Molecular and Phenotypic Characterization of MDR and XDR Aeromonas spp. Isolated from Hospital Wastewater

Hospital wastewater (HWW) is increasingly recognized as an environmental hotspot for the selection and dissemination of antimicrobial resistance (AMR). Although surveillance programs primarily target ESKAPE pathogens, the contribution of environmental bacteria such as Aeromonas spp. remains poorly characterized. The aim of this work was to investigate antimicrobial resistance mechanisms, focusing on carbapenem and cephalosporin resistance, in Aeromonas spp. recovered from HWW. Thirty Aeromonas isolates were identified by rpoD restriction fragment length polymorphism analysis and characterized by antimicrobial susceptibility testing, detection of β-lactam resistance genes, class 1 integrons, and genetic relatedness using ERIC-PCR fingerprinting. All isolates exhibited operationally defined multidrug-resistant (MDR) or extensively drug-resistant (XDR) phenotypes, with resistance predominating against cephalosporins, carbapenems, and trimethoprim–sulfamethoxazole. The clinically relevant gene families/groups blaKPC family, blaOXA-48-like, blaCTX-M group 1, and blaSHV were detected by PCR, whereas blaNDM, blaVIM, blaIMP, and mcr-1 were absent. Class 1 integrons were identified in 36.7% of isolates, revealing diverse cassette arrays carrying dfrA and aadA resistance genes. ERIC-PCR demonstrated high fingerprint diversity with limited genetic relatedness. Microbiological surveillance of HWW revealed that Aeromonas populations constitute an environmental reservoir of clinically relevant β-lactam resistance determinants, supporting further evaluation of their potential role in AMR surveillance strategies at the hospital–environment interface.