Investigating Antibiotic Susceptibility in Species of Bacteria Isolated from Rainbow Trout (Oncorhynchus Mykiss) with Streptococcosis in Kurdistan Province

Over the last few years, Streptococcus has been one of the serious difficulties in the cold-water fish farms and caused massive economic losses. With respect to outbreak of Streptococcus disease, the survey was carried out in warm seasons using 150 rainbow trout fish with clinical symptoms of streptococcosis. The specimens were randomly collected from Palanghan cold-water fish farm complex located in Kurdistan province. Specimens for bacteria culture were obtained from kidney, liver, and spleen of fish and were cultured on culture media of TSA and BA. Bacterial culture was implemented at the temperature of 220°C for 3-5 days. Species of bacteria were determined following purification using biochemical and molecular tests.
The opacity resulted from the culture of specimens in Muller Hinton Broth's culture medium were compared with McFarland's tube 5% (the number of bacteria 108-109). Then, Muller Hinton Agar's medium was used for performing antibiogram. It was observed that Streptococcus iniae was sensitive to Enrofloxacine, Florfenicole, Doxycycline, Erythromycin, Oxytetracycline, Tetracycline, Lincomycin, Sulfamethoxazole / Trimethoprim, Kanamycin and Neomycin, and resistant to Bacitracin, Lincomycin, Flumequine and Sulfadiazine / Trimethoprim. Streptococcus agalactiae was resistant to Lincomycin and Bacitracin. Moreover, Streptococcus agalactiae was sensitive to Enrofloxacine, Doxycycline, Florfenicole, Lincomycin, Tetracycline, Oxytetracycline, Erythromycin, Kanamycin, Neomycin, Flumequine, Sulfadiazine / Trimethoprim and Sulfamethoxazole / Trimethoprim. Additionally, Lactococccus garvieae was resistant to Bacitracin, Sulfadiazine/Trimethoprim, Lincomycin and Neomycin, and sensitive to Erythromycin, Enrofloxacin, Florfenicole, Doxycycline, Tetracycline, Oxytetracycline, Trimethoprim, Flumequine, Kanamycin, Lincospectin and Sulfamethoxazole/Trimethoprim. The results indicated that the three isolated species of bacteria causing streptococcosis disease, which could create similar clinical signs in trout, were resistant to Bacitracin, Sulfadiazine/Trimethoprim and Lincomycin. In conclusion, in order to avoid growing bacterial resistance and to take the most effective decision in terms of antibiotic therapy, usage of antibiotics without antibiogram must be avoided.