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 alleles ( .43 and .2) with two carbapenemase genes ( and ) were encoded in a single strain isolated from hospital sewage. Our phylogenetic analysis revealed that the gene clustered with (with 95.55% amino acid identity), while the gene clustered with (with 68.68% amino acid identity). BLAST search against GenBank showed that was exclusively detected in spp. Mobile genetic elements were not found in the genetic context of , suggesting that the dissemination of in spp. may be dependent on vertical transfer or recombination. The was adjacent to a recombinase gene and flanked by two IS elements, indicating a potential mobilization mechanism mediated by recombination and/or ISs. The gene was located on an IncU plasmid and adjacent to an IS . In summary, our study provides evidence for spp. as one of the potential reservoirs of colistin and carbapenem resistance genes.IMPORTANCEThe study discovered two novel genes ( and ) and two carbapenemase genes ( and ) in a single 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 is only present in 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 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.