Transformation of Pneumococcal Types

Abstract

GRIFFITH¹ was the first to show that an attenuated and non-encapsulated 'rough' (R) variant of one specific type of Pneumococcus could be transformed into a virulent and encapsulated 'smooth' (S) form of another specific type. The transformation was accomplished in vivo by injecting subcutaneously a small amount of living R culture of Pneumococcus Type II together with a relatively large inoculum of heat-killed organisms derived from a fully virulent S strain of Pneumococcus Type I or III. The living R strain alone failed to kill mice, whereas the addition of the heat-killed Type I or III organism caused a fatal bacteriæmia. The organism isolated from the heart's blood of the infected animals, however, was not a virulent Type II organism, but a virulent encapsulated Type I or III pneumococcus according to the type of the heat-killed S vaccine employed. The importance of this observation was soon recognized, and Griffith's findings were confirmed by Neufeld and Levinthal², Baurhenn³ and Dawson⁴. Some time later, Dawson and Sia⁵ succeeded in carrying out the transformation of R Type II pneumococci into a virulent S Type III organism by an in tivro procedure.