Antimicrobial Resistance, Virulence and Resistance Genes in Aeromonas 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 blaTEM, 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.