Bacterial Variation

The ability of a bacterial culture to manifest more than one set of culture characters is now recognized as a general phenomenon. Since the pioneer studies of Stryker,2" Baerthlein,3 Arkwright,2 and de Kruif6 two or more rather stable culture complexes, which, however, are capable of intertransition in a seemingly orderly manner under certain circumstances, have been described as occurring in many bacterial species. The more commonly observed of these complexes have been designated by the term "culture phase," and the transformation of one phase into another is referred to as "phasic variation" or "bacterial dissociation." The reader is referred to Hadley' 10 for general reviews. The variation pattern of Klebsiella pneumoniae has been the subject of considerable study, as the result of which it is now considered that the phase pattern of this species is composed of at least three culture character complexes.' 6,14,16,17,18 Since these complexes seem analogous to the M (mucoid), S (smooth), and R (rough) culture phases of the pneumococcus,5 these designations have been applied to the corresponding pneumobacillus variants. The variation trend of the pneumobacillus, like that of the pneumococcus, is usually from M to S to R. Transition from the M to the S phase is indicated by a change from the opaque mucoid colony type to the translucent "coli-like" smooth colony type and by the loss of a number of culture characters induding encapsulation, type specificity, the ability to stimulate the production of typespecific antibodies, specific polysaccharide production, and virulence. The S to R phase transformation is indicated by a further change in