RT Journal Article SR Electronic(1) A1 Vincent, Antony T. A1 Emond-Rheault, Jean-Guillaume A1 Barbeau, Xavier A1 Attéré, Sabrina A. A1 Frenette, Michel A1 Lagüe, Patrick A1 Charette, Steve J.YR 2016 T1 Antibiotic resistance due to an unusual ColE1-type replicon plasmid in Aeromonas salmonicida JF Microbiology, VO 162 IS 6 SP 942 OP 953 DO https://doi.org/10.1099/mic.0.000286 PB Microbiology Society, SN 1465-2080, AB Aeromonas salmonicida subsp. salmonicida is a fish pathogen known to have a rich plasmidome. In the present study, we discovered an isolate of this bacterium bearing an additional unidentified small plasmid. After having sequenced the DNA of that isolate by next-generation sequencing, it appeared that the new small plasmid is a ColE1-type replicon plasmid, named here pAsa7. This plasmid bears a functional chloramphenicol-acetyltransferase-encoding gene (cat-pAsa7) previously unknown in A. salmonicida and responsible for resistance to chloramphenicol. A comparison of pAsa7 with pAsa2, the only known ColE1-type replicon plasmid usually found in A. salmonicida subsp. salmonicida, revealed that even if both plasmids share a high structural similarity, it is still unclear if pAsa7 is a derivative of pAsa2 since they showed several mutations at the nucleotide level. Transcriptomic analysis revealed that the cat-pAsa4 gene, another chloramphenicol-acetyltransferase-encoding gene, found on the large plasmid pAsa4, was significantly more transcribed than cat-pAsa7. This was correlated with a higher chloramphenicol resistance for isolates bearing pAsa4 compared with the one having pAsa7. Finally, a phylogenetic analysis showed that both CAT-pAsa4 and CAT-pAsa7 proteins were in different clusters. The clustering was supported by the identity of residues involved in the catalytic site. In addition, to give a better understanding of the large drug-resistance panel of A. salmonicida, this study reinforces the hypothesis that A. salmonicida subsp. salmonicida is a considerable reservoir for mobile genetic elements such as plasmids., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.000286