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Tanaka KH, Vincent AT, Trudel MV, Paquet VE, Frenette M, Charette SJ. (2016) The mosaic architecture of Aeromonas salmonicida subsp. salmonicida pAsa4 plasmid and its consequences on antibiotic resistance. PeerJ Preprints4:e2067v1https://doi.org/10.7287/peerj.preprints.2067v1
Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis in salmonids, is an issue especially because many isolates of this bacterium display antibiotic resistances, which limit treatments against the disease. Recent results suggested the possible existence of alternative forms of pAsa4, a large plasmid found in A. salmonicida subsp. salmonicida and bearing multiple antibiotic resistance genes. The present study reveals the existence of two newly detected pAsa4 variants, pAsa4b and pAsa4c. We present the extensive characterization of the genomic architecture, the mobile genetic elements and the antimicrobial resistances genes of these plasmids in addition to the reference pAsa4 from the strain A449. The analysis showed differences between the three architectures with consequences on the content of resistance genes. The genomic plasticity of the three pAsa4 variants could be partially explained by the action of mobile genetic elements like insertion sequences. Isolates from Canada and Europe that bore similar antibiotic resistance patterns than pAsa4-bearing strains were genotyped and specific pAsa4 variants could be attributed to phenotypic profiles. pAsa4 and pAsa4c were found in Europe, while pAsa4b was found in Canada. The plasticity of pAsa4 variants related to the acquisition of antibiotic resistance indicates that these plasmids may pose a threat in terms of the dissemination of antimicrobial-resistant A.salmonicida subsp. salmonicida bacteria.
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Substitution rate between pAsa4c (JF2267) and pAsa4b (01-B522) using 1-kbp windows
A global alignment of pAsa4b and pAsa4c was performed using stretcher (available as a part of EMBOSS 126.96.36.199) ( Rice et al., 2000 ) , and a custom R script ( R Core Team, 2015 ) was used to visualize the number of substitutions by 1000-bp sliding windows ( Zeileis & Grothendieck, 2005 ) . Transparent lines represent deletions in pAsa4c compared to pAsa4b and should not be considered.
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