Phase II to phase I conversion of Coxiella burneti in immunosuppressed mice

Coxiella burneti strains 48 and Nine Mile, serologically in phase II, changed their antigenic properties and virulence for guinea pigs and mice upon passaging in immunosuppressed mice. Conversion to phase I of these strains in a system lacking antibody response throws doubt on the importance of specific antibodies in phase variation of C. burneti.