The Structure of B. Anthracis and the Reversal of the Gram Reaction.

Abstract

If a small amount of aqueous solution of acriviolet (1 oeseful of a 1 per cent solution) be added to ½ cc. of a heavy aqueous suspension of B. anthracis it will be found that the organisms are changed by the exposure from sharply Gram positive to sharply Gram negative.∗ The speed with which this change takes place varies with the strain. In one of the 7 strains examined the change was complete in 2 hours. In other strains it was complete only at the end of 19 hours. Exposure to gentian violet gave results similar to those obtained with acriviolet.

The Gram negative forms present after exposure to these dyes are notably smaller in caliber than the Gram positive forms. Measurements of the stained specimens with a filar micrometer show the loss of caliber to be on the average in the neighborhood of 25 per cent. This measured difference in size in the stained specimens is probably in part due to the piling up of stain on the Gram positive segments since the difference in size, though demonstrable in unstained hanging drop specimens, is of lesser degree than in the stained specimens.

The change in Gram reaction and the change in size cause a striking picture in smears, stained by Gram's method, made from suspensions to which dye has ken added, and which are examined at a period when the changes produced are as yet only partial. Chains of bacteria are seen in which stout, deeply Gram positive segments alternate with slender, sharply Gram negative segments. When individual bacteria are present instead of chains, the picture is that of a smear of two different organisms, one stout and Gram positive, the other slender and Gram negative.