Sensitivity of Listeria monocytogenes to sanitizers after exposure to a chemical shock

We tested the hypothesis that exposure of Listeria monocytogenes to sublethal levels of sanitizers (chemical shock) could affect survival to a subsequent exposure to lethal levels and the ability of the cells to attach to stainless steel surfaces. L. monocytogenes was exposed to an acidic anionic sanitizer, a chlorine-based sanitizer, an iodophor, and a quaternary ammonium compound, as well as to citric, lactic, and propionic acids. The cells were exposed to sublethal levels of each sanitizer for up to 60 min (chemical shock), followed by exposure to either the minimum inhibitory concentration (MIC) for 48 h, to the lethal level for 48 h, or to the MIC for 40 min followed by the lethal level for 48 h. No significant difference in survival was observed with most of the sanitizers used. However, exposure to a chemical shock with the acid anionic sanitizer for at least 10 min resulted in survival of the cells in the MIC of this sanitizer, as well as in the lethal level, but only when the cells were first exposed to the MIC for 40 min. Deliberate dissociation of citric acid by pH adjustment also resulted in survival of chemically shocked cells to lethal levels of this acid, suggesting that exposure to the dissociated form somehow enabled cells to survive exposure to lethal levels of the acid. Chemical shock did not affect attachment of the cells to stainless-steel chips.