2007 Annual Report 1a.Objectives (from AD-416) The goal of this cooperative research project is to determine the molecular basis for the development of sanitizer tolerance in Listeria monocytogenes. One objective this research is to determine gene expression differences in planktonic and biofilm Listeria monocytogenes subjected to oxidative and quaternary ammonium sanitizer stresses. A second objective is to assess the contribution of genes up-regulated in response to oxidative and quaternary ammonium stress to biofilm formation and stress tolerance. 1b.Approach (from AD-416) Gene expression information for two strains of L. monocytogenes will be obtained by microarray hybridization analyses of mRNA from the following cell types: Untreated planktonic cells Untreated biofilm cells Biofilm cells treated with hydrogen peroxide Biofilm cells treated with QAC Planktonic cells treated with hydrogen peroxide Planktonic cells treated with QAC Gene expression comparisons will include: Planktonic versus biofilm cells Planktonic cells before versus after hydrogen peroxide exposure Planktonic cells before versus after QAC exposure Biofilm cells before versus after hydrogen peroxide exposure Biofilm cells before versus after QAC exposure The role of genes will be confirmed by constructing specific mutations of genes indicated by microarray analysis and determining the phenotype of the mutants. 3.Progress Report This report serves to document research conducted under a specific cooperative agreement between ARS and the Universityof Georgia, Department of Food Science. Additional details of the research can be found in the report for the parent in-house CRIS project 6612-41420-015-00D, Microbial Ecology of human Pathogens Relative to Poultry Processing. Listeria monocytogenes is a pathogen that can have serious consequences on the health of an infected person. The pathogen is commonly passed to humans by food that has become contaminated in processing or post-processing. L. monocytogenes is difficult to eliminate because it forms biofilms that are resistant to sanitation procedures. The purpose of this project is to determine which genes are responsible for L. monocytogenes formation of biofilms and which are responsible for the increased resistance to sanitation. Biofilm-grown and free-living Listeria cells were exposed to pulses of hydrogen peroxide and messenger RNA was recovered from these and control cells. The experiments were repeated three times and the RNA was sent to Dr. Chris Minion of Iowa State University to be processed for hybridization array analyses. To date the first replication has been processed but the data has not yet been interpreted. Ultimately, we will be able to understand the mechanisms used by L. monocytogenes for residence in a processing plant and we will be able to created intervention procedures. MONITORING: The ADODR has had regular face-to-face, email and telephone conversations with the cooperator at the University of Georgia on research planning and carrying out the research.