On the occurrence of serum antibodies to Bacteroides fragilis and serogroups of E. coli in patients with Crohn's disease.

Eight strains of Bacteroides fragilis, five isolated from patients with Crohn's disease and three from healthy individuals, and according to biochemical tests belonging to four subspecies, were subjected to a serologic examination with tube agglutination and passive hemagglutination (HA) tests using hyperimmune rabbit antisera. A close antigenic relationship was demonstrated between two of the strains and minor relationships between three other strains. Cross absorption experiments showed that the antigenically related strains had common antigen(s) besides strain specific antigens. Crude antigens of each of the eight B. fragilis strains, and eight known serotypes of nonenteropathic E. coli, were used in passive HA tests to study the occurrence of circulating hemagglutinins in patients with Crohn's disease, and in control patients and healthy individuals with no obvious intestinal disease. It was found that patients with Crohn's disease had higher titres against B. fragilis than control patients and healthy individuals (the p-value was less than 0.01 if titres greater than or equal to 1:40 were chosen as comparison, equal for males and females). Higher titres were also recorded for Crohn's patients against the various serotypes of E. coli than for control patients and healthy individuals (if titres less than or equal to 1:160 were chosen as comparison the p-value was less than 0.01 for men and less than 0.001 for women.