spaB-positive Erysipelothrix rhusiopathiae, a novel teleost pathogen isolated from cultured barramundi

Abstract

Members of the genus Erysipelothrix are emergent pathogens of cultured eels, as well as several characid and cyprinid species. Since 2013, E. rhusiopathiae has been reported from diseased barramundi ( Lates calcarifer) cultured in North America; we recovered 8 E. rhusiopathiae isolates from diseased fish during different outbreaks from the same farm. The E. rhusiopathiae isolates from barramundi were compared phenotypically and genetically to E. piscisicarius isolates characterized from ornamental fish and E. rhusiopathiae recovered from aquatic and terrestrial animals. All barramundi isolates were PCR-positive for the surface protective antigen type B ( spaB) gene, and shared ≥ 99.7% sequence similarity among concatenated multilocus sequence analysis gene sequences, indicating a high degree of genetic homogeneity. These isolates were > 99% similar to other spaB-positive isolates from marine invertebrates and marine mammals, consistent with findings for other spa types. The spaA and spaB isolates shared < 98% similarity, as well as < 90% similarity with spaC-positive E. piscisicarius. Similar clonality among the spaB isolates was observed using repetitive element palindromic PCR. In experimental intracoelomic injection challenges conducted to fulfill Koch postulates, 67% of exposed tiger barbs ( Puntigrus tetrazona) died within 14 d of challenge. Our study supports previous work citing the genetic variability of Erysipelothrix spp. spa types and the emergence of members of the genus Erysipelothrix as nascent fish pathogens.