The O104:H4 E. coli strain. (Photo courtesy Manfred Rohde, Helmholtz-Zentrum fuer Infektionsforschung (HZI)/Getty Images)
The rare strain of E. coli that has killed 39 people and sickened thousands in Europe combines the abilities of two known E. coli pathogens to create a dangerous, virulent blend, new research shows.
A team at the University of Münster looked at the genetic profile of the circulating strain, identified as O104:H4, and found it produces a toxin called Shiga similarly to one group of E. coli, but adheres to cells that line the gut in the same manner as a diarrhea-causing group of E. coli.
The “enhanced adherence” to cells in the gut could be causing more absorption of the toxin, wrote the authors of the paper, published by the Lancet Infectious Diseases, and could be one explanation for the high number of patients who have developed kidney failure.
Haemolytic uraemic syndrome, which attacks the kidneys and is considered the worst-case complication from an E. coli infection, has been found in 810 of the more than 3,500 infections caused by the outbreak, or about 23 percent.
The Shiga toxin is also produced by the most well known strain of E. coli, 0157:H7, which has caused famous outbreaks of contamination in spinach and beef, but only 5 to 10 percent of these infections usually develop into kidney failure.
Phillip Tarr, the director of gastroenterology and nutrition at Washington University School of Medicine, who was not involved in the study, said the results show what the toxin is capable of when carried by the right organism.
“When the virulent traits combine in this binary effect we see devastating consequences,” Tarr said. “The combination appears to be extraordinary.”
The strain is not new — according to the researchers there was an isolated case of it in Germany in 2001 and another in South Korea — but this year’s outbreak is the first time it has spread widely.
“The high apparent fatality rate and high apparent kidney failure rate is extremely disturbing,” said Tarr. “This is clearly an organism that must be reckoned with.”
Microbiologist Hugh Pennington of the University of Aberdeen, who wrote an accompanying comment in the Lancet, said the study gives a foundation to understanding the strain but there are many unknowns left to resolve before they can build a complete picture.
The E. coli strains that most commonly sicken humans are generally hosted in cattle and then spread through contamination. But it is not yet known if the O104:H4 strain lives in cattle or even if it could be from a human source, he said.
“There are still quite a lot of unanswered questions about where this organism has its natural home and if it is common or not,” Pennington said. It is possible the strain is very rare, that the outbreak was a one-off, but further research may reveal it’s quite widespread.
Investigators in Germany identified bean sprouts as the contaminated produce spreading the bacteria earlier this month. The victim patterns appeared unusual — the majority are young and middle-aged women — but that pattern could be explained by the food vector itself and food choices, Pennington said. On the other hand, E. coli O157:H7, which is well-known from outbreaks from from contaminated produce and meat in the U.S., usually hits the elderly and young children hardest.
As more investigation is done into where the strain came from and how to best treat it, the outbreak continues to shine a harsh light on food safety practices.
“We are going to have to have a rational discussion about the safety of non-irradiated fresh fruits and vegetable,” said Tarr. He and Pennington both called for better implementation of existing safety measures.
“[This outbreak] is a useful reminder that these bugs have not gone away and continue to challenge our food safety system,” said Pennington. “They are quite good at finding the weaknesses.”