Dr Anne Carroll
More labs are looking into using PCR in testing for Verocytotoxigenic E.coli (VTEC) in food, says Dr Anne Carroll of the VTEC Reference Laboratory.
VTEC is a type of E. coli that produces a powerful toxin and can cause severe illness. “VTEC causes a spectrum of disease from diarrhoea all the way up to haemolytic uraemic syndrome, which can be life-threatening”, says Anne.
VTEC became known as the ‘burger bug’ as it was first identified in cattle and undercooked burgers. We know now that products which come directly from animals or secondary products such as milk and crops exposed to potentially contaminated water can all contain VTEC.
“There’s been a big change in clinical labs,” says Anne, who adds that food labs may be slightly behind. “A lot of food labs don’t have the capabilities to carry out ISO 13136 testing because they don’t have PCR capabilities.”
The standard for the microbiological examination of food and animal feed is ISO 13136:2012. It includes a real-time polymerase chain reaction (PCR)-based method for the detection of food-borne pathogens. The VTEC reference lab has been using PCR for food testing in recent years, but many labs around Ireland still use older plate-based methods.
Regulators are keen to use the most modern methods such as PCR in testing for VTEC. Dr Kaye Burgess from the Teagasc Food Research Centre says: “Using PCR-based methods can increase the sensitivity in comparison to culture-based methods. This is important because VTEC have a very low infectious dose”.
VTEC testing methodologies have some limitations. Kaye explains: “There can be difficulties in obtaining an isolate from a PCR-positive sample. Also, improvements are needed in growth media to differentiate VTEC sufficiently. This is particularly the case for non-O157 VTEC.”
In recent years, PCR has become much more routine and affordable. It has many potential advantages and would benefit food testing laboratories.
Comments
I agree with the principle of the piece. With a few obvious exceptions, food laboratories are generally commercial entities. They cannot invest in the appropriate equipment and expertise until (generally legislation/retailer driven) demand is there from industry.
Excluding nutrition and NPD work, you will not find too many producers/processors volunteering to undertake routine testing that is not prescribed by law or by retailers (for an illustration see meat speciation sample numbers and number of laboratories offering the analysis, in 2010 vs 2013). This is somewhat of a generalisation but will hold true in most cases.
While PCR has reduced in cost, it is still relatively expensive compared with standard cultural micro methods. This is another problem that will need to be overcome if PCR STEC analysis is to become more 'mainstream' for the food industry