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Verotoxin: How to detect contamination and ensure safe food

Verotoxin-producing EHEC bacteria are a common cause of food-borne infections. Here’s what food producers should know about the risk associated with the pathogen and the methods of detection.

The Escherichia coli bacterium (abbreviated E. coli) occurs naturally in the intestinal flora of humans and animals. Most E. coli bacteria are harmless, however there are some pathogenic strains that may cause serious infections. One of these pathogenic strains is known as the enterohaemorrhagic E. coli („EHEC“). These bacteria form verotoxin or shigatoxin and are therefore also referred to as verotoxin-producing E. coli („VTEC“) or shigatoxin-producing E. coli („STEC“).

Infections caused by STEC/VTEC are among the most common bacterial food-borne diseases. Symptoms include watery or bloody diarrhea, nausea, stomach pains and fever, sometimes progressing to haemorrhagic colitis and even haemolytic uraemic syndrome (HUS). The main contamination sources are meat products, in particular raw or undercooked meat from cattle, sheep, goats or deer. Unpasteurized milk products may be contaminated, too. Moreover, bacteria may get into drinking water, fruit, vegetables and other herbal products via contaminated water or fertilizer.

Detection of STEC/VTEC/EHEC in food

Since the infectious dose of STEC/VTEC/EHEC is very low, zero tolerance applies to ready-to-eat food. Regularly tests are therefore inevitable in food processing facilities. Since detection of the pathogenic bacteria is very time-consuming using traditional microbiological methods, laboratories usually use faster procedures such as molecular biological tests (PCR). According to regulations, foodstuffs are considered contaminated as soon as a single STEC/VTEC/EHEC bacterium is present in 25 gram of specimen. In order to make such low concentrations detectable, an overnight sample enrichment must be carried out. After enrichment, the contamination can be detected.