title: An Asian origin of virulent Aeromonas hydrophila responsible for disease epidemics in United States-farmed catfish.
abstract: Since 2009, catfish farming in the southeastern United States has been severely impacted by a highly virulent and clonal population of Aeromonas hydrophila causing motile Aeromonas septicemia (MAS) in catfish. The possible origin of this newly emerged highly virulent A. hydrophila strain is unknown. In this study, we show using whole-genome sequencing and comparative genomics that A. hydrophila isolates from diseased grass carp in China and catfish in the United States have highly similar genomes. Our phylogenomic analyses suggest that U.S. catfish isolates emerged from A. hydrophila populations of Asian origin. Furthermore, we identified an A. hydrophila strain isolated in 2004 from a diseased catfish in Mississippi, prior to the onset of the major epidemic outbreaks in Alabama starting in 2009, with genomic characteristics that are intermediate between those of the Asian and Alabama fish isolates. Investigation of A. hydrophila strain virulence demonstrated that the isolate from the U.S. catfish epidemic is significantly more virulent to both channel catfish and grass carp than is the Chinese carp isolate. This study implicates the importation of fish or fishery products into the United States as the source of highly virulent A. hydrophila that has caused severe epidemic outbreaks in United States-farmed catfish and further demonstrates the potential for invasive animal species to disseminate bacterial pathogens worldwide.
  
  
  OBJECTIVE
  Catfish aquaculture farming in the southeastern United States has been severely affected by the emergence of virulent Aeromonas hydrophila responsible for epidemic disease outbreaks, resulting in the death of over 10 million pounds of catfish. Because the origin of this newly emerged A. hydrophila strain is unknown, this study used a comparative genomics approach to conduct a phylogenomic analysis of A. hydrophila isolates obtained from the United States and Asia. Our results suggest that the virulent isolates from United States-farmed catfish have a recent common ancestor with A. hydrophila isolates from diseased Asian carp. We have also observed that an Asian carp isolate, like recent U.S. catfish isolates, is virulent in catfish. The results from this study suggest that the highly virulent U.S. epidemic isolates emerged from an Asian source and provide another example of the threat that invasive species pose in the dissemination of bacterial pathogens.
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, Alabama, USA.
authors.forename: Mohammad J
authors.initials: MJ
authors.lastname: Hossain
authors.affiliation: School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, Alabama, USA.
authors.forename: Dawei
authors.initials: D
authors.lastname: Sun
authors.affiliation: Department of Biology and Physics, Kennesaw State University, Kennesaw, Georgia, USA.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: McGarey
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, Alabama, USA.
authors.forename: Shannon
authors.initials: S
authors.lastname: Wrenn
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, Alabama, USA.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Alexander
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padua, Legnaro, Italy.
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Martino
authors.affiliation: Pearl River Fisheries Research Institute, Guangzhou, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Xing
authors.affiliation: School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, Alabama, USA.
authors.forename: Jeffery S
authors.initials: JS
authors.lastname: Terhune
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, Alabama, USA lilesma@auburn.edu.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Liles
mesh_terms: D016980:Aeromonas hydrophila / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D000383:Agriculture; D000818:Animals; D002397:Catfishes / Q000821:virology*; D030541:Databases, Genetic; D005393:Fish Diseases / Q000453:epidemiology*; D016905:Gram-Negative Bacterial Infections / Q000662:veterinary*; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D014481:United States / Q000453:epidemiology