AUTHOR=Girard Sarah B. , Marcoux Pierre-Étienne , Paquet Valérie E. , Zoubaï Sahra , Can Thuy Nhu Vy , Attéré Sabrina A. , Vincent Antony T. , Charette Steve J. 

TITLE=Expansion of the tetracycline resistome in Aeromonas salmonicida with a tet(D) gene found in plasmids pAsa-2900 and pAsa-2900b

JOURNAL=Frontiers in Bacteriology

VOLUME=3

YEAR=2024

URL=https://www.frontiersin.org/journals/bacteriology/articles/10.3389/fbrio.2024.1418706

DOI=10.3389/fbrio.2024.1418706

ISSN=2813-6144

ABSTRACT=<p>Plasmids carrying antibiotic resistance genes occur frequently in <italic>Aeromonas salmonicida</italic> subsp. <italic>salmonicida</italic>, an aquatic pathogen. In this study, we describe three new plasmids found in strains of <italic>A. salmonicida</italic> subsp. <italic>salmonicida</italic> from Québec, Canada: pAsa-2358, pAsa-2900, and pAsa-2900b. The last two plasmids have a <italic>tet</italic>(D) resistance gene against tetracycline, which has not been previously found in <italic>A. salmonicida</italic>. The only difference between these two plasmids is the presence of a florfenicol resistance gene (<italic>floR</italic>) surrounded by two copies of the same insertion sequence, indicating that pAsa-2900 and pAsa-2900b are plasmid variants. All three plasmids represent an issue for aquaculture because they bear resistance genes against antibiotics used to treat infected fish: <italic>floR</italic> and <italic>tet</italic>(A) for pAsa-2358; <italic>floR, sul2</italic>, and <italic>tet</italic>(D) for pAsa-2900; and <italic>sul2</italic> and <italic>tet</italic>(D) for pAsa-2900b. Conjugation assays confirmed that the three plasmids are capable of conjugation with one <italic>A. salmonicida</italic> mesophilic strain, one <italic>A. hydrophila</italic> strain, and <italic>Escherichia coli</italic> DH5<italic>α</italic>; except for pAsa-2358 that is not able to conjugate into <italic>E. coli</italic> DH5α. Based on the results of antibiotic resistance assays, the <italic>tet</italic>(D) gene provides a greater resistance to tetracycline than the <italic>tet</italic>(A) gene found in many <italic>A. salmonicida</italic> subsp. <italic>salmonicida</italic> plasmids. This is the case whether the plasmids are in their parental <italic>A. salmonicida</italic> subsp. <italic>salmonicida</italic> strains or in <italic>Aeromonas</italic> sp. transconjugates. The presence of these three plasmids in <italic>A. salmonicida</italic> subsp. <italic>salmonicida</italic> strengthens the role of this bacterium as a reservoir for antibiotic resistance genes.</p>