Scientists seek answers from origins of ′chimeric′ E. coli | Science| In-depth reporting on science and technology | DW | 03.06.2011
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Science

Scientists seek answers from origins of 'chimeric' E. coli

Scientists are examining the results of a genetic sequencing of the new E. coli strain. This new variety, which has sickened thousands in Europe, seems to be a product of two previously known infectious types of E. coli.

Petri dish

German researchers continue to look for the strain's source

As of Friday, while German scientists struggled to isolate the source of the E. coli outbreak, epidemiologists and microbiologists remain unsure as to how they can uncover the secrets of this new infectious strain - and ultimately, battle it.

Earlier in the week, a team of German and Chinese scientists said that they had sequenced the genome of the bacteria, finding that it contained elements from two other previously known strains, O104:H4 and EAEC 55989.

O104:H4, which is a rare, enterohemmorhagic - or bloody diarrhea-inducing - strain, has only been documented in scientific literature once before. In 2005, a 29-year-old woman was admitted to a Korean hospital and was treated for the infection and later recovered.

This E. coli represents a new serotype, or sub-species variant for this kind of bacteria. It also has a "shiga toxin," which targets kidney cells and has the ability to enter the blood stream.

The Beijing Genomics Institute team also said on Thursday that the new bacteria has "93 percent sequence similarity" with EAEC 55989, another type of E. coli that is known to have an advanced ability to "colonize" the human stomach - that is, to latch on and reproduce quickly.

Woman with beaker

Microbiologists say that the new strain sustained a 'horizontal gene transfer'

But this combined ability, to produce a potentially deadly toxin and to easily reproduce within humans, is precisely what bacteriologists and public health officials are worried about.

"In a way, you have the worst of both worlds," explained Anthony C. Hilton, a microbiology researcher at Aston University in Birmingham, England, in an interview with Deutsche Welle. "This is a brand-new strain that attaches in a new way, with a whole new toolkit to persist and infect."

Horizontal gene transfer

Microbiologists think that this new combination strain was most likely created through a process called "horizontal gene transfer." While vertical gene transfer is when a parent passes a gene to a child, horizontal gene transfer is when genetic material from one organism passes into another organism, without any offspring relationship.

Just as humans get viruses, bacteria can get viruses, too. A virus can inject its genetic material into bacterial DNA, where it essentially hijacks the bacteria's genetic structure and forces it to reproduce.

Horizontal gene transfer is understood to happen mostly in sewage reservoirs, and in the guts of warm-blooded animals.

"We know that E. coli evolve in real time," said Jonathan Fletcher, a senior lecturer in microbiology and the medical science faculty at the University of Bradford in the United Kingdom. "We know E. coli and other bacteria are continually gaining and losing genes."

A focus on solutions

The most important thing to fight the outbreak, which has already claimed more than a dozen lives in Germany, is to find the source and to keep it from spreading, said Lothar Beutin, the laboratory head at Germany's Federal Institute for Risk Assessment, in a Deutsche Welle interview.

Spanish cucumbers

Public health officials originally blamed the outbreak on cucumbers

Another important step is to develop a test that can identify the strain. Knowledge of the genetic sequencing could help, scientists say, although it hasn't so far.

"When the Beijing team gets its final sequence, they'll want to compare that with other strains in a sort of E. coli database," Fletcher explained.

But developing a test is mainly a matter of painstaking work, he observed.

"It's the equivalent of going to an absolutely huge parking lot, and you're looking for one particular black [Volkswagen] Golf, that has a blue-painted engine," he said. "You'd essentially have to look in the bonnet of every black Golf."

Scientists working on identifying the source of the outbreak still have a tremendous amount of legwork. In other words: developing a case control study, which involves doing detailed interviews of those who got ill to determine just what exactly made them sick.

But right now, without a way to test for the presence of this super bug, and without knowing its origin, all that can be done is treat and try to prevent it.

Blood flushing

Bloody diarrhea is the typical symptom for the enterohemmorhagic side of the bacteria's genesis. Since the other side of the strain attacks the kidney, another of its symptoms is bloody urine.

"You don't fight the bug, you fight the symptoms," said Beutin, adding that traditional antibiotics usually make it worse.

Lettuce fields

Many people in Germany are eating less lettuce

Physicians call this supportive therapy, which in this case involves dialysis and plasma exchange - essentially flushing out the kidneys and blood.

In the only other documented case involving the O104:H4 strain, that's exactly what kept a 29-year-old woman in Korea alive. According to a June 2006 scientific paper published in the Yonsei Medical Journal, an English-language Korean medical journal, the woman received four days of dialysis and plasma for two weeks. Although her case involved the acute kidney complication, she recovered after spending 21 days in the hospital.

'The most lethal E. coli'

But because this strain has been so virulent, so fast, bacteriologists and epidemiologists generally agree that this new, "chimeric" strain is a serious concern.

"At the present state, this seems to be the most lethal E. coli [that we've seen so far]," Beutin said.

Until the source of the contamination is pinpointed, people should heed warnings to avoid or thoroughly clean cucumbers, tomatoes and lettuce - and that goes for Beutin himself.

"We avoid eating salads," he said. "We try to clean fruits more and to wash things."

"Initially I had planned my holidays starting Monday, but now - there's a lot of work to do," he added.

Author: Sonya Angelica Diehn
Editor: Cyrus Farivar

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