Further studies of the phenomenon of capsular swelling of Micrococcus pyogenes var. aureus in the presence of immune serum.

In 1954 we (Price and Kneeland) described a mucoid form of Micrococcus pyogenes var. aureus (Staphylococcus aureus) which showed capsular swelling with homologous immune serum. This mucoid variant, designated RL-mucoid, was derived from the parent RL strain after passage through embryonated eggs with influenza virus. Attempts to reproduce this variation by passing RL through embryonated eggs on subsequent occasions were unsuccessful. The original RLmucoid variant, however, could be maintained indefinitely on subculture, provided that an occasional egg passage was performed if the strain appeared to be losing its mucoid character. RL-mucoid and RL were found to be mannitoland coagulase-positive, to have similar virulence for mice, and identical phage typing. Apart from the differences in colonial morphology, the two strains could only be distinguished by their capacity to show capsular swelling, and by their capacity to produce potent antisera. In other words, anti-RL-mucoid serum produced rapid and complete capsular swelling of RLmucoid orgais, whereas only an occasional RL organism would be so affected. Similarly, anti-RL serum caused relatively slight capsular swelling of RL-mucoid organisms, and none of the RL organisms. It was thought that the difference between RL-mucoid and RL was a quantitative one, and related to the amount of capsular substance produced. In the discussion it was stated that "the serological specificity of this reaction remains to be determined, since we have not had the opportunity to study the capsular substance from a variety of different strains of staphylococci to find out if they are antigenically distinct. If this should be the case, it would create a new method for serological classification." The present communication presents data relating to 39 other strains, and indicates that the reaction is not type-specific. METHODS AMD MATERIALS