Industrial disinfectants do not select for resistance in Listeria monocytogenes following long term exposure

Listeria monocytogenes is a food-borne pathogen that can persist for years in food processing plants. It has been hypothesized that this could be due to the development of tolerance or resistance to the disinfectants used. The purpose of the present study was to determine whether biocide resistance or tolerance would evolve in L. monocytogenes under continued selection in three industrial disinfectants. L. monocytogenes EGD was exposed to Desinfect CL (hypochlorite) and Incimaxx DES (peracedic acid and hydrogen peroxide) for several hundred generations. This caused no increase in the minimal inhibitory concentration (MIC) to the disinfectants, whereas exposure to Triquart SUPER (quaternary ammonium compounds) caused a two- to four-fold increase in MIC. Exposure to gentamicin, which was used as a positive control, caused an 8 to 256-fold increase in MIC for several aminoglycosides. Despite the low level of tolerance, the populations adapted to Triquart SUPER were still sensitive to killing with this disinfectant at 0.0125%, which is much lower than in-use concentrations (1-5%). Our data are in agreement with the fact that finding strains with high acquired resistance to disinfectants is rare, and that the disinfectants are still efficient for controlling microorganisms such as L. monocytogenes.