Proposed revisions to the serological typing system for Treponema hyodysenteriae.

Antisera were prepared in rabbits against seven well-characterized strains of Treponema hyodysenteriae of known serotype, and reacted in agarose gel double immunodiffusion tests (AGDP) with lipopolysaccharide (LPS) extracted from 18 Western Australian isolates of the organism. Eight isolates were provisionally typed by this method, but sera raised against one 'typed' and two 'untypable' local isolates reacted in an unexpected fashion with LPS from other local and type strains. Serum raised against the 'typed' local isolate reached with LPS from other previously untyped local isolates: this indicated the presence of more than one major LPS antigen amongst certain local isolates, and was confirmed by cross-absorption of sera. Sera raised against apparently untypable local isolates reacted with LPS from certain type organisms, thus suggesting the presence of complex antigenic relationships between LPS antigens. The serotyping system for T. hyodysenteriae which was proposed by Baum & Joens (1979) uses unabsorbed antisera and is made unworkable by these observations. Instead we propose placing organisms which share common LPS antigens into serogroups A to E, members of which are defined by their reactivity with unabsorbed sera raised against a type organism for the group. We suggest strains B78, WA1, B169, A1 and WA6 respectively as being the most suitable type organisms for the five serogroups identified so far. Isolates possessing additional unique LPS antigens can be regarded as serotypes within the serogroup. However the serotype of an isolate can only be established if antiserum is prepared against it, and this serum continues to react homologously after cross-absorption with bacteria from other serotypes within the serogroup.