Thermal inactivation of Bacillus anthracis Sterne in irradiated ground beef heated in a water bath or cooked on commercial grills ☆ Vijay K. Juneja a, ⁎, Anna C.S. Porto-Fett a , Jeffrey E. Call a , Harry B. Marks b , Mark L. Tamplin c , John B. Luchansky a a U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Microbial Food Safety Research Unit, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA b U.S. Department of Agriculture, Food Safety and Inspection Service, 14th and Independence S.W., Washington, DC 20250, USA c Tasmanian Institute of Agricultural Research, School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tasmania, 7001, Australia abstract article info Article history: Received 18 March 2009 Accepted 17 August 2009 Editor Proof Receive Date 5 September 2009 Keywords: Bacillus anthracis Ground beef Pathogen Biosecurity Food safety The thermal stability of heat-shocked and non-heat-shocked spores of the virulence-attenuated Sterne strain of Bacillus anthracis was evaluated at select temperatures in irradiated, raw ground beef (25% fat) heated in a water bath or cooked using two different commercial grills. For the former, 3-g portions of inoculated ground beef were packaged in bags that were completely immersed in a temperature-controlled circulating water bath held at 65 °C (149 °F), 70 °C (158 °F), 75°(167 °F), and 80 °C (176 °F) for a predetermined length of time. For the latter, formed ground beef patties (95-g each) were inoculated with spore stock A or B of the Sterne strain and then cooked on a commercial open-flame gas grill or on a commercial clamshell electric grill to achieve target internal temperatures of either 71.1 °C (160 °F), 82.2 °C (180 °F), or 93.3 °C (200 °F). Cooking ground beef patties on commercial grills, resulted in reductions of ca. 0.8 to 3.5 log 10 CFU/g for spore stocks A and B of B. anthracis Sterne after heating to 71.1 °C (160 °F), 82.2 °C (180 °F), or 93.3 °C (200 °F) on either the open-flame gas grill which required ca. 9.6 min to reach the target internal temperatures or on the clamshell electric grill which required ca. 4.0 min to reach the target internal temperatures. In comparison, our data using a water bath system and heating at 65° to 80 °C predict nearly 4 log reductions in spore levels for short times, ~½ min, depending possibly on the temperature. Thus, our data suggest that models based on heating ground beef in a water bath is not a good predictor of reductions of levels of spores of B. anthracis Sterne strain that would be obtained when cooking ground beef patties on commercial grills under conditions that may be typically used by consumers and/or retail establishments. Nevertheless, our data validated that cooking ground beef patties on a commercial grill at a temperature considered to be “well- done” and a temperature (71.1 °C;160 °F) recommended by the USDA/FSIS, is effective at killing spores of B. anthracis Sterne. Industrial relevance: Heating ground beef in a water bath or cooking ground beef patties on commercial grills under conditions simulating those that are used by consumers and/or that occur in retail food service establishments is effective at killing spores of B. anthracis Sterne. Published by Elsevier Ltd 1. Introduction Bacillus anthracis causes a disease known as anthrax, which is an often fatal bacterial infection that occurs when spores enter the body through abrasions in the skin or by inhalation or ingestion. Thus, the disease could be of the cutaneous, inhalation, or gastrointestinal forms (Friedlander, 1999). Symptoms of gastrointestinal infection or food- borne anthrax include nausea, fever, abdominal pain, diarrhea, ulceration, hemorrhage, edema, and ascites, as well as an eventual fluid shift from the vascular compartment leading to shock and death of an individual within 2 to 3 days following consumption of a contam- inated food (Sirisanthana & Brown, 2002). Therefore, contamination of food with B. anthracis, although rare, is a potentially significant public health hazard. Since the American food chain relies on a centralized production and processing system for an ever-increasing and widespread distribution of food products (Sobel, Khan, & Swerdlow, 2002), our food supply is particularly vulnerable to deliberate contamination with threat agents. Although the incidence of B. anthracis in foods is rare and although medical advances have decreased its importance for both livestock and humans (Smith et al., 2001), following the October 2001 incident of terrorism involving the purposeful addition of B. anthracis spores to mail, this pathogen has been identified as a potential biological weapon that could be used by terrorists. An intentional contamination of food Innovative Food Science and Emerging Technologies 11 (2010) 123–129 ☆ Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. ⁎ Corresponding author. Tel.: +1 215 233 6500; fax: +1 215 233 6581. E-mail address: vijay.juneja@ars.usda.gov (V.K. Juneja). 1466-8564/$ – see front matter. Published by Elsevier Ltd doi:10.1016/j.ifset.2009.08.011 Contents lists available at ScienceDirect Innovative Food Science and Emerging Technologies journal homepage: www.elsevier.com/locate/ifset