Sucrose density differences of Chlamydia psittaci 6BC in relation to its host

Previous studies on Chlamydia psittaci 6BC propagated in different hosts have shown differences in cytotoxicity but no differences in the ultrastructure of the individual particles. It is shown here that the 6BC strain derived from yolk sac of infected chick embryo sedimented in sucrose gradients at lower densities than the 6BC strain derived from L-cells. Host-related modifications of lipid concentrations of the 6BC strains have been previously documented by others. It is thought that the phenomenon of host-induced modifications of physical properties of the agent might provide a new approach to the study of chlamydial pathogenicity.