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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, 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 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.
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The
use of a sophisticated technique called Pulse Field Gel
Electrophoresis (PFGE) enables scientists to ascertain the
relatedness of E. coli strains found in samples taken from
patients. The Centers for Disease Control (CDC) have established
an electronic database that enables epidemiologists to quickly
identify and compare infectious strains of bacteria by comparing PFGE patterns. Currently,
however, PFGE is available only in a small number of state
public health laboratories.
VIDEO
How
E. coli's toxins are
released
in the intestine
(570K) (QuickTime)
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