First report of multidrug-resistant carbapenemase-producing Aeromonas caviae co-harboring mcr-3.43 and mcr-7.2 .

Hospital sewage serves as a crucial reservoir for antibiotic resistance genes. As colistin and carbapenems are the last-resort antibiotics, the emergence of their resistance genes has become a significant concern in clinical settings. In this study, we found that two novel mcr alleles ( mcr-3 .43 and mcr-7 .2) with two carbapenemase genes ( bla NDM-1 and bla KPC-2 ) were encoded in a single Aeromonas caviae strain isolated from hospital sewage. Our phylogenetic analysis revealed that the mcr-3.43 gene clustered with mcr-3.17 (with 95.55% amino acid identity), while the mcr-7.2 gene clustered with mcr-7.1 (with 68.68% amino acid identity). BLAST search against GenBank showed that mcr-7.2 was exclusively detected in Aeromonas spp. Mobile genetic elements were not found in the genetic context of mcr-7.2 , suggesting that the dissemination of mcr-7.2 in Aeromonas spp. may be dependent on vertical transfer or recombination. The bla NDM-1 was adjacent to a recombinase gene and flanked by two IS 91 elements, indicating a potential mobilization mechanism mediated by recombination and/or ISs. The bla KPC-2 gene was located on an IncU plasmid and adjacent to an IS Kpn6 . In summary, our study provides evidence for Aeromonas spp. as one of the potential reservoirs of colistin and carbapenem resistance genes.IMPORTANCEThe study discovered two novel mcr genes ( mcr-3.43 and mcr-7.2 ) and two carbapenemase genes ( bla NDM-1 and bla KPC-2 ) in a single Aeromonas caviae strain retrieved from hospital sewage. Using phylogenetic analysis and comparative data evaluation, the study revealed the genetic relatedness and dissemination potential of the detected resistance genes. With the exclusive discovery that mcr-7.2 is only present in Aeromonas spp. and the lack of mobile genetic elements in its genetic context, there is a strong indication of limited dissemination. The identification of these four resistance genes in a single strain of Aeromonas provided valuable insights into their potential presence in this genus. This study revealed that hospital sewage functions as a significant reservoir for antibiotic resistance genes, including colistin and carbapenem resistance genes.