STUDIES ON THE VARIATION OF BACTERIUM TULARENSE

Abstract

The recognition of colony type variants of B. tularense has been made possible by the use of an oblique lighting technic in the examination of colonies on transparent agar medium. Changes in virulence and immunogenic properties of B. tularense are frequently associated with an alteration of colony types. Changes in these properties are most frequently observed following prolonged incubation in liquid media and can be attributed to the progressive establishment of spontaneously arising variants (mutants) in growing cultures under conditions that are more favorable for the variant type than for the parent type. The type and composition of the medium, the initial pH, and the inoculum size affect population changes, and one or more factors present in old culture filtrates appear to play an important role in the creation of environmental conditions that lead to population changes. Correlations have been made between the acriflavine reaction, acid agglutination, virulence, immunogenic potency, and the morphology of various colony types isolated from a variety of B.tularense cultures. A demonstration of considerable heterogeneity in what had been assumed to be pure stock cultures and the recognition of variation in important characteristics emphasize the importance of using clones and of controlling the factors that cause population changes in exptl. studies with B. tularense. Without recognition of these factors, certain cultures may be assumed to possess innate differences in virulence (or immunogenic properties), whereas they may merely represent related heterogeneous populations containing different proportions of highly virulent and weakly virulent types.