Polyphasic characterization of Aeromonas salmonicida isolates recovered from salmonid and non‐salmonid fish

Abstract

Michigan's fisheries rely primarily upon the hatchery propagation of salmonid fish for release in public waters. One limitation on the success of these efforts is the presence of bacterial pathogens, including Aeromonas salmonicida, the causative agent of furunculosis. This study was undertaken to determine the prevalence of A. salmonicida in Michigan fish, as well as to determine whether biochemical or gene sequence variability exists among Michigan isolates. A total of 2202 wild, feral and hatchery-propagated fish from Michigan were examined for the presence of A. salmonicida. The examined fish included Chinook salmon, Oncorhynchus tshawytscha (Walbaum), coho salmon, O. kisutcha (Walbaum), steelhead trout, O. mykiss (Walbaum), Atlantic salmon, Salmo salar L., brook trout, Salvelinus fontinalis (Mitchill), and yellow perch, Perca flavescens (Mitchill). Among these, 234 fish yielded a brown pigment-producing bacterium that was presumptively identified as A. salmonicida. Further phenotypic and phylogenetic analyses identified representative isolates as Aeromonas salmonicida subsp. salmonicida and revealed some genetic and biochemical variability. Logistic regression analyses showed that infection prevalence varied according to fish species/strain, year and gender, whereby Chinook salmon and females had the highest infection prevalence. Moreover, this pathogen was found in six fish species from eight sites, demonstrating its widespread nature within Michigan.

INFECTION OF SEA LAMPREY WITH AN UNUSUAL STRAIN OFAEROMONAS SALMONICIDA

“…Recovered bacterial isolates were presumptively assigned to the genus Aeromonas, and then identified to species and subspecies according to Holt et al (2000) and Cipriano and Bullock (2001) and as described by Diamanka et al (2013). Biochemical test results that differed from the A. salmonicida subsp.…”

“…Antibiotic susceptibility testing was performed using the Kirby-Bauer disc diffusion method (Bauer et al 1966), using ampicillin, oxytetracycline, sulfamethoxazole-trimethoprim, novobiocin, erythromycin, and O/129 (2,4-diamino-6,7-diisopropylpteridine) and as described in Diamanka et al (2013).…”

“…Bacterial processing, DNA extraction and quantification, and PCR analysis using the Miyata primers (Miyata et al 1996), which are specific for A. salmonicida subsp. salmonicida (Byers et al 2002), conducted as described (Diamanka et al 2013) with the exception that a MastercyclerH Pro Thermalcycler (Eppendorf, Hauppauge, New York, USA) was used. The generation of a 512-base pair (bp) amplicon was considered as positive identification for A. salmonicida subsp.…”

“…Amplicons from the 16S rRNA and gyrB genes were sequenced as previously described (Diamanka et al 2013). Contigs were assembled in the BioEdit Sequence Alignment Editor (Hall 1999) using the contig assembly program (CAP).…”

“…salmonicida type strain sequenced in our laboratory, as well as with the homologous sequences from the whole genome and others subspecies found within the BLAST database. Nucleotide sequences of the 16S rRNA and gyrB genes were aligned independently, and neighbor-joining analysis and phylogenetic trees were constructed as described (Diamanka et al 2013). …”