The findings, reported in Mushroom News, may have implications for extending mushroom shelf life as well because the process that remove soil residue off the mushrooms may prevent spoilage caused by non-pathogenic bacteria, as well.

"We have found that the washing process limits growth of pathogens such as Listeria and Salmonella in whole mushrooms," Robert Beelman, of Pennsylvania State University at University Park, Pa., said in a statement. "The protective effect of washing was more pronounced in sliced mushrooms, which are more prone to bacterial growth than unsliced ones."

Beelman and Naveen Chikthimmah divided a 33-pound batch of the button variety of mushrooms into two equal groups. One group was washed using a process -- patented by Beelman -- that washes with an antibacterial solution, then a neutralizing solution containing preservative that inhibits browning.

When both washed and unwashed mushrooms were inoculated with food-borne pathogen, the washed mushrooms had significantly reduced growth of both Listeria and Samonella. The pathogens grew more rapidly in sliced mushrooms, but to a significantly lesser degree in the washed ones, the study said.