Detection of Variants of the pRAS3, pAB5S9, and pSN254 Plasmids in Aeromonas salmonicidasubsp. salmonicida: Multidrug Resistance, Interspecies Exchanges, and Plasmid Reshaping

ABSTRACTThe ubiquitous water-borne Gram-negative bacterium Aeromonas salmonicidasubsp. salmonicidais the causative agent of furunculosis, a worldwide disease in fish farms. Plasmids carrying antibiotic resistance genes have already been described for this bacterium. The aim of the present study was to identify and characterize additional multidrug resistance plasmids in A. salmonicidasubsp. salmonicida. We sequenced the plasmids present in two multiple antibiotic-resistant isolates using high-throughput technologies. We also investigated 19 other isolates with various multidrug resistance profiles by genotyping PCR and assessed their resistance to tetracycline. We identified variants of the pAB5S9 and pSN254 plasmids that carry several antibiotic resistance genes and that have been previously reported in bacteria other than A. salmonicidasubsp. salmonicida, which suggests a high level of interspecies exchange. Genotyping analyses and the antibiotic resistance profiles of the 19 other isolates support the idea that multiple versions of pAB5S9 and pSN254 exist in A. salmonicidasubsp. salmonicida. We also identified variants of the pRAS3 plasmid. The present study revealed that A. salmonicidasubsp. salmonicidaharbors a wide variety of plasmids, which suggests that this ubiquitous bacterium may contribute to the spread of antibiotic resistance genes in the environment.