DENVER — Two Colorado farmers whose cantaloupes were tied to a 2011 listeria outbreak that killed 33 people pleaded guilty on Tuesday to misdemeanor charges.

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

“These young men are stepping up because it happened on their watch,” Forrest Lewis, a lawyer for Eric Jensen, said in court.

A sentencing hearing has been set for Jan. 28.

The charges carry penalties of up to six years in prison and $1.5 million in fines. Lewis said in court that the brothers have no criminal record. The Jensens previously filed for bankruptcy.

A statement from the Jensens’ attorneys says the brothers were shocked and saddened by the deaths, but the guilty pleas do not imply any intentional wrongdoing or knowledge that the cantaloupes were contaminated.

The brothers have sued the safety auditor who gave their farm a “superior” rating just before the outbreak — the deadliest case of foodborne illness in the nation in a quarter century.