Identification of capsular antigens in Serratia marcescens

Previous studies with 31 strains of Serratia marcescens, including 28 reference O-serotype strains, have indicated that 19 of them have an acidic polysaccharide which copurifies with lipopolysaccharide during phenol-water extraction. Polysaccharide in crude extracts from 18 of the 19 strains was precipitated with Cetavlon (hexadecyltrimethyl ammonium bromide), and capsules were demonstrated around these 18 strains by Indian ink exclusion zones. Capsule-antibody binding by the Quellung reaction suggested that the acidic polysaccharide formed the capsule around the bacterial cells. Anticapsular (anti-K) antibody was detected in reference O antisera which had been prepared against boiled whole cells. Cross-titration and absorption studies revealed 14 different K antigens among these strains.