Detection of specific IgG antibody in sera from patients infected with Bacteroides fragilis by enzyme-linked immunosorbent assay.

During a period of 13 months, 28 serious infections caused by Bacteroides were seen in 27 patients. Sixteen patients yielded Bacteroides fragilis; sera from 13 (81%) of these 16 had increased levels of IgG specific for B. fragilis lipopolysaccharide (LPS) antigens by enzyme-linked immunosorbent assay (ELISA). Sera from 20 normal controls did not have increased specific IgG. Sera from 22 of 23 patients with bacteremia caused by other gram-negative rods also failed to yield increased levels of specific antibody (P less than 0.0012). Analysis of sera from patients with B. fragilis infections disclosed a significant correlation between the levels of specific IgG to B. fragilis LPS measured by ELISA and the IgG antibody to the infecting B. fragilis by indirect immunofluorescence (r = 0.84, P less than 0.012). Two of the remaining 12 infections caused by Bacteroides not apparently due to B. fragilis organisms were also associated with increased levels of specific IgG to B. fragilis LPS antigens. Specific IgG antibody response may be an important adjunct in diagnosis of common B. fragilis infections and may allow better management of antimicrobial agents.