Experimental Klebsiella septicemia in mice: treatment with specific antibodies from the rabbit alone and in combination with gentamicin.

Using a model of an experimental Klebsiella pneumoniae septicemia in mice, we examined the therapeutic effect of passively administered specific antibacterial antibodies from rabbits. Both specific IgM and IgG antibody proved to be therapeutically effective. However, the effect of IgG was markedly superior to that of IgM with regard both to the degree of protection and the time interval allowing efficient therapy after infection. The effect of IgG was due to a marked enhancement of in vivo phagocytosis, as demonstrated by monitoring bacterial numbers in the liver, spleen, lungs and kidneys. In mice immunocompromised with cyclophosphamide, treatment with IgG still exerted protection against low challenge inocula. When higher inocula were used, treatment with IgG ceased to influence the final mortality rates but delayed the course of the disease for several days by transient reduction of bacterial numbers in the parenchymal organs. In both normal and immunocompromised mice, concomitant treatment with gentamicin resulted in a marked synergistic enhancement of survival.