Classification of a HypervirulentAeromonas hydrophilaPathotype Responsible for Epidemic Outbreaks in Warm-Water Fishes.
Lineages of hypervirulentAeromonas hydrophila(vAh) are the cause of persistent outbreaks of motileAeromonassepticemia in warm-water fishes worldwide. Over the last decade, this virulent lineage ofA. hydrophilahas resulted in annual losses of millions of tons of farmed carp and catfish in the People's Republic of China and the United States (US). Multiple lines of evidence indicate US catfish and Asian carp isolates ofA. hydrophilaaffiliated with sequence type 251 (ST251) share a recent common ancestor. To address the genomic context for the putative intercontinental transfer and subsequent geographic spread of this pathogen, we conducted a core genome phylogenetic analysis on 61Aeromonasspp. genomes, of which 40 were affiliated withA. hydrophila, with 26 identified as epidemic strains. Phylogenetic analyses indicate all ST251 strains form a coherent lineage affiliated withA. hydrophila. Within this lineage, conserved genetic loci unique toA. hydrophilawere identified, with some genes present in consistently higher copy numbers than in non-epidemicA. hydrophilaisolates. In addition, results from analyses of representative ST251 isolates support the conclusion that multiple lineages are present within US vAh isolated from Mississippi, whereas vAh isolated from Alabama appear clonal. This is the first report of genomic heterogeneity within US vAh isolates, with some Mississippi isolates showing closer affiliation with the Asian grass carp isolate ZC1 than other vAh isolated in the US. To evaluate the biological significance of the identified heterogeneity, comparative disease challenges were conducted with representatives of different vAh genotypes. These studies revealed that isolate ZC1 yielded significantly lower mortality in channel catfish, relative to Alabama and Mississippi vAh isolates. Like other Asian vAh isolates, the ZC1 lineage contains all core genes for a complete type VI secretion system (T6SS). In contrast, more virulent US isolates retain only remnants of the T6SS (clpB, hcp, vgrG, andvasH) which may have functional implications. Collectively, these results characterize a hypervirulentA. hydrophilapathotype that affects farmed fish on multiple continents.
Department of Biological Sciences, Auburn University Auburn, AL, USA.
Cody R
CR
Rasmussen-Ivey
Department of Biological Sciences, Auburn University Auburn, AL, USA.
Mohammad J
MJ
Hossain
Department of Biological Sciences, Auburn University Auburn, AL, USA.
Sara E
SE
Odom
School of Fisheries, Aquaculture and Aquatic Sciences Auburn, AL, USA.
Jeffery S
JS
Terhune
Alabama Fish Farming Center Greensboro, AL, USA.
William G
WG
Hemstreet
Aquatic Animal Health Research Unit, United States Department of Agriculture-Agricultural Research Service Auburn, AL, USA.
Craig A
CA
Shoemaker
Aquatic Animal Health Research Unit, United States Department of Agriculture-Agricultural Research Service Auburn, AL, USA.
Dunhua
D
Zhang
Aquatic Animal Health Research Unit, United States Department of Agriculture-Agricultural Research Service Auburn, AL, USA.
De-Hai
DH
Xu
Thad Cochran National Warmwater Aquaculture Center, College of Veterinary Medicine, Mississippi State University Stoneville, MS, USA.
Matt J
MJ
Griffin
College of Veterinary Medicine, Nanjing Agricultural University Nanjing, China.
Yong-Jie
YJ
Liu
Departamento de Ciencias Médicas Básicas, Facultad de Medicina y Ciencias de la Salud, IISPV, Universidad Rovira i Virgili Reus, Spain.
Maria J
MJ
Figueras
Department of Biological Sciences, Auburn University Auburn, AL, USA.
Scott R
SR
Santos
Department of Pathobiology, Auburn University Auburn, AL, USA.
Joseph C
JC
Newton
Department of Biological Sciences, Auburn University Auburn, AL, USA.
Mark R
MR
Liles
Aeromonas hydrophila; bacteria; carp; catfish; comparative genomics; emerging disease; pathogenesis