Specific and Nonspecific immunity to Serratia marcescens infection

By specific active or passive immunization, mice were protected against lethal infection with Serratia marcescens. Animals that were immunized against organisms of the challenge strain O serotype survived, whereas animals that were immunized against other serratia O serotypes did not survive. Protective sera (from convalescent partients or immunized rabbits) contained a specific complement-independent opsonin. These sera also contained passive hemagglutinating and bacterial agglutinating antibodies in high titer. The protective and complement-independent opsonizing antibodies were associated with IgG fractions of the serum, while the agglutinating antibodies were primarily associated with the IgM. Mice also survived infection with Serratia after immunization against the Re595 Salmonella minnesota mutant. However, complement-independent opsonizing antibody was not demonstrated in these cross-protective sera.