Spores of Bacillus anthracis are known to be extremely resistant to heat treatment, irradiation, desiccation, and disinfectants. To determine inactivation kinetics of spores by high pressure, B. anthracis spores of a Sterne strain-derived mutant deficient in the production of the toxin components (strain RP42) were exposed to pressures ranging from 280 to 500 MPa for 10 min to 6 h, combined with temperatures ranging from 20 to 75°C. The combination of heat and pressure resulted in complete destruction of B. anthracis spores, with a D value (exposure time for 90% inactivation of the spore population) of approximately 4 min after pressurization at 500 MPa and 75°C, compared to 160 min at 500 MPa and 20°C and 348 min at atmospheric pressure (0.1 MPa) and 75°C. The use of high pressure for spore inactivation represents a considerable improvement over other available methods of spore inactivation and could be of interest for antigenic spore preparation.Bacillus anthracis is a spore-forming gram-positive bacillus that causes anthrax. This zoonosis mostly affects herbivores. Occasionally humans contract the disease via the cutaneous route or via inhalation of aerosolized spores. The risk of biological warfare and bioterrorism is of increasing concern for governmental authorities, especially since the dissemination of spores through letters sent through the postal system. This caused 22 cases of human anthrax, with 5 fatal cases of inhalation anthrax (5). Consequently, research on anthrax prophylaxis and decontamination has been intensified. In this context, improved anthrax vaccine efficiency and spore inactivation methods are needed for safe antigenic preparation (2).Bacterial spores can survive in the environment for an extraordinarily long time; they are in a dormant state and resist physical and chemical stress. Several techniques, alone or combined, have already been tested for the inactivation of Bacillus spores: heat, acid pHs, nisin, ultrasonic waves, irradiation, and high pressure (4,11,17). High-pressure technology has been used since 1990 in the food industry for preservation and food processing. High hydrostatic pressure has proven to be efficient for destruction of vegetative bacteria, viruses, and yeasts, with bacterial spores being more resistant to pressure (6, 9). Due to a renewed interest in methods of B. anthracis spore inactivation, UV resistance was recently revisited (10), but high hydrostatic pressure had never been applied to the inactivation of B. anthracis spores. The aim of this study was to evaluate the efficacy of high-pressure treatment, alone and in association with heat, on the inactivation of spores of B. anthracis strain RP42, derived from the Sterne strain. B. anthracis Sterne is an attenuated nonencapsulated variant. This strain does not have the pXO2 plasmid, which carries the capsule genes of the vegetative bacterium. The RP42 strain contains the pXO1 plasmid from which the genes for edema factor and lethal factor production were deleted. This avirulent strain is a valuable model f...
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