Received: 16-12-2022 / Accepted: 27-03-2023
The study was conducted to determine the disease characteristics., isolation, identification, and evaluation of antibiotic resistance ofStreptococcus agalactiaecausing blindness in Thai frog(Rana tigerina)raised in Northern provinces ofVietnam. The infected frogs(n=83) were sampled from 26 frog-raising farms in Hanoi, Ha Nam, and Thai Binh provinces. Infected frogsexhibited opaque eyes, blindnessin one or both eyes (78.3%), skin darkening (53.0%), and swelling and hemorrhage liver (69.9%). The bacteria isolated from the eye, brain, kidney and liver of infected frogs were round, convex, cream-coloured, pinpoint (1mm), Gram (+), and of coccus type.Twenty sixstrains isolated from frogs were identified as S. agalactiaebased on morphological, biochemical, and PCR analysis. The LD50of three representative strains were between 1.2×104 to3.5 ×104CFU/frog. The isolated bacteria were highlyresistant to oxytetracycline and sulfamethoxazole/trimethoprim (61.5%), buthighly sensitive to amoxicillin, florfenicol, and erythromycin (65.4-80.8%).These results providesuseful information for effective prevention of the disease caused by S. agalactiaein cultured frogs.