On the Differentiation of Anthrax Bacilli from Bacillus Cereus

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Abstract
It has been suggested by other investigators that Bacillus anthracis is properly to be regarded as a mere variant of B. cereus and that transitional forms exist preventing a satisfactory differentiation into separate species. Evidence to the contrary is presented, confirming earlier observations, demonstrating that pure strains of B. anthracis which have partially or wholly lost their virulence remain identifiable as anthrax bacilli, and can still be clearly differentiated from B. cereus. New experiments have confirmed an earlier conclusion that the illness produced by injecting animals with rapidly multiplying pure cultures of B. cereus is an experimental disease due to an independent pathogenicity of these strains, and is unrelated to anthrax disease. Animals immunized to anthrax have been shown to remain susceptible to infection by B. cereus. A study of the behavior od deliberately prepared mixtures of B. anthracis and B. cereus has demonstrated that the distinctive characteristics of the two organisms are maintained in these mixed cultures. The multiplication of B. anthracis is suppressed in vitro, but not in vivo. Since such mixed cultures can appear accidentally in any culture collection, and since the marked similarity of the two bacilli may allow the contamination to go undetected for long periods, it seems likely that the inadvertent use of such mixed growths may account for some of the otherwise inexplicable observations in the literature. A review of available differential tests gives B. anthracis a secure place as a valid species in its own right.