Cross-reactivity of Bacteroides fragilis O antigens.

The cross-reactivity of O antigens prepared from Bacteroides fragilis, other Bacteroides species and from Fusobacterium has been examined by indirect haemagglutination and inhibition of haemagglutination. Fifteen of 20 B. fragilis ss. fragilis strains showed O-antigenic cross-reactivity with one or more of the test strains of B. fragilis ss. fragilis: NCTC 9343, Lille E 323 and SBL B55. The same applies also to 3 strains classified as B. coagulans, B. hypermegas and B. putredinis. The multispecificity of B. fragilis O antigens is pronounced. Test systems for demonstration of 9 specificities, all harboured by one or more of the 3 test strains, have been worked out.