Comprehensive Genomic Analysis of Antimicrobial Resistance in <i>Aeromonas dhakensis</i>

<i>Aeromonas dhakensis</i> is prevalent in aquatic environments in Taiwan and known for its notable antimicrobial resistance. However, comprehensive pan-genomic studies for this species in Taiwan are limited. This study analyzed 28 clinical <i>A. dhakensis</i> isolates using single-molecule real-time sequencing technology, coupled with diverse databases, to elucidate the whole genomes. The focus was on phylogenetic relatedness, antimicrobial resistance genes, and mobile genetic elements. Genomic analysis and multilocus sequence typing were utilized to identify <i>A. dhakensis</i> strains of heterogeneous origins. The detection of various β-lactamase genes (<i>bla</i>_cphA, <i>bla</i>_imiH, <i>bla</i>_AQU, <i>bla</i>_OXA, <i>bla</i>_TEM-1, <i>bla</i>_TRU-1, and <i>bla</i>_VEB) in clinical <i>A. dhakensis</i> isolates raises concern, especially considering the use of carbapenems and third-generation cephalosporins in patients with severe infections. Notably, most <i>A. dhakensis</i> strains carry chromosome-encoded β-lactamases, including AmpC, metallo-β-lactamase, and oxacillinase, and were susceptible to cefepime in drug susceptibility tests. <i>A. dhakensis</i> strains were also susceptible to aminoglycosides, fluoroquinolones, tigecycline, and trimethoprim/sulfamethoxazole. Three of the 28 <i>A. dhakensis</i> isolates carried plasmids containing an array of drug resistance genes, suggesting this species is likely a recipient or donor of drug resistance genes through horizontal gene transfer. Our findings provide valuable insights into the antimicrobial resistance of <i>A. dhakensis</i>, highlighting the medical implications of its β-lactamase diversity and its potential role in the horizontal gene transfer of drug resistance genes.