Quantitative Assay for Crude Anthrax Toxins

Haines, Bertram W. (U.S. Army Biological Laboratories, Frederick, Md.),Frederick Klein, and Ralph E. Lincoln . Quantitative assay for crude anthrax toxins. J. Bacteriol.89: 74–83. 1965.—The whole crude toxins ofBacillus anthracis , although apparently responsible for the death of animals with anthrax, had never been quantitated. A total of 14 lots of the toxic culture filtrate ofB. anthracis were pooled into one large lot of crude anthrax toxins. An extensive assay of this reference material was conducted in four laboratories by use of the time-to-death of the intravenously challenged Fischer 344 rat as the response variable. Doses of the material were varied factorially by concentration, dilution, and volume. The data from this study were used to define a potency unit of the crude anthrax toxins. Procedures were developed and illustrated for the assay of unknown lots of the toxins by comparing the rat time-to-death response to the unknown with either (i) the responses reported in this study, or (ii) directly with the rat responses to a new sample of the reference toxins. The possibilities and limitations of this standardization and of the statistical procedure through which it was developed are discussed.