title: Heat activation/shock temperatures for Bacillus anthracis spores and the issue of spore plate counts versus true numbers of spores.
abstract: Assessing true numbers of viable anthrax spores is complex. Optimal heat activation conditions vary with species, media and germinants. Published time/temperature combinations for Bacillus anthracis spores range from 60 degrees C for <or=90 min to boiling for 1 min. Results presented here indicate that temperatures are best kept to <or=70 degrees C and holding times need not exceed 15-30 min. Under conditions of 60 degrees C for 90 min, 62-23 degrees C for 15 min and 70 degrees C for 15 or 30 min, although the ratio of heated:unheated counts ranged from <1 to >1, post-heating counts were less than their pre-heating counterparts on between 71% and 88% of occasions. A high probability was found of viable spore counts differing significantly from counts determined microscopically, with differences of almost 1 log possible. Viable counts were lower than microscopic counts in 15 of 18 tests.
authors.affiliation: Biological Defense Research Directorate, Naval Medical Research Center, Silver Spring, MD 20910-7500, USA. peterturnbull@tesco.net
authors.forename: Peter C B
authors.initials: PC
authors.lastname: Turnbull
authors.forename: Dody A
authors.initials: DA
authors.lastname: Frawley
authors.forename: Robert L
authors.initials: RL
authors.lastname: Bull
mesh_terms: D000881:Anthrax / Q000382:microbiology*; D001408:Bacillus anthracis / Q000502:physiology*; D015169:Colony Count, Microbial; D006358:Hot Temperature; D012189:Retrospective Studies; D013171:Spores, Bacterial / Q000502:physiology