Abstract
The cross-reactivity of O antigens prepared from B. fragilis, other Bacteroides spp. and Fusobacterium was examined by indirect hemagglutination and hemagglutination inhibition tests. Fifteen of the 20 B. fragilis ssp. fragilis strains showed O antigenic cross-reactivity with .gtoreq. of the test strains of B. fragilis ssp. fragilis NCTC 9343, Lille E 323 and SBL B55. The same also applied to 3 strains classified as B. coagulans, B. hypermegas and B. putredinis. The multispecificity of B. fragilis O antigens is pronounced. Test systems for 9 specificities, all harbored by .gtoreq. of the 3 test strains, were demonstrated.