Two labs said on Thursday that the DNA of a bacterium behind a lethal E. coli outbreak in Germany pointed to a new strain of microbe whose genetic mix explained its remarkable virulence.

The genetic sequence indicates an "entirely new super-toxic E. coli strain," Chinese lab BGI said, adding that it had also found evidence the microbe was resistant to antibiotics.

BGI said the microbe was a new serotype -- a term meaning a variation in a sub-species of bacterium -- that was "not previously involved" in any Escherichia coli outbreaks.

In a press release issued from Shenzhen, southern China, BGI said it was working with the University Clinic Hamburg-Eppendorf in northern Germany, the epicentre of the outbreak which has claimed 18 lives and left more than 2,000 people sick.

Preliminary analysis shows the genome is 93 percent similar to an O104 strain of enteroaggregative E. coli, or EAEC, that had been isolated in the Central African Republic and was known to cause serious diarrhoea, the firm said.

But it also includes genes from a different E. coli strain called enterohaemorrhagic E. coli, or EHEC, it added.

"(It) acquired sequences that appear to be similar to those involved in the pathogenicity of haemorrhagic colitis and haemolytic-uremic syndrome (HUS)," BGI said.

HUS is a potentially life-threatening condition in which so-called Shiga toxins exuded by the proliferating germs lead to kidney injury or failure.

"The analysis further showed that this deadly bacterium carries several antibiotic resistance genes, including resistance to aminoglycoside, macrolides and beta-lactam antibiotics: all of which makes antibiotic treatment extremely difficult," the firms said.

Separately, Life Technologies Corp. of Carlsbad, California, said its own early analysis indicated the microbe was a "new hybrid" in which EAEC and EHEC had combined, and this could provide insights into the germ's aggressiveness.

After further work to confirm these findings, the company should be able to develop customised kits designed to detect the hybrid strain, it said.

The World Health Organisation (WHO) said in Geneva earlier that the strain of a lethal bacteria was "very rare" and had never been seen in an outbreak form before.

"It has been seen in sporadic cases and is very rare," Gregory Hartl, the WHO spokesman, said.

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