Disassociation of Spa type and serovar of an Erysipelothrix rhusiopathiae serovar 6 strain isolated from a diseased pig.

The surface protective antigen (Spa) protein of Erysipelothrix rhusiopathiae is an important component in protecting pigs against swine erysipelas. The Spa protein has been antigenically divided into 3 types: SpaA, SpaB, and SpaC. Swine erysipelas vaccines are formulated with strains of serovar 1 and/or 2, both of which are SpaA-possessing serovars. The association of Spa type with E. rhusiopathiae serovar has been reported, and therefore, the determination of the Spa type and the serovar of clinical isolates are important to assess vaccine efficacy. An E. rhusiopathiae strain, designated Ireland, was isolated from a diseased pig and identified as serovar 6 by a conventional agar gel precipitation test. Sequence analysis of the chromosomal locus presumably defining the serovar antigenicity of E. rhusiopathiae revealed that the gene content and organization of the chromosomal regions of the Ireland strain were identical to those of the serovar 6 reference strain (Tuzok). Sequence analysis of the spa gene and dot blots using a SpaA-specific monoclonal antibody confirmed that, unlike the Tuzok strain possessing SpaB, the Ireland strain expressed SpaA, indicating that the Spa type is not associated with the serovar in this strain. Thus, further investigation into the association between Spa type and serovar of clinical swine isolates is warranted.