THE BEHAVIOR OF BACILLUS ANTHRACIS STRAINS STERNE (AVIRULENT) AND AMES K01610 (VIRULENT) IN STERILE RAW GOUND BEEF

Authors: Tamplin, Mark; Stewart, Tod; PHILLIPS, ROBERT - FSIS; Luchansky, John; KELLEY, LYNDA - FSIS

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2007
Publication Date: 2/1/2008
Citation: Tamplin, M.L., Stewart, T.E., Phillips, R., Luchansky, J.B., Kelley, L. 2008. The behavior of bacillus anthracis strains sterne (avirulent) and ames k01610 (virulent) in sterile raw gound beef. Applied and Environmental Microbiology. 74:1111-1116.

Interpretive Summary: Since the terrorist attacks of 2001, the U.S. government has recognized that the food supply may be vulnerable to attack with biological agents not usually considered threats to the food supply. Bacillus anthracis is an atypical foodborne pathogen with a high level of interest as a threat agent. This spore-forming bacterium has already been used in one terrorist attack and is considered to be a bioterrorism and biowarfare agent against civilian populations. While many studies have determined the viability of B. anthracis spores after exposure to different environmental conditions such as freezing, heating, drying and changes in pH, these studies are most often carried out in laboratory media or buffers and may not accurately represent a pathogen's behavior in retail food. The behavior of B. anthracis Sterne, a non-pathogenic strain, was measured in sterile raw ground beef from 2 degrees (36 degrees F) to 70 degrees C (158 degrees F). The strain died at a slow rate from 2 degrees (36 degrees F) to 16 degrees C (61 degrees F) and was rapidly killed at temperatures greater than or equal to 45 degrees C (113 degrees F). Growth was observed from 17 degrees (63 degrees F) to 44 degrees C (111 degrees F). At these permissive temperatures, the time for the cells to initiate growth decreased with increasing temperature, and growth rate increased with increasing temperature. Interestingly, B. anthracis did not grow well in ground beef compared to common foodborne pathogens. A pathogenic strain of B. anthracis, Ames K0610, showed similar growth and death patterns as the Sterne strain, with the exception that it did not reach the same population densities as the Sterne strain at 30 degrees (86 degrees F), 35 degrees (95 degrees F) and 40 degrees C (104 degrees F). B. anthracis Ames K0610 spores also rapidly died at temperatures greater than and equal to 45 degrees C (113 degrees F).

Technical Abstract: The behavior of Bacillus anthracis Sterne spores, encompassing bacterial growth and death, was measured in sterile raw ground beef at storage temperatures, 2 degrees to 70 degrees C. Bacillus anthracis Sterne was killed at a slow rate of -0.003 to -0.014 log10 cfu/h at storage temperatures of 2 degrees to 16 degrees C, and at temperatures greater than and equal to 45 degrees C. Growth was observed from 17 degrees to 44 degrees C. At these intermediate temperatures, B. anthracis Sterne displayed the typical growth patterns of lag, growth and stationary phases. Lag phase duration decreased with increasing temperature, and ranged from approximately 53 to 3 hours. Growth rate increased with increasing temperature from 0.011 to 0.496 log10 cfu/h. Maximum population densities (MPD) for B. anthracis Sterne ranged from 5.9 to 7.9 log10 cfu/g. The fate of B. anthracis Ames K0610 was measured at 10 degrees, 15 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees and 70 degrees C to compare its behavior with Sterne. There were no significant differences between the Ames and Sterne strains for growth rate and lag time. However, the Ames strain displayed a MPD that was 1.0 to 1.6 times higher than the Sterne strain at 30 degrees, 35 degrees and 40 degrees C. B. anthracis Ames K0610 spores were rapidly killed at temperatures greater than or equal to 45 degrees C.