Coexistence of a novel chromosomal integrative and mobilizable element Tn7548 with two bla-carrying plasmids in a multidrug-resistant Aeromonas hydrophila strain K522 from China.

Objectives: Herein, we detected one multidrug-resistant Aeromonas hydrophila strain K522 co-carrying two bla genes together with a novel chromosomal integrative and mobilizable element (IME) Tn7548 from China. To reveal the genetic characteristics of the novel reservoir of bla and IME in Aeromonas, a detailed genomic characterization of K522 was performed, and a phylogenetic analysis of Tn7412-related IMEs was carried out.

Methods: Carbapenemases were detected by using the immunocolloidal gold technique and antimicrobial susceptibility was tested by using VITEK 2. The whole-genome sequences of K522 were analysed using phylogenetics, detailed dissection, and comparison.

Results: Strain K522 carried a Tn7412-related chromosomal IME Tn7548 and three resistance plasmids pK522-A-KPC, pK522-B-KPC, and pK522-MOX. A phylogenetic tree of 82 Tn7412-related IMEs was constructed, and five families of IMEs were divided. These IMEs shared four key backbone genes: int, repC, and hipAB, and carried various profiles of antimicrobial resistance genes (ARGs). pK522-A-KPC and pK522-B-KPC carried bla and belonged to IncG and unclassified type plasmid, respectively. The bla regions of these two plasmids were the truncated version derived from Tn6296, resulting in the carbapenem resistance of K522.

Conclusion: We first reported A. hydrophila harbouring a novel Tn7412-related IME Tn7548 together with two bla carrying plasmids and a MDR plasmid. Three of these four mobile genetic elements (MGEs) discovered in A. hydrophila K522 were novel. The emergence of novel MGEs carrying ARGs indicated the rapid evolution of the resistance gene vectors in A. hydrophila under selection pressure and would contribute to the further dissemination of various ARGs in Aeromonas.