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New superbug threat on the horizon

Superbug fear A new antibiotic-resistant superbug already causing problems in hospitals is set to become a whole lot more virulent, say an international team of researchers.

At the same time, they add, virulent strains that are infecting healthy people in some parts of the world are becoming more resistant to antibiotics.

The culprit is Klebsiella pneumoniae, one of the top five bacteria involved in hospital acquired infections, causing pneumonia, wound infections and urinary tract infections.

"Klebsiella pneumoniae is now recognised as an urgent threat to human health because of the emergence of multidrug-resistant strains associated with hospital outbreaks and hypervirulent strains associated with severe community-acquired infections," write researchers in this week's issue of the Proceedings of the National Academy of Sciences.

And, now, they say, virulence and resistance genes in different strains of the bacteria are poised to converge, which could lead to a massive number of serious untreatable infections.

"I would say it's inevitable," says lead author Dr Kathryn Holt from the University of Melbourne.

Genomic analysis

Holt and colleagues sequenced the genomes of 300 different strains of K. pneumoniae from around the world to find genes linked to virulence and drug resistance.

They found that strains virulent enough to infect healthy people in the general population -- mainly in areas of the world with poor sanitation -- had four genes that enabled the bacteria to steal iron from human body cells.

These 'virulence genes', however, were not present in the strains that infect sick people in hospitals.

While the virulent strains are currently readily treatable by antibiotics, the less-virulent strains are causing problems in hospitals because they are resistant to many antibiotics.

Of most concern, is a strain of K. pneumoniae dubbed KPC, which is resistant to the antibiotic carbapenem, and which just last week was linked to deaths in the Australian state of Victoria.

Many more deaths are being blamed on KPC in Greece and Italy, says Holt, a computational biologist specialising in bacterial pathogens.

She says there is already concern that growing drug resistance could make K. pneumoniae a greater problem than MRSA in hospitals.

Fatal combination

The real worry, says Holt, is the mixing of strains containing virulence and antibiotic-resistance genes.

"The antibiotic resistance genes, and these iron acquisition genes that make the bacteria more virulent, are highly mobile so they can spread from one strain to another quite easily," she says.

If that happens, community-based infections caused by virulent strains in places like Asia no longer be treatable by antibiotics. In addition, the antibiotic-resistant strains in hospitals could become more virulent, says Holt.

"So now we're watching and waiting."

Holt says one of the features of K. pneumoniae is that it's more widespread in the environment than any of the other bacteria of concern to humans, and is able to live in soil and on plants.

Together with the fact that it is so good at sharing new genetic material, this means that K. pneumoniae is the perfect "trafficker" of genes from the environment to bacteria such as E. coli, which only live in animal hosts.

The gene that makes the KPC strain so resistant to antibiotics has already spread into E. coli and is starting to cause problems in hospitals, says Holt.

She says the only way forward is to use genomic approaches in hospitals and public health labs to monitor what's happening with the bacteria.

"If we start to see increasing resistance and virulence in a particular hospital or associated with a particular type of surgery, or a particular type of antibiotic, we can try to limit the impact," she says.