E. coli shows up in the news pretty regularly. Whether it’s in hamburgers or lettuce or flour, the little rascal’s appearance is generally accompanied by reports of ruined kidneys, hospitalization, and sometimes death. On the other end of the spectrum, we read that we all have E. coli in our guts-that it makes Vitamin B12 and Vitamin K (1). So how can something that makes us so sick sometimes live in our guts peacefully the rest of the time?
As it turns out, all E. coli are not the same. Meet the pathogenic enterohemorrhagic E. coli (EHEC), the evil twin of the benevolent K12 E. coli in our guts. The most common type of EHEC is O157:H7, so this is probably how you’d see it referred to in news reports, but there are six major types of EHEC (2).
The biggest difference between the two E. coli is that EHEC has extra genes–extra bits of DNA–which allow them to make toxins, known as shigatoxins (Stx) (2). These toxins travel to the kidneys and kill off kidney cells, which leads, unsurprisingly, to kidney injury and failure (2). They also have another set of genes which allow them to attach to the cells lining the intestine and destroy their nutrient-absorbing microvilli (2). This causes bloody diarrhea/diarrhea in general (2).
As a result, while K12 peacefully curls up next to the intestinal cells, stealing milk sugar (lactose) and making vitamins for us, EHEC sweeps in, wreaks havoc, and is eventually driven off by our immune system (except when it kills us). Yet, they aren’t all that different. EHEC just took in some stray bits of DNA and became a killer, while K12 didn’t and stayed benevolent. Choices have consequences, people.
Also, don’t accept free gifts from strangers.
(1) Review. “The Unexhausted Potential of E. coli.” 2015. Blount, Z.R.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4373459/ *this is fairly technical
(2) FDA, 2013. The Bad Bug Book. “Pathogenic Escherichia coli Group.” pp. 69-79.