The Transformation of Pneumococcal Types in Vitro.

Abstract

Griffith 1 was the first to show that type-specific, S, pneumococci may be transformed from one specific S type into other specific S types through the intermediate stage of the R form. He showed that the transformation of R forms, derived from one specific S type, into S forms of heterologous types may be effected in vivo by the following procedure: The subcutaneous injection, in white mice, of small amounts of living R forms together with suspensions of heterologous S cultures, killed by heating. Griffith further reported that all attempts to secure transformation of type by in vitro methods were unsuccessful.

Griffith's observations were confirmed and extended in recent publications by one of the authors. 2 In these communications it was also reported that all in vitro attempts to effect transformation of type were unsuccessful.

Recently we have renewed the in vitro studies and have succeeded in evolving a relatively simple technique for inducing transformation of pneumococcal types in the test tube.

For the purposes of convenience we have confined our present studies to the transformation of a 2R culture into Type III S organisms. However, since it has been shown in previous work that an R culture may be transformed in vivo into S organisms of any heterologous type it is probable that similar transformations may also be effected in vitro.

The procedure consists in seeding minimal amounts of an R culture into a suspension of S organisms of heterologous type, killed by heating. Certain conditions, while not absolutely necessary, apparently facilitate the transformation process. Some of these conditions are : (1) The amount of the R inoculum introduced, (2) the incubation of the cultures for a longer time than the conventional period, (3) the addition of a small amount (10%) of anti-R serum, (4) the addition of a small amount of blood-broth.