Germany’s recent enormous E. coli outbreak points to the need to better identify and understand the virulence genes involved with this pathogen, said Pina Fratamico, PhD, a lead researcher at the U.S. Department of Agriculture’s Center for Food Safety who has worked to draw attention to lesser-known types of E. coli.
So far, 36 people have died and more than 3,000 have been sickened in the outbreak, which was originally blamed on cucumbers grown in northern Spain but has apparently been traced to contaminated sprouts from Germany. The strain of E. coli involved, 0104:H4, has never been associated with a significant foodborne outbreak. More than 700 of the cases so far have progressed to hemolytic uremic syndrome (HUS), a type of kidney failure that is usually only seen in about 7% of E. coli cases, according to Dr. Fratamico.
Genome sequencing conducted in China suggests that the bacterium is a type of hybrid that combines multiple virulence factors. While it carries the Shiga toxin 2 gene, it probably did not start out as a Shiga toxin-producing E. coli, or STEC, Dr. Fratamico said. “It’s lacking the eae gene and the hemolysin gene, which are found in most enterohemorrhagic E. coli,” she said. “That suggests that it probably started out as an enteroaggregative form of E. coli and picked up the Shiga toxin 2 gene through horizontal gene transfer. It probably also has other virulence genes that we’ll find out more about.”
And that, Dr. Fratamico said, underscores an essential avenue for future E. coli research. “Serogroup is important, but equally important, if not more so, is understanding what all the key virulence genes are. We can’t just look for [shiga toxin-producing E. coli]. Had we done a PCR [polymerase chain reaction] assay looking just for the combination of Shiga toxin and eae genes, which is common, we would have missed this strain.” (In fact, that’s what happened with the original STEC assays that inaccurately pinned the outbreak on Spanish cucumbers, which were contaminated with E. coli, just not with this particular supertoxin.)
Could the new hybrid strain of E. coli, which apparently originated in the Central African Republic, pop up again in Europe or elsewhere? It’s certainly possible, Dr. Fratamico said. “We need to understand what the reservoir is … how it gets into food, and what the characteristics of the strain are in detail to better know whether it is likely to happen again,” she said.