For the study, researchers cultivated seven-day-old L. monocytogenes biofilms on food contact surfaces common to packinghouses, including stainless steel, polyvinyl chloride, polyester, low-density polyethylene, and rubber. Biofilms on the surfaces were exposed to treatments of 200 parts per million (ppm) chlorine, 400 ppm quaternary ammonium compound (QAC), or 160 ppm peroxyacetic acid (PAA). The experiment was run on surfaces that were free of defects and organic matter, and then run again on surfaces with defects and organic matter.