Phenotypic and MALDI-TOF MS Characterization of Presumptive Antimicrobial-Resistant Bacteria from Hungarian Aquatic Environments

Antimicrobial resistance (AMR) in aquaculture environments has become an increasing concern due to the dissemination of antibiotic-resistant bacteria in aquatic ecosystems. This study investigated the occurrence of presumptive antimicrobial-resistant bacteria in commercial fish farms in Hajdú-Bihar county, Hungary. Between 2023 and 2024, water samples were collected from fishponds from Hajdúszoboszló, Biharugra, and Debrecen, followed by membrane filtration with 0.45 µm pore size mixed cellulose ester membrane filters, bacterial isolation using selective media including vancomycin-resistant enterococci (VRE) agar, Eosin Methylene Blue (EMB) agar, and Endo’s medium. The phenotypic characterization revealed the presence of diverse bacterial populations that could be associated with potential antimicrobial resistance. Bacterial identification using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) showed several bacterial genera, predominantly Acinetobacter, Pseudomonas, Enterococcus, Bacillus, and Escherichia. A total of 16 presumptive antimicrobial-resistant bacterial isolates recovered from selective media were identified using MALDI-TOF MS. Several detected species, including Acinetobacter baumannii, Pseudomonas aeruginosa, Enterococcus faecium, and Enterococcus faecalis, are recognized as opportunistic bacteria associated with antimicrobial resistance dissemination. The findings demonstrate that aquaculture waters in Hajdú-Bihar county may serve as reservoirs of antimicrobial-resistant bacteria.