Why can we get very sick from E.coli?

A recent study in the UK is giving insight into the reason that humans infected with E.coli generally suffer serious symptoms.

E.coli produces toxins and one of these has been found in cattle to help the bacteria to colonise the gut and this seems to increase the transmission into the cattle herd.

Cattle do not have any symptoms from these toxins, but in humans the symptoms can range from diarrhoea with or without blood to kidney disease, which can be severe and life threatening.

The research was done at the Moredun Research Institute, Roslin Institute (University of Edinburgh), Biomathematics and Statistics Scotland and was funded by Food Standards Agency and Food Standards Scotland. It was published in the journal PLOS Pathogens.

Enterohaemorrhagic E. coli (EHEC) O157 is the subset of E.coli which is primarily responsible for the severe symptoms.

The study has found that it is the specific Shiga toxins from this type of E.coli which encourage the bacterial fgrowth in the intestinal tract of cattle. The most dangerous toxin subtype is Stx2a.

Dr. Tom McNeilly, from the Moredun Research Institute, said; “Our study shows for the first time that Stx2a toxin plays a key role in allowing E. coli O157 to colonize the cattle gut, increasing the ability of Stx2a positive bacteria to transmit between animals and shed at high levels into the environment. This matters because most human infections are thought to originate from cattle, and infections with E. coli O157 strains containing Stx2a are associated with more severe forms of human disease.”

The study found that STx2a is a quicker producer than other toxins, which allows the bacteria to survive longer in the gut. This means that they are more likely to be shed by the cattle into faeces, which increases the opportunity for other cattle and potentially humans to come in contact with the bacteria.