Detection of Shiga Toxin producing Escherchia coli (STEC)
By Julie Archer - 30 May 2014
There are hundreds of serotypes of E. coli. Many can be found in the intestines of animals. Most are harmless; however, some strains can cause severe illness, including haemorrhagic diarrhoea and Haemolytic Uraemic Syndrome. These strains produce 'shiga–like' toxins and are known as Shiga toxin-producing E. coli (STEC) or Verocytotoxin–producing E. coli (VTEC). STEC were first identified as food borne pathogens in 1982, following outbreaks associated with E. coli O157:H7.
In May 2011, a novel strain of STEC Escherichia coli O104:H4 caused a serious outbreak of food borne illness focused in northern Germany. It affected approximately 4000 people and there were a number of deaths; this outbreak was associated with imported Fenugreek seeds. Since this outbreak STEC have become a key area of concern to the European food industry.
Pathogenic bacteria can contaminate seeds intended for sprouting during their production and it is possible that their numbers could increase during germination and sprouting, due to the elevated temperatures and moist conditions used. Therefore sprouted seeds could become a vehicle for transmission of foodborne pathogens, if they are consumed uncooked or minimally processed.
Another high risk food for STEC contamination is raw meat, especially raw ground beef. The reported global prevalence of E. coli O157:H7 in cattle (prior to slaughter) varies from 0.2% to 27.8% and that of non–O157 STEC is 2.1% to 70.0%. In this year alone there have been numerous reports of STEC contamination of beef noted in Europe through Rapid Alert System for Food and Feed (RASFF).
New EU legislation requires the analysis of sprouted seeds for 6 STEC serotypes (O157, O145, O111, O103, O26 and O104:H4) prior to release onto the market. There is also new draft guidance on actions to take if foods are found to contain STEC; this guidance includes (in ready to eat foods and some raw meat products), recall of all of the products concerned. Because STEC are highly pathogenic, testing laboratories require an enhanced level of containment to handle these organisms. We have one of the very few of these facilities in the UK, enabling us to undertake STEC testing.
We have spent two years developing, optimising and further validating a PCR method for testing for these STEC types as part of a member funded Research Programme. Advantages of PCR testing are:
- Detection of low numbers (detection level of 2–40 colony forming units per 25g)
- The absolute specific nature of the method, giving complete confidence in results.
- Discrimination of the target STECs noted in the Regulations from closely related organisms.
- Rapid results
STEC contain defined DNA targets known to be characteristic of this group of organisms; the shiga toxin–producing genes (stx1 and stx2) are detected by the 'GeneDisc STEC and pathogenic E.coli O157' PCR method that we use. If you would like to know more about this service and the requirements of the legislation, please get in touch.