Furunculosis caused by Aeromonas piscicola: genomic insights, phenotypic traits and field immune response
The incidence of furunculosis in juvenile Atlantic salmon, Salmo salar, has increased in recent years in Chile being isolates of Aeromonas salmonicida the primary cause. However, in some cases, molecular diagnostic failed to identify the etiological agent. In a previous work, we demonstrated that a proportion of undiagnosed cases were produced by a new A. salmonicida strain. In those which the pathogen remained unidentified, we isolated colonies with an A. salmonicida-like appearance. In this work, phylogenetic analysis grouped those A. salmonicida-like isolates within the Aeromonas piscicola clade. Whole genome sequencing confirmed the taxonomic affiliation, giving additional insights into virulence and antibiotic resistance markers. Interestingly, the isolates shown to be mesophilic resulting susceptible to all antibiotics tested. Furthermore, virulence potential was assessed by in vivo testing on S. salar, demonstrating a disease with furunculosis pathognomonic signs. Although the pathogen presented common antigens with A. salmonicida, the current vaccine is able to trigger only a modest IgM response against A. piscicola in the field. Likely, current furunculosis incidence in Chile cannot be ascribed to the emergence of the new A. salmonicida strain, but also may result from infections caused by an A. piscicola strain which exhibits a comparable virulence level.