Antimicrobial Resistance, Virulence and Resistance Genes in <i>Aeromonas</i> From Diseased Fish in China's Major Freshwater Aquaculture Regions

This study aimed to characterise Aeromonas isolates from diseased freshwater fish in Jiangxi Province, with a focus on their species distribution, genetic diversity, virulence and resistance gene profiles and antibiotic susceptibility. A total of 105 Aeromonas strains were isolated and identified, with Aeromonas veronii being the dominant species (68.6%). ERIC-PCR divided the isolates into 76 molecular types. Most isolates carried multiple virulence genes. These isolates exhibited high resistance to ampicillin (98.1%), erythromycin (84.7%) and rifampicin (54.3%), but were susceptible to chloramphenicol, florfenicol and ceftriaxone. The overall multidrug-resistance (MDR) rate was 64.8%. Aeromonas hydrophila showed a significantly higher MDR rate (95%) than both A. veronii and Aeromonas jandaei (each 58.3%). Resistance genes such as bla_TEM, qnrA and qnrS were prevalent, while others, including tetA and sul1, were less common. Two class 1 integron gene cassettes were identified: 'drfB4-catB3' (n = 16) and 'drfA17-aadA5' (n = 1). Aeromonas isolates in Jiangxi exhibit high genetic diversity, significant virulence potential, andconcerning antibiotic resistance profiles. Of particular concern is A. hydrophila, which poses a high multidrug-resistance risk.