ARS | Publication request: Comparative genomics of Aeromonas hydrophila isolates from an epidemic in channel catfish

Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 20, 2011
Publication Date: May 21, 2011
Citation: Liles, M., Hemstreet, W., Waldbieser, G., Griffin, M., Khoo, L., Bebak, J.A., Garcia, J.C., Goodwin, A., Capps, N., Hayden, K., Terhune, J. 2011. Comparative genomics of Aeromonas hydrophila isolates from an epidemic in channel catfish [abstract]. American Society for Microbiology. Poster No. 1489.

Technical Abstract: Background Aeromonas hydrophila was identified as the etiologic agent infecting farmed channel catfish in 2009/2010, resulting in higher mortality rates than typical for motile Aeromonas septicemia with over 5 million pounds of catfish lost to this outbreak. The biochemistry, molecular phylogeny, and genome sequences of recent A. hydrophila isolates were investigated. Methods A. hydrophila isolates were cultured on blood agar and pure cultures were subjected to biochemical tests and DNA extracted for PCR of 16S rRNA or gyrB genes. A maximum parsimony analysis of A. hydrophila sequences indicated representative strains to select for genome sequencing. Twelve A. hydrophila strains were sequenced at >50-fold coverage by bar-coded Illumina sequencing and genome comparisions were conducted using the CLC Genomics Workbench. Results Biochemical tests were similar to other A. hydrophila strains. Recent isolates had 100% identity to 16SrRNA genes and > 99% identity to gyrB genes from other A. hydrophila strains, with gyrB allowing better resolution and grouping all but one isolate (ML09-123) as a coherent clade. Genome sequencing supports the close genome similarity of recent virulent strains, with the exception of strain ML09-123. Gene sequences were identified that were unique to recent virulent strains (e.g. prophage, inositol catabolism) and were used to generate 26 virulent strain-specific primer sets that are being tested against strain collections from AL, MS, and AR. Conclusion A. hydrophila strains from a recent epidemic in channel catfish are highly similar in phenotype and genotype. Ongoing studies will facilitate molecular diagnostics, determination of virulence factors, and treatment regimes for these A. hydrophila pathogenic strains.