Abstract
Numerous observations on bacterial dissociation indicate that the changes occurring as a result of dissociation may involve many of the cultural characteristics. Although alterations in colonial morphology are the most obvious, many other characteristics may also undergo modification. De Kruif demonstrated changes in virulence 1 and acid agglutination optimum. 2 Profound serological alterations have been studied by Arkwright, 3 Schütze, 4 Savage and White, 5 Goyle. 6 The modifying effects of dissociation on many biochemical reactions, including fermentative capacities, have also been reported. 7 In a recent study of the fermentations of variants of Salmonella schottmülleri, Nungester and Jung 8 obtained R-variants which formed gas and others that did not; they observed that an S-culture may lose its capacity to form gas without change in colonial morphology. These observations, they concluded, were in accord with the concept of independent variation of bacterial properties.
Our studies on S- and R-variants of Salmonella schottmülleri, Salmonella morgani and Shigella paradysenteriae (Flexner) appear to demonstrate that many of the biological characters—serological, morphological and physiological—of these cultures are capable of independent variation during the dissociative and revertive processes.
Well-stabilized R-variants were obtained from the 3 normal S-cultures by growth in formalin (1:8000) beef infusion broth. Each of the R-cultures regularly produced 100% rough colonies on agar plates. The R-variants were then subjected to environmental conditions favoring reversion: (1) growth in 2% homologous immune serum broth; (2) growth in broth containing 2% vaccine prepared by heating an 18-hour growth of the original smooth culture for 4 hours at 56°C.; (3) rapid transfers in plain beef infusion broth. A variety of “reversion ”cultures, derived from the 3 R-variants, was obtained.
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