Abstract
An enzyme-linked immunosorbent assay was used to titrate antisera raised against live cultures of eight type species (biotypes) of Bacteroides with the EDTA-released outer-membrane complex from 29 characterised strains of Bacteroides species. With only minor exceptions, the strains investigated reacted to titre with the antisera raised against the homologous type species and not against the heterologous type species. Cross-reactivity between heterologous species and antiserum was only significant between closely related biotypes. This cross-reactivity could be removed by absorption of the antisera with whole cells. Significant correlation was found between serotype and biotype with this technique.