German E. coli strain combines deadly properties of two pathogens
The E. coli strain that infected thousands in Germany, killing more than three dozen, has now been scrutinized by researchers who say the bug might have been so deadly because it combines the powers of two other types of E.coli — enabling it both to stick fast to the inside of the gut and to release a deadly toxin. This type of bacteria’s “stickiness” might abet the toxin’s absorption, leading to the unusually high number of cases of hemolytic-uremic syndrome, a potentially fatal kidney disorder, they report.
The E. coli strain responsible, O104:H4, appears to produce the same toxin, called a Shiga-like toxin, typical of enterohemorrhagic E. coli—the pathogen often associated with worst-case food outbreaks and known for causing hemolytic uremic syndrome.
Further, the bacteria have the ability to clump together, like a stack of bricks, and adhere to cells that line the intestines. This clumping property is characteristic of enteroaggregative E.coli, a pathogen linked to diarrhea outbreaks in developing countries, especially in children.
To make the new analysis, researchers at the University of Munster collected stool samples from 80 patients infected in the German outbreak and analyzed the genes of the E. coli they found, as well as several properties of the strain. The findings were published online early in The Lancet Infectious Diseases.
In a related commentary, Hugh Pennington, an emeritus professor of bacteriology from the University of Aberdeen, said the researchers had speculated “very reasonably.”
At least 39 deaths, 810 cases of hemolytic syndrome, and 2,684 other cases had been reported to health agencies as of Monday, the authors report—much higher than the roughly 1,000 cases, and 60 hemolytic uremic syndrome cases, Germany normally experiences each year.
The researchers said that other reasons the outbreak was so deadly are still unknown—maybe antibiotic resistance played a role, or perhaps conditions are simply more suitable now for this combination strain to spread through humans (a different strain with these two properties was behind a 10-person outbreak of hemolytic uremic syndrome in France 15 years ago).
Whatever the reason, this is a bug to be reckoned with:
“Although we lack an explanation for increased virulence, this outbreak tragically shows that blended virulence profiles in enteric pathogens introduced into susceptible populations can have serious consequences for infected people.”
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