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New warning on 'superbug'

Genome mapping of S. maltophilia reveals potent drug resistance

James Smith

Wednesday, 07 May 2008

The genome of the newly emerging infection Stenotrophomonas maltophilia has been successfully mapped and the results show a remarkable capacity for drug resistance.

But the Health Protection Agency (HPA) has been quick to play down the risks posed by the “superbug”.

The new research, published in Genome Biology, was carried out by scientists at the Wellcome Trust Sanger Institute and the University of Bristol with the aim of enabling other researchers to discover how to deal with the organism.

Dr Matthew Avison from the University of Bristol, a senior author on the paper, said: “This is the latest in an ever-increasing list of antibiotic-resistant hospital superbugs. The degree of resistance it shows is very worrying.

“Strains are now emerging that are resistant to all available antibiotics, and no new drugs capable of combating these 'pan-resistant' strains are currently in development.”

According to the researchers, S. maltophilia flourishes in moist environments, such as around taps and shower heads, and so can be easily transferred to patients. A typical route of entry for this infection is through catheters that are left in place for long periods of time. The organism is also found in the lungs of many adults with cystic fibrosis, and causes ventilator-associated pneumonias, particularly in elderly intensive-care patients.

While S. maltophilia infections are still relatively uncommon, they are on the increase. Figures from the HPA show that the number of reported cases rose from 613 in 2002 to 773 in 2006, an increase of 26% over four years. The mortality rate is around 30%.

However, a spokesperson from the HPA played down fears of infection: “Stenotrophomonas maltophilia are bacteria which are normally found in soil and ground water. Stenotrophomonas maltophilia infections never affect healthy people and would be most likely to affect those who are already very sick, often in intensive care.

S. maltophilia has always shown resistance to many antibiotics and the study shows some genetic reasons for this. Until recently it had not shown much of a trend that it was becoming more resistant, with the antibiotic co-trimoxazole effective against virtually all strains.

“The infection does not spread in the manner of MRSA or C. difficile; ie. there is little spread between patients, and infections are mostly caused by one-off strains.”  

(Picture: Wellcome Images)

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