Marler Clark is in the process of updating www.fsis-pfge.org through 2009. We have taken the initiative to publish this information in the hopes that it will provide assistance to government agencies – Federal, State and Local – as well as individuals, in ascertaining the source of E. coli O157:H7 infections. More broadly, Marler Clark hopes to spur greater communication amongst government agencies to better protect the public from serious health threats associated with contaminated meat.
The website contains Pulse Field Gel Electrophoresis (PFGE) patterns of particular strains of E. coli O157:H7 associated with recalls of ground beef since 2000. Comparison of PFGE patterns sampled from individual persons infected with E. coli O157:H7 may allow the identification of the source of an individual’s illness. It is for this reason that Marler Clark has created this website, hoping to advance the cause of food safety, and to assist health departments in determining the source of outbreaks.
What is PFGE?
When a sample is taken from either a piece of meat or poultry that is contaminated with a dangerous form of bacteria, such as E. coli O157:H7, Salmonella, Shigella, Listeria, or Campylobacter, it can be cultured to obtain and identify the bacterial isolate. If a person consumes some of the contaminated meat or poultry, and becomes infected as a result, a stool sample can then be cultured to obtain and identify the bacterial isolate. These bacterial isolates are then broken down into their various component parts creating a DNA "fingerprint".
The process of obtaining the DNA fingerprint is called PFGE. This technique is used to separate the DNA of the bacterial isolate into its component parts. It operates by causing alternating electric fields to run the DNA through a flat gel matrix of agarose, a polysaccharide obtained from agar. The pattern of bands of the DNA fragments — or “fingerprints” — in the gel after exposure to the electrical current is unique for each strain and sub-type of bacteria. By performing this procedure, scientists can identify hundreds of strains of E. coli O157:H7 as well as strains of listeria and campylobacter, and other pathogenic bacteria.
The PFGE pattern of the bacteria can then be compared and matched up to the PFGE pattern of the strain of infected persons who consumed the contaminated product. When PFGE patterns match, they, along with solid epidemiological work, are proof that the contaminated product was the source of a person’s illness.