Abstract: In this study, a modified CDC biofilm reactor was designed and the components of the reactor were primarily machined using Delrin plastic. Initially, biofilms grew well using the reactor unit. However, after approximately five runs of the reactor, bacterial growth was inhibited and biofilms no longer formed. To troubleshoot the problem, bacteria were grown in the presence of broth alone or in the presence of broth and Delrin plastic. It was determined that the reactor components containing Delrin plastic prevented growth of bacteria and the formation of biofilm. It appeared that the repeated exposure to autoclave temperature and pressure caused the Delrin plastic to decompose and leach formaldehyde into the broth, which inhibited bacterial growth. Based on these results, we propose that Delrin plastic should not be used in bacterial growth devices.