2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Drexel University. Additional details of this research can be found in the report for the parent project 1935-41420-012-00D, entitled Validation of the Effect of Interventions and Processes on Persistence of Pathogens on Foods. Hispanic-style cheese has been associated with both cases and outbreaks of listeriosis. As such, we compared the growth/viability of Listeria monocytogenes in vacuum-packaged slices of commercially-prepared Queso Blanco during storage at temperatures ranging from 5 to 25C. Results revealed that this type of cheese provides a suitable environment for growth of the pathogen at both refrigerated and abuse temperatures. Although there were subtle differences in the duration of the lag phase and growth rate among the 5 temperatures tested, the average maximum population density for all temperatures was about 8.3 log(10) per gram. These findings will be used to estimate growth of listeriae on higher risk foods such as Hispanic-style cheese and to develop appropriate interventions to reduce the potential risk of human illness.