Dissociation of B. Anthracis.

Abstract

Occasional reports of atypical anthrax colonies have been made. These include such observations as those of Preisz, 1 , 2 Markoff, 3 Wagner, 4 Gratia, 5 etc. Varying significance has been attached to such atypical forms. Preisz noted these peculiar colonies in vaccine cultures and believed them to be contaminations. After reproducing these colony forms from pure line cultures weakened by growth in broth at 42.5° C., he concluded that they were variants arising from the “weakened” culture. Other workers have generally referred to these modifications merely as variations. Markoff stressed the external environment as influencing variation. Wagner suggested a possible analogy between his “teratologische forms” and the “sogenannten Q-Formen in der Typhus-Coli Gruppe.”

In the spring of 1926 we obtained, by plating from broth, a dissociation of an apparently “normal” laboratory stock culture of B. anthracis (maintained continuously in the laboratory since 1888) into two colonial types: one was the usual flat, dull anthrax colony, the other a small, round, slightly rough colony. The latter resembled the “B” colony described by Wagner. This dissociation has been repeated on the stock culture purified by over 50 successive single colony isolations.

As a result of thew findings we became interested in the behavior of the anthrax bacillus in the light of the modern views 011 microbic dissociation 6 . Should we consider such atypical colonies as having split from the parent culture and having remained as rather fixed variants? Or was there a closer genetic relationship?