Single nucleotide polymorphism genotyping of Erysipelothrix rhusiopathiae isolates from pigs affected with chronic erysipelas in Japan.

Over the past decades, Erysipelothrix rhusiopathiae strains displaying similar phenotypic and genetic profiles of the attenuated, acriflavine-resistant E. rhusiopathiae Koganei 65-0.15 strain (serovar 1a) have been frequently isolated from pigs affected with chronic erysipelas in Japan. In this study, using the conventional PCR assay that was designed to detect strain-specific single nucleotide polymorphism (SNP) sites found in the genome of the vaccine strain, we analyzed E. rhusiopathiae isolates from pigs with chronic disease in farms where the Koganei vaccine was used. Out of a total of 155 isolates, 101 isolates (65.2%) were determined to be the vaccine strain by SNP-based PCR. Among the 101 PCR-positive isolates, four isolates were found to be sensitive to acriflavine.