Identification of Lactococcus spp. strains, isolated from rainbow trout (Oncorhynchus mykiss), by API 20 strep test

Bacterial isolates isolated from rainbow trout samples brought to the Diseases laboratory of our Faculty between 2019-2021 from 6 different rainbow trout farms in the Eastern Black Sea Region were used in this thesis study. Within the scope of this thesis, 25 bacterial isolates isolated from fish samples showing typical disease symptoms sent to the laboratory from trout farms were used. Apart from molecular, histological and serological methods, especially biochemical methods are quite common in the identification of disease agents. Lactococcus garvieae is a species that has been isolated from rainbow trout in recent years and some mistakes have been made in its identification. API 20 Strep identification kit is used for this gram positive bacteria in biochemical identification. In the use of this kit, erroneous results may occur due to problems such as differences in incubation temperature and bacterial growth problems. In this thesis study, it was seen that the majority of isolates tested for API 20 Strep showed 7143111 and 7143511 profiles. It was determined that there was an isolate (D-372) that exactly matched the reference strain. In order to determine the resistance and susceptibility of isolates obtained from rainbow trout to antimicrobial agents, antibiogram test was applied by disc diffusion method. According to the test results, it was observed that all isolates were 100% resistant to Sulfamethoxazole and Streptomycin. It was observed that Amoxicillin was 100%, Doxycycline 76%, Florfenicol 64% effective against Lactococcus spp. isolates.