Biogeography of the fish pathogen Aeromonas salmonicida inferred by vapA genotyping

Snorre Gulla*, Sion Bayliss, Bryndís Björnsdóttir, Inger Dalsgaard, Olga Haenen, Eva Jansson, Una McCarthy, Felix Scholz, Maaike Vercauteren, David W. Verner-Jeffreys, Timothy Welch, Tom Wiklund, Duncan J. Colquhoun

*Corresponding author for this work

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A recently described typing system based on sequence variation in the virulence array protein (vapA) gene, encoding the A-layer surface protein array, allows unambiguous subtyping of Aeromonas salmonicida. In the present study we compile A-layer typing results from a total of 675 A. salmonicida isolates, recovered over a 59-year period from 50 different fish species in 26 countries. Nine novel A-layer types (15–23) are identified, several of which display a strong predilection towards certain fish hosts, including Cyprinidae- and Pleuronectidae species. Moreover, we find indications that anthropogenic transport of live fish may have aided the near global dissemination of two cyprinid-associated A-layer types. Comparison of whole genome phylogeny and A-layer typing for a subset of strains further resulted in compatible tree topologies, indicating the utility of vapA as a phylogenetic as well as an epizootiological marker in A. salmonicida. A Microreact project ( has been created, allowing public access to the vapA analyses and relevant metadata. In sum, the results generated provide valuable insights into the global population structure of A. salmonicida, particularly in relation to its piscine host spectrum and the geographic distribution of these hosts.
Original languageEnglish
Article numberfnz074
JournalF E M S Microbiology Letters
Issue number7
Number of pages12
Publication statusPublished - 2019


  • Aquaculture
  • Bacterial fish pathogenp
  • Aeromonas salmonicida
  • VapA
  • A-layer
  • Genotyping
  • Host specificity


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