Antibiotic resistance due to an unusual ColE1-type replicon plasmid in Aeromonas salmonicida

Abstract

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 nextgeneration 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 catpAsa4 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.

Plasmid composition in Aeromonas salmonicida subsp. salmonicida 01-B526 unravels unsuspected type three secretion system loss patterns

“…salmonicida is also known for its genomic variability. Different kinds of recombination have formed plasmid and genomic island variants with altered gene contents that result in phenotypic changes [5, 6, 15–19]. This bacterium, beyond mediating gene transfer, could thus provide a new combination of those genes.…”

The mosaic architecture ofAeromonas salmonicidasubsp.salmonicidapAsa4 plasmid and its consequences on antibiotic resistance

“…For example, more and more antibiotic-resistant A. salmonicida subsp. salmonicida strains are being isolated and characterized, many of them bearing resistance genes on plasmids (McIntosh et al, 2008; Piotrowska & Popowska, 2015; Sorum et al, 2003; Vincent et al, 2016a; Vincent et al, 2014b). …”

Beyond the A‐layer: adsorption of lipopolysaccharides and characterization of bacteriophage‐insensitive mutants of Aeromonas salmonicida subsp. salmonicida

“…The plasmid pAsa7 (Vincent et al , ) is a small ColE1‐type replicon plasmid (~5 270 bp) that bears a functional resistance to chloramphenicol and is naturally found in A. salmonicida subsp. salmonicida.…”