1. Food and Feed Safety Research Unit, Southern Regional Research Center, U.S. Department of Agriculture, New Orleans, Louisiana, 70124
2. Division of Virulence Assessment, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, Maryland, 20708
3. Division of Molecular Biology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, Maryland, 20708