Escherichia coli, better known as E. coli, is a common inhabitant of the human gut. Most E. coli strains are harmless but a few can cause serious illness and even death. One such group, known as enterohaemorrhagic E. coli (EHEC) or Shiga-toxin producing E. coli (STEC), cause bloody diarrhoea, and in some people, Haemolytic Uraemic Syndrome (HUS) which can lead to anaemia, kidney failure and death.
EHEC used to be known as the ‘hamburger disease’ as it was most frequently caught as a result of eating undercooked contaminated meat (cattle can have EHEC in their guts too). But in recent years, a growing number of outbreaks have been associated with vegetables instead. One such outbreak is currently happening in Europe, with 14 people dead and hundreds more seriously ill. A Spanish organic vegetable producer is thought to be the source of the outbreak, and Austria’s food safety agency has ordered a recall of their cucumbers, tomatoes and eggplants.
Recently, researchers have shown how plants become contaminated with EHEC, and it makes scary reading. Most people would think that as long as they gave their vegetables a decent rinse before putting them in their salad, then all would be well. If only it were that simple. It turns out that the bacteria aren’t just hanging around on the surface of the plant. Shaw and colleagues (1) showed that EHEC attach to the very cells that open and close the pores plants use for gas exchange. From here, the bacteria can then get inside of the plant cell, where no amount of rinsing can reach them. This does raise an interesting question, are plants just another environment that E. coli can survive in or is this actually a strategy for getting inside of an animal?
So how might the vegetables have been contaminated? Water is one likely source; plants could have been irrigated with contaminated water, or contaminated water could have been used during processing or storage of the harvested vegetables prior to distribution. Other potential sources of contamination could be the use of inadequately composted or raw animal manures or sewage as compost. Whatever the source, lets hope they find it and deal with it. In the meantime though, I think I’m going to stick to well cooked hamburgers, without the salad. I was never that keen on cucumbers anyway.
1. Shaw RK, Berger CN, Feys B, Knutton S, Pallen MJ, Frankel G (2008). Enterohemorrhagic Escherichia coli exploits EspA filaments for attachment to salad leaves. Appl Environ Microbiol. 74(9):2908-14.
UPDATE 01/06/11: Seems Germany may have been too hasty to blame Spanish cucumbers as being the source of the outbreak. Lets hope they find the source quickly as, according to an article in the Guardian newspaper, the death toll apparently now stands at 16 with over a thousand people infected and 373 suffering from HUS.
UPDATE 02/06/11: Deaths apparently at 17 and people with HUS now at 470. Scarily, the NZ Herald have run an article from the Independent which ends:
Infection can be avoided by washing all vegetables.
Yikes. Cook more like.