Studies on Pneumococcus Variation: II. Smooth Virulent Variants Produced by Daughter-Colony Dissociation of Smooth Pneumococcus Strains.

A previous paper (Eaton, 1934) described variants of the pneumococcus characterized by a tendency to undergo rapid spontaneous lysis under certain cultural conditions at 370C. These variants were produced by daughter-colony dissociation of smooth pneumococcus strains on blood agar at 250C. A further investigation of this method of dissociation revealed that a second and independent type of variation is also produced by the formation of daughter colonies. This consisted in the appearance of a stable smooth variant in the daughter colonies. The purpose of this paper is to demonstrate that dissociants obtained from the daughter colonies which first appear at 250C. on the colonies of S pneumococci are smooth strains distinguishable in colony form and other characteristics from the parent smooth strains. The production of these variant S forms has been observed with great regularity in the daughter colony dissociation of most of the pneumococcus cultures of types I, II, III and group IV so far studied. Daughter-colony formation occurs with especial ease in recently isolated strains. Hadley (1927) has pointed out the frequency of daughtercolony formation in many species of bacteria. He believes that the dissociants formed in daughter colonies are usually not true rough variants. Sometimes these dissociants form large smooth mucoid colonies on subculture, as with organisms of the typhoid