Antibody response to Serratia marcescens isolated from patients with malignant diseases

Sixty-four patients with malignant diseases from whom Serratia marcescens was isolated from various sources were studied regarding their antibody responses to somatic O antigens of this microorganism. Antibodies were titrated by the passive hemagglutination test. An antibody response was considered present when either a fourfold or greater rise in antibody titers between two consecutive serum specimens was demonstrated, or when elevated titers (greater than or equal to 40 for serogroup O14 and greater than or equal to 160 for all others) were present in the first available specimen. Overall, 31% of subjects mounted an immune response, but there were differences depending upon the infection site. Seventy-one percent of patients with S. marcescens bacteremia responded immunologically; whereas the percentage for patients with Serratia present in the respiratory tract was only 22%, in the urinary tract, 31%, and in wounds, 26%. Documentation of an immune response to the patient's own infecting strain of Serratia aids in the differentiation between infection and contamination and possibly also between clinical disease and colonization. In addition, immunoglobulin samples collected in different decades were examined to determine whether the background level of antibodies to S. marcescens had changed in the general population over the years. No difference in antibody titers to 13 O antigens was observed in immunoglobulin preparations from 1951, 1962, 1971, and 1975.