pirABvp-Bearing Vibrio parahaemolyticus and Vibrio campbellii Pathogens Isolated from the Same AHPND-Affected Pond Possess Highly Similar Pathogenic Plasmids

Abstract

Acute hepatopancreatic necrosis disease (AHPND) is a severe shrimp disease originally shown to be caused by virulent strains of Vibrio parahaemolyticus (VP AHPND ). Rare cases of AHPND caused by Vibrio species other than V. parahaemolyticus were reported. We compared an AHPND-causing V. campbellii (VC AHPND ) and a VP AHPND isolate from the same AHPND-affected pond. Both strains are positive for the virulence genes pirAB vp . Immersion challenge test with Litopenaeus vannamei indicated the two strains possessed similar pathogenicity. Complete genome comparison showed that the pirAB vp -bearing plasmids in the two strains were highly homologous, and they both shared high homologies with plasmid pVA1, the reported pirAB vp -bearing plasmid. Conjugation and DNA-uptake genes were found on the pVA1-type plasmids and the host chromosomes, respectively, which may facilitate the dissemination of pirAB vp . Novel variations likely driven by ISVal1 in the genetic contexts of the pirAB vp genes were found in the two strains. Moreover, the VC AHPND isolate additionally contains multiple antibiotic resistance genes, which may bring difficulties to control its future outbreak. The dissemination of the pirAB vp in non-parahaemolyticus Vibrio also rises the concern of missing detection in industrial settings since the isolation method currently used mainly targeting V. parahaemolyticus. This study provides timely information for better understanding of the causes of AHPND and molecular epidemiology of pirAB vp and also appeals for precautions to encounter the dissemination of the hazardous genes.