Understanding presumptive positives in PCR testing

Specific DNA based PCR methods enable STEC E coli to be identified against a background of other closely related non-pathogenic E coli and other non-target microorganisms. PCR is a rapid method used to determine the absence or presence of STEC E coli and is done using a sample taken from an overnight enrichment broth. However, care should be taken with interpreting the results, as a presumptive positive PCR result doesn’t necessarily mean the microorganism is present and as sometimes fragments of DNA from other strains or species present in the broth can combine and provide false presumptive positive results. Therefore, it’s extremely important to treat any presumptive positive PCR results with caution, until they have been confirmed. To confirm presumptive PCR results, you must also isolate the organism by growing it on a plate and doing PCR using an isolated colony from that plate.

Campden BRI have a UKAS accredited next day PCR based method for the detection of the European Big 6 STEC in sprouted seeds and the USA Top 7 STEC detection in red meats, with a containment level 3 laboratory to quickly carry out the important confirmation work

Get in touch find out more about food microbiology testing methods
Julie Archer
+44(0)1386 842135
julie.archer@campdenbri.co.uk