Identification of a subspecies-specific capsular antigen from Bacteroides melaninogenicus subspecies asaccharolyticus by immunofluorescence and electron microscopy.

An indirect fluorescent antibody test was developed with the use of hyperimmune rabbit antiserum to a purified capsular polysaccharide of Bacteroides melaninogenicus subspecies asaccharolyticus. All of 23 strains of B. melaninogenicus subspecies asaccharolyticus were fluorescence-positive in this test. All 11 strains of Bacteroides melaninogenicus subspecies intermedius tested and three strains of Bacteroides melaninogenicus subspecies melaninogenicus were fluorescence-negative. Thirty-one strains of other bacterial species were also fluorescence-negative. The indirect fluorescent antibody test demonstrated the presence of a subspecies-specific capsular antigen from B. melaninogenicus subspecies asaccharolyticus. The capsular antigen was further demonstrated by electron microscopy with ruthenium red, a polysaccharide-staining material.