Relative performance of commercial citric acid and quaternary ammonium sanitizers against Listeria monocytogenes under conditions relevant to food industry

Growth of Listeria monocytogenes in cold temperatures coupled with its tolerance of antimicrobials can promote its survival and persistence in food processing environments. The food industry relies heavily on cleaning and sanitation to control L. monocytogenes; therefore, it is important to understand the environmental context (i.e., temperature) on the efficacy of antimicrobials used in food industry. The minimum bactericidal concentrations (MBCs) of an "eco-friendly" citric acid-based (CAB) sanitizer and a conventional quaternary ammonium compound (CQAC) sanitizer were determined against 14 L. monocytogenes isolates at 4-30 degrees C. A subset of isolates (n = 3) was also exposed to sub-lethal concentrations of sanitizers to assess differences in growth behavior. CAB and CQAC were effective at manufacturer recommended concentrations in liquid assays. The MBC of CAB was significantly lower at 4 degrees C compared to 23 degrees C (p < 0.05), whereas the MBC of CQAC was unchanged between 4 degrees C and 23 degrees C. Manufacturers' recommendations for dose and duration of CAB and CQAC were unable to consistently achieve a 5-log reduction of L. monocytogenes attached to surfaces. Findings from this study demonstrate the importance of sanitizer evaluation under conditions representative of their use in the food industry.