Human serum bactericidal activity against Serratia marcescens: failure of human, "natural," specific anti-O IgG antibodies to enhance serum bactericidal activity.

A commercial, low pH-derived, intravenously applicable human IgG immunoglobulin preparation (Sandoglobulin) revealed O-agglutinin activity against 16 of the 21 O-antigens of Serratia marcescens, although at low titers; this IgG preparation lacked H-immobilizing antibodies against this microorganism. The bactericidal activity of 65 vol% of normal, fresh human serum was neither enhanced nor significantly antagonized following addition of 25 vol% of undiluted or 1:4 diluted. Sandoglobulin, as determined with test strains of S. marcescens that represented various human serum susceptibility categories. This indifferent effect was obtained despite documented O-agglutinin activity directed against several of the assay strains. It was concluded tentatively, that human, "natural" anti- S. marcescens IgG antibodies failed to augment human serum bactericidal activity in vitro against this opportunistic-pathogenic microorganism.