How is E. coli infection diagnosed?
How is an E. coli Infection Diagnosed?
Infection with E. coli O157:H7 or other Shiga toxin-producing E. coli is usually confirmed by the detection of the bacteria in a stool specimen from an infected individual. Most hospital labs and physicians know to test for these particular bacteria, especially if the potentially infected individual has bloody diarrhea. Still, it remains a good idea to specifically request that a stool specimen be tested for the presence of shiga toxin-producing E. coli when it is submitted to the lab for testing.
Trace-back and source identification
E. coli O157:H7 is now commonly “fingerprinted.” 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, Salmonella, 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 “fingerprint” of the bacteria can then be compared and matched up to the “fingerprint” of isolates from persons who consumed the contaminated product. When DNA “fingerprints” match, 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. By performing this procedure, scientists can identify hundreds of strains of E. coli O157:H7 as well as strains of Listeria, Salmonella, and Campylobacter.