According to William Keene, Oregon State Epidemiologist, last week initial lab test results of a Sally Jackson cheese sample taken from a wedding were PCR (polymerase chain reaction) positive, indicating DNA likely linked to the outbreak strain. Today, those results have also been culture confirmed, and are indistinguishable by pulse-field gel electrophoreses (PFGE) to the eight ill persons in Oregon, Minnesota, Washington and Vermont.
When a person consumes contaminated food 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 “fingerprint” of the bacteria can then be compared to the “fingerprint” of isolates from persons who consumed the contaminated product or the contaminated product. When DNA “fingerprints” are indistinguishable, they, along with solid epidemiological work, are proof that the contaminated product was the source of the illness.
The process of obtaining the DNA “fingerprint” is called Pulse Field Gel Electrophoresis, or 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.
To see a partial reall list and inspection reports, see “Sally Jackson Raw Milk Cheese Distribution List for E. coli Recall – Eight Ill in Oregon, Washington, Vermont and Minnesota.”