Correlation of an expanded direct fluorescent-antibody system with an established passive hemagglutination system for serogrouping strains of Campylobacter jejuni and Campylobacter coli

Rabbits were inoculated with whole, formalinized cells from eight passive hemagglutination reference strains of Campylobacter. Fluorescein isothiocyanate-labeled immunoglobulin G from these antisera defined seven new direct fluorescent-antibody serogroups of C. jejuni and one new serogroup of C. coli. This expanded the Campylobacter direct fluorescent antibody system to include 17 serogroups of C. jejuni, 3 serogroups of C. coli, and 2 serogroups of C. fetus. We then compared the passive hemagglutination method (57 serotypes) and the direct fluorescent-antibody method (20 serogroups) for typing strains of C. jejuni and C. coli. The data obtained by testing 101 strains by both methods revealed that the two test systems were measuring completely different sets of antigen complexes. The two serogrouping methods were complementary, and their combined use discriminated among strains more effectively than did either method individually.