Dissociation of Pneumococcus

Abstract

I. A New Colony Variant of Pneumococcus. R colonies of pneumococcus, suitably spaced on blood agar, are allowed to age for 6 to 7 days at 37°C. Under these conditions many of the colonies give rise to a variety of secondary growths including daughter colonies, peripheral excrescences and a peculiar form of localized, marginal outgrowth with a rough, fungoid appearance. These various forms of secondary growth have been observed in some detail and the rough, localized, marginal outgrowth represents an unusual phase of development. When transfers are made from such areas to fresh blood agar plates a new type of colony is produced. Its appearance varies considerably with age, but at all periods of growth is characteristically different from the parent colony. Young colonies (4-8 hours) present an extremely rough and irregular surface with delicate, filamentous edges. With age the surface is coarsely rough with an irregular fimbriated border. At 12-16 hours the surface is slightly convex, but after 24 hours the colonies become flattened. They continue to show an irregular margin and are approximately twice the diameter of the parent R colonies grown under similar conditions. With further ageing the colonies develop an extraordinary, spreading, filamentous type of marginal growth.

Stained smears of such colonies show an unusual morphological picture, varying with age, but quite distinctive at all periods of growth. The bacteria consist mostly of plump cocci and cocco-bacilli arranged in long chains. In younger colonies the organisms are almost exclusively Gram positive, but in the older ones there is considerable variation in staining properties. In addition to the plump coccal and cocco-bacillary forms, large numbers of granular elements of various sizes are present,

The stages in the development of the marginal outgrowth which produces the new type of colony have been carefully studied.