Hamster challenge potency assay for evaluation of Mycoplasma pneumoniae vaccines

A hamster immunization challenge assay described in the accompanying paper (M. F. Barile, D. K. F. Chandler, H. Yoshida, M. W. Grabowski, R. Harasawa, and S. Razin, Infect. Immun. 56:2443-2449, 1988) was used to examine protection against Mycoplasma pneumoniae disease by passive immunization and to evaluate the protective potency of a Formalin-inactivated whole-cell and a cell extract M. pneumoniae vaccine. Passive immunization with a globulin fraction of hyperimmune mule antiserum to M. pneumoniae provided hamsters some protection against the challenge. When hamsters were actively immunized, a single dose of Formalin-inactivated vaccine provided only minimal protection, whereas multiple doses of this vaccine, particularly when combined with adjuvant, provided good protection. A single dose of the cell extract vaccine did not protect animals, but two doses caused a marked reduction of disease when a priming dose was given intraperitoneally, followed by a booster dose intratracheally. The correlation between the level of metabolism inhibition antibodies to M. pneumoniae in the sera of vaccinated hamsters and the degree of protection as measured by reduction of lung pathological scores and colonization was poor, indicating that seroconversion rates for metabolism inhibition antibodies are not by themselves adequate to measure the potency of M. pneumoniae vaccines.