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Applied and Environmental Microbiology, February 2008, p. 1111-1116, Vol. 74, No. 4
0099-2240/08/$08.00+0     doi:10.1128/AEM.01292-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Behavior of Bacillus anthracis Strains Sterne and Ames K0610 in Sterile Raw Ground Beef

Microbial Food Safety Research Unit, Eastern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038,¹ Australian Food Safety Centre of Excellence/University of Tasmania, Hobart, Tasmania 7001, Australia,² Microbiology Division, Russell Research Center, Food Safety Inspection Service, Office of Public Health and Science, United States Department of Agriculture, 950 College Station Road, Athens, Georgia 30605,³ Office of Food Defense and Public Health Response, Richard Russell Research Center, Food Safety Inspection Service, United States Department of Agriculture, 950 College Station Road, Athens, Georgia 30605⁴

Received 11 June 2007/ Accepted 23 November 2007

The behavior of Bacillus anthracis Sterne spores in sterile raw ground beef was measured at storage temperatures of 2 to 70°C, encompassing both bacterial growth and death. B. anthracis Sterne was weakly inactivated (–0.003 to –0.014 log₁₀ CFU/h) at storage temperatures of 2 to 16°C and at temperatures greater than and equal to 45°C. Growth was observed from 17 to 44°C. At these intermediate temperatures, B. anthracis Sterne displayed growth patterns with lag, growth, and stationary phases. The lag phase duration decreased with increasing temperature and ranged from approximately 3 to 53 h. The growth rate increased with increasing temperature from 0.011 to 0.496 log₁₀ CFU/h. Maximum population densities (MPDs) ranged from 5.9 to 7.9 log₁₀ CFU/g. In addition, the fate of B. anthracis Ames K0610 was measured at 10, 15, 25, 30, 35, 40, and 70°C to compare its behavior with that of Sterne. There were no significant differences between the Ames and Sterne strains for both growth rate and lag time. However, the Ames strain displayed an MPD that was 1.0 to 1.6 times higher than that of the Sterne strain at 30, 35, and 40°C. Ames K0610 spores were rapidly inactivated at temperatures greater than or equal to 45°C. The inability of B. anthracis to grow between 2 and 16°C, a relatively low growth rate, and inactivation at elevated temperatures would likely reduce the risk for recommended ground-beef handling and preparation procedures.

Published ahead of print on 14 December 2007.