ABC News reported today that three separate strains of E. coli O157:H7 have been found in a Nestle USA cookie dough processing plant.  ABC’s Briant Hartman writes about the E. coli testing:

Those tests, according to sources familiar with the investigation and confirmed by the FDA, determined the genetic fingerprint of the E. coli found at the plant is different than E. coli that has been linked to a 30-state outbreak that has sickened at least 72 people.

Sources also say an altogether different strain of E. coli was found in dough recovered from the home of a victim – E. coli O124.

FDA inspectors and CDC investigators have used several different testing methods during the outbreak.  Among them is Pulsed Field Gel Electrophoresis, or PFGE.  PFGE involves finding a bacteria’s "fingerprint" by cutting the bacteria’s DNA into tiny pieces and using a gel to separate the pieces from one another, creating a pattern, or fingerprint for each strain of bacteria. Scientists from public health laboratories around the nation are able to compare fingerprints isolated from patients and from food. When PFGE patterns from bacteria isolated from a person’s stool and from food are indistinguishable, this strong evidence is combined with epidemiologic and environmental data to prove that a food, like cookie dough, is the source of a person’s illness.

Investigators have not yet been able to determine how the cookie dough became contaminated with E. coli – whether it was from an ingredient or from environmental contamination is yet to be determined, and may never be known.

"There should be no confusion.  The finding of multiple strains of pathogenetic E. coli in either retained samples or someones home does not diminish the link between Nestle and the illnesses of 72 people", said William Marler, attorney for two dozen of the victims.