Antibiotic susceptibility characteristics of pathogenic bacteria isolated from ornamental fish with dropsy

다국어 초록 (Multilingual Abstract)

Dropsy is a clinical syndrome of diverse origins commonly manifesting as Aeromonas-induced ascites and scale protrusion. This study aimed to identify major dropsy-associated bacterial pathogens in ornamental fish and determine their antibiotic susceptibility. Bacteria were isolated and identified from 13 ornamental fish exhibiting clinical signs of dropsy, including 9 goldfish (Carassius auratus), 2 siamese fighting fish (Betta splendens), and 2 guppies (Poecilia reticulata). Based on 16S rDNA sequence analysis and species-specific PCR, 10 isolates (76.9%) were identified as Aeromonas veronii, one isolate (7.7%) as Aeromonas caviae, one isolate (7.7%) as Citrobacter freundii, and one isolate (7.7%) as Citrobacter braakii. Antimicrobial susceptibility testing showed that all isolates (100%) were resistant to amoxicillin (AML), ampicillin (AMP), lincomycin (MY), and clindamycin (DA). Resistance rates exceeding 90% were also observed for cefadroxil (CFR), oxytetracycline (OT), and oxolinic acid (OA). In contrast, nitrofurantoin (F) exhibited susceptibility rates exceeding 90%. Seven of the eleven Aeromonas isolates were classified as MDR, exhibiting resistance to an average of three acquired antimicrobial classes, and the two Citrobacter isolates were resistant to an average of 5.5 acquired antimicrobial classes. These findings provide fundamental information for the selection of effective therapeutic agents against dropsy-associated bacterial infections in ornamental fish.