Food Biochemistry and Food Processing

31 Emerging Bacterial Foodborne Pathogens and Methods of Detection 721

Figure 31.1.Use of competitive PCR to quantify pathogens. A.A PCR mixture is made up that contains serially
diluted DNA from the sample and a constant amount of a competitive PCR fragment. The competitive fragment has
the same sequence at its ends, but an internal deletion makes it shorter than the native pathogen gene for ease of
distinguishing between the PCR products. B.During PCR amplification, primers complementary to the target gene in
the pathogen amplify both the target gene and the competitive gene. C.The products of the PCR are analyzed by
agarose gel electrophoresis. As the dilution of the sample DNA increases, the resulting PCR product decreases. The
intensities of the bands can be compared in order to quantify the number of target genes from the pathogen in the
original sample.