Wetenschap - 7 juni 2011

The cucumber and the bean sprout

The source of the deadly EHEC bacteria in Germany is still anyone's guess. After the cucumber, the bean sprout had come under suspicion. The latter is a more likely culprit, says Wageningen food microbiologist Wilma Hazeleger.

In teaching, we use the bean sprout as a model vegetable because it contains a lot of bacteria. This is due to the way the sprouts are cultivated. The seeds are soaked in a water bath at a high temperature - exactly what bacteria are fond of. Bean sprouts can therefore have high concentrations of bacteria. Most of these however do not make us sick.
EHEC is a gut bacterium belonging to the E. coli group. It had shown up in the past in bean sprouts in China; consignments of meat were infected in the United States, perhaps due to slaughter under unhygienic conditions. The bacteria produce a poisonous substance which causes the problems. Cattle are often carriers of EHEC but they do not fall sick themselves.
We still do not know where the source of the current infection is. Tracing this is very difficult, because the incubation time of EHEC is one week to 10 days. Moreover, infected persons do not go to the doctor directly on the first day. Patients therefore have to recall what they have eaten two weeks ago. What if the bacteria were in the water? The source could most probably never be traced. Or the bacteria are spread in a horticultural farm by an employee suffering from diarrhoea. This can take place easily because a sick person excretes millions of bacteria and it takes just a hundred to fall sick. The source is perhaps not traceable anymore, but EHEC can show how things work in microbiology and is an interesting case study.
There is no need to panic. You can continue to eat sprouting vegetables, but blanching bean sprouts to kill the bacteria would be a sensible thing to do. Furthermore, it's not wise to eat raw meat, but you can continue eating it rare or medium, as the inside of the meat is sterile in principle. Just make sure that the piece of meat is seared thoroughly, as bacteria are only found on the outside. Always cook ground meat well.