DENVER — Eric and Ryan Jensen pleaded guilty on Oct. 22 to misdemeanor charges under a deal with federal prosecutors. The two brothers operated Jensen Farms, the cantaloupe processing operation that the Food and Drug Administration found was the source of a Listeria outbreak in 2011. The outbreak led to 33 deaths and 147 illnesses.

Eric and Ryan Jensen entered the pleas in federal court in Denver to six counts of introducing adulterated food into interstate commerce.

A sentencing hearing has been set for Jan. 28. The brothers could face a maximum of six years (one year for each count), but federal guidelines suggest a sentence of 4 to 10 months per count. Additionally, each brother could be fined up to $250,000 for each of the six counts.

Court documents state the defendants set up and maintained a processing center where cantaloupes were taken from the field and transferred to a conveyor system for cleaning, cooling and packaging. The equipment should have worked in such a way that the cantaloupe would be washed with sufficient anti-bacterial solutions so that the fruit was cleaned of bacteria in the process, according to the Department of Justice.

In May 2011 the Jensen brothers allegedly changed the cantaloupe cleaning system. The new system, built to clean potatoes, was installed and was to include a catch pan to which a chlorine spray could be included to clean the fruit of bacteria. The chlorine spray, however, was never used. The defendants were aware that their cantaloupes could be contaminated with harmful bacteria if not sufficiently washed. The chlorine spray, if used, would have reduced the risk of microbial contamination of the fruit.

Investigation by the F.D.A. and the Centers for Disease Control and Prevention determined that the defendants failed to adequately clean their cantaloupe. The actions allegedly resulted in at least six shipments of cantaloupe contaminated withListeriamonocytogenes being sent to 28 different states.