DENVER (AP) -- Two Colorado farmers whose cantaloupes were tainted with listeria have filed a lawsuit blaming a food-safety auditor that didn't pick up safety problems and gave the farm a "superior" rating just a month before the nation's deadliest case of foodborne illness in a quarter century.
Eric and Ryan Jensen owned Jensen Farms, which sold melons connected to a 2011 listeria outbreak that killed 33 people.
The Jensens were charged last month with introducing adulterated food into interstate commerce and are expected to plead guilty Oct. 22 under a deal with federal prosecutors.
The Jensens filed a lawsuit Tuesday against PrimusLabs, a Santa Maria, Calif., food safety auditor that checked Jensen Farms in July of 2011. The PrimusLabs auditor didn't note that the Jensens' processing system posed a risk of contamination.
The Jensens, who have since filed for bankruptcy, argue that they asked the food-safety auditor about a new processing system, which removed a step of rinsing the melons with chlorinated water. According to the Jensens' lawsuit, the PrimusLabs auditor "did not warn Jensen that the new system created a hazard or a risk of contamination."
A call to PrimusLabs Thursday wasn't immediately returned. The Jenses are seeking unspecified damages and legal fees.
According to the FDA, conditions at Jensen Farms in southeast Colorado led to the 2011 outbreak. Federal investigators said the melons likely were contaminated in the farm's packing house because of dirty water on the floor and old, hard-to-clean equipment.
Officials said people in 28 states ate the contaminated fruit, and 147 required hospitalization.
The Jensens each faced up to six years in prison and $1.5 million in fines had they been convicted of all of the original charges against them. They are scheduled to change their not-guilty pleas on Oct. 22.
Messages left for the lawyers for the Jensens, Richard Banta and Forrest Lewis, weren't immediately returned Thursday. The PrimusLabs was filed in Prowers County, Colo.
Associated Press Writer Colleen Slevin contributed to this report.