Personal Injury Law

Massachusetts Health Investigators Find Listeria At Whittier Farms

By Bill Marler, Esq.

The Associated Press reported this morning that Massachusetts Health Investigators probing the source of the deadly listeria, found the identical strain (DNA fingerprint is called Pulse Field Gel Electrophoresis, or PFGE) that killed four people at the Whittier Farms processing plant.  The strain was found in seven bottles and on the floor near the homogenizer at the Shrewsbury plant.  Different listeria strains were found inside four other bottles of milk and at three different areas inside the plant — in a drain, in a bottle washer and in an empty unwashed bottle. More than 100 samples were taken.

What is PFGE?

When a sample is taken from either a piece of meat, poultry or milk that is contaminated with a dangerous form of bacteria, such as E. coli O157:H7, listeria, or campylobacter, it can be cultured to obtain and identify the bacterial isolate. If a person consumes some of the 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 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. 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.

Full post as published by Marler Blog on January 17, 2008 (boomark / email).