Bacterial Variation in Pneumococcus and Streptococcus Hemolyticus

Arkwright 1 originally described 2 variant forms of members of the colon-typhoid-dysentery group which he designated by the terms S (smooth) and R (rough). Recently evidence has accumulated 2 to show that members of the colon-typhoid-dysentery group, as well as many other bacterial species, possess a third and distinct variant form, the M (mucoid). Organisms in the mucoid phase possess distinct capsules and form large mucoid colonies.

Griffith 3 described 2 variant forms of pneumococcus and, adopting Arkwright's terminology, designated them as S (smooth) and R (rough). A new variant form of pneumococcus was recently described by the author. 4 This new variant form was shown to be strikingly different from the S and R forms described by Griffith.

A comparison of the characteristic features of the 3 chief variant forms of members of the colon-typhoid-dysentery, etc., group on the one hand, and of pneumococcus on the other hand, reveals a striking parallelism. Thus, (1) the M (mucoid) form of the colon-typhoid-dysentery, etc., group corresponds with the S (smooth) form of pneumococcus; (2) the S (smooth) form of the colon-typhoid-dysentery, etc., group corresponds with the R (rough) form of pneumococcus; and (3) the R (rough) form of the colon-typhoid-dysentery group corresponds with the newly described variant form of pneumococcus.

The striking inconsistency in terminology employed to describe corresponding variant forms of different bacterial species is obviously confusing and should be rectified if possible. Before proposing a radical change in the currently accepted terminology of pneumococcal variants a study of bacterial variation in Streptococcus hemolyticus was undertaken in order to determine whether similar variant forms could be demonstrated in this species.