Passive protection of NMRI mice against Serratia marcescens: comparative efficacy of commercial human IgG immunoglobulin preparations and rabbit anti-O, -H, -K, -life cell and -protease immune sera.

Three commercial, intravenously applicable human IgG preparations passively protected NMRI mice against intraperitoneal challenge with 11 of 19 selected, serologically defined O-antigen reference strains and clinical, nosocomially significant isolates of Serratia marcescens. Conventional anti-O and anti-H, but not anti-K and anti-protease, rabbit immune sera revealed passive protective capacity against homologous challenge strains; however, anti-O rabbit immune sera failed to invariably protect against heterologous test strains that carried identical serogroup O-antigens. The passive protective efficacy of anti-live cell immune sera, derived from rabbits following recovery from experimental septicemia, was abolished through dual absorption with homologous O-cells. It was concluded that antibodies directed against O-antigens, i.e., lipopolysaccharide moieties, of the challenge strains of S. marcescens afforded passive protection.