Pulse-field gel electrophoresis (PFGE) is the DNA "fingerprinting" method that scientists use to determine the source of bacterial foodborne outbreaks.

How Does PFGE Work?

The DNA of the bacterial pathogen responsible for a foodborne illness is digested into pieces by reacting the isolated DNA with enzymes that are able to specifically break the DNA molecule into individual pieces. The digested DNA is placed at one end of the gel. A pulsing electric field applied across the gel drives the DNA pieces into the gel over a period of hours. The smallest pieces slip through the pores of the gel more quickly, so the pieces are separated as distinct bands in the gel, based on size. The resulting pattern of 30 to 50 bands, which resembles a bar code is the "fingerprint."

What are the Food Safety Implications of PFGE?

Like human fingerprints, each bacteria and its offspring have a unique PFGE pattern. If two bacteria are found with an indistinguishable pattern, it is likely that they have a common source and may be part of an outbreak. A national computer database of PFGE patterns is housed at CDC as part of PulseNet. States submit PFGE patterns of pathogens that have made people sick to the database over the Internet. The computer then automatically scans previously submitted patterns searching for matches, i.e., indistinguishable DNA fingerprint patterns of pathogens that have made other people sick. If a match is found, a signal is given to the submitter that duplicate patterns are present and where they came from, so that an investigation can begin to look for a common source.

What are the Legal Implications of PFGE?

For someone who has been diagnosed with E. coli to be considered part of an E. coli outbreak, the DNA fingerprint of the E. coli bacteria that sickened the person has to be indistinguishable from the DNA fingerprint of the E. coli bacteria that sickened at least one more person. If a food item can be found with the same DNA fingerprint, that food item is considered the source of the outbreak. This connecting of DNA fingerprints between people and food is used to establish legal liability. For example, if 2 or more people ate at a restaurant and contracted E. coli infections, and the DNA fingerprints of those 2 people and a food item at the restaurant were indistinguishable, the restaurant would be liable to the sickened people for all damages related to the E. coli infections, including illness that develop as a result of the E. coli infections, including hemolytic uremic syndrome (HUS).

Even if a food item is not found at the restaurant with the same DNA fingerprint as the bacteria that sickened outbreak victims, the restaurant can still be held liable to the sickened people. In a recent case, we represented people sickened at a restaurant in a situation where: 1. no food item was found with the same DNA fingerprint and 2. more than one food item could have been the vehicle for transmission of the foodborne pathogen. Even so, we negotiated a settlement with the restaurant, and our clients were fairly compensated.

To contact us, please call toll-free at 1-888-377-8900 or submit our online consultation form. Our law firm, Pritzker | Ruohonen has a national practice representing victims of foodborne illness, including E. coli.