Serotyping of Chlamydia. I. Isolates of ovine origin

8 chlamydial isolates of ovine origin were tested in a plaque reduction system using homologous and heterologous rooster antisera. The 8 isolates could be separated into 2 separate immunotypes. Type 1 included isolates associated with ovine abortion and one agent recovered from the feces of an apparently normal sheep. Type 2 isolates were associated with polyarthritis and conjunctivitis. These 2 serotypes were not cross reactive with several chlamydiae of avian origin. Further application of the plaque reduction test may provide a useful means of typing chlamydiae.