in ChileanFarming: Genomic Insights, Phenotypic Traits, Virulence and Field Immune Response.

Abstract

The incidence of furunculosis in juvenile Atlantic salmon,, has increased in recent years in Chile, with isolates ofbeing the primary cause. However, in some cases, molecular diagnostics failed to identify the etiological agent. We previously demonstrated that a proportion of undiagnosed cases was produced by a newstrain. In those cases where the pathogen remained unidentified, we isolated colonies with an-like appearance. Subsequent phylogenetic analysis presented in this work grouped those-like isolates within the Aeromonas piscicola clade. Whole genome sequencing confirmed the taxonomic affiliation, giving additional insights into virulence and antibiotic resistance markers. Indeed, one of the strains showed reduced susceptibility to oxytetracycline. Virulence potential was assessed by in vivo testing in, which resulted in disease with pathognomonic signs of furunculosis. Although the pathogen presents common antigens with, the current vaccine triggered only a modest IgM response againstin the field. Our results support the hypothesis that the increasing incidence of furunculosis in Chile cannot solely be ascribed to the emergence of the new less-virulentstrain, but may partially result from furunculosis-like infections caused bystrains which exhibit a comparable virulence level.