Quantitative assessment of hard surface disinfectant activity against the foodborne pathogen Listeria monocytogenes

Listeria monocytogenes is an important foodborne pathogen that must be controlled to ensure food safety. For the years 2003 and 2004, L. monocytogenes caused 20 deaths per 100 listeriosis cases and was responsible for most food recalls for pathogen contamination. The objective of this work was to develop a quantitative method to assess disinfectant activity against L. monocytogenes. Standard procedures for testing disinfectants against 3 bacteria are described in the AOAC Official Methods of Analysis as use-dilution methods. No standard methods are provided for L. monocytogenes. In this study, preliminary efficacy of a quaternary ammonium compound with hydroperoxide ion was determined for 25 bacterial strains. The zones of inhibition ranged from 7.0 to 12.5 mm, and the minimum inhibitory concentration ranged from 5 to 250 ppm. For final efficacy, stainless steel carriers were contaminated with L. monocytogenes and tested separately for 5, 10, and 15 min in disinfectant or phenol. After exposure, the carriers were placed into 2 series of D/E neutralization broth. For 3 replications with duplicate samples, the phenol coefficient was 3.3. This research presents a technique-sensitive method that provides quantitative data for comparison and analysis of disinfectant activity against L. monocytogenes.