 

" Over the past 20 years, vancomyin has been the major agent used to treat

methicillin-resistant Staphylococcus aureus [MRSA]. So if resistance became

widespread in MRSA we would have great difficulty treating that particular

organism, the major antibiotic we use would lose its usefulness, " he said. " Good

infection control in hospitals, controlling the spread of these organisms, is as

important as it ever was. "

 

 

 

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