Colonial variation in Actinobacillus mallei.

Abstract

An examination of colonies of 51 strains of Actinobacillus mallei grown on a complex agar medium containing heart infusion broth, yeast extract, glucose, and glycerol indicated a high degree of heterogeneity in respect of colonial morphology both within and between strains. A strain possessing high virulence for hamsters (I.P. LD50 for hamsters < 20 cells) was almost completely homogeneous, and colonies of this strain, when viewed microscopically using an oblique lighting technique, were buff in color and had a dull, slightly rough surface and even edges with a slightly cross-hatched appearance. The designation "typical" was given to colonies of this type. Other colonial types designated as "smooth", "intermediate", and "dense, yellow" were isolated from subcultures of this strain. Additional colony types were found upon examination of other strains; these include a "wrinkled variant and several forms of granular and rough colonies. Prolonged incubation of stationary broth cultures of several strains led to the establishment of new colonial types in several strains tested, and ""wrinkled" and "white, opaque, glistening" colonies were isolated from cultures inoculated with "typical" and "intermediate" forms. The relationship of these findings to the earlier work of Mochida is discussed.