Abstract
A cross-reaction between Acinetobacter calcoaceticus and chlamydiae is described. A water-soluble, heat stable, non-dialyzable antigen was extracted from Acinetobacter species by boiling. This antigen fixed complement in the presence of homologous hyperimmune sera from rabbits or guinea pigs and in the presence of heterologous human or hyperimmunized animal sera containing chlamydial antibodies. Hyperimmune antisera to the extracted antigen, or to suspensions of live acinetobacters, also reacted in complement fixation with a group-specific antigen.