Molcular characterization of Lactococcus garvieae isolates recovered from rainbow trout

This study aims to characterize Lactococcus garvieae strains isolated from six rainbow trout (Oncorhynchus mykiss) farms in Van province, Turkey, using microbiological and molecular techniques. The selected farms are significant for regional aquaculture, conducting annual production cycles from larvae to market-size fish and serving as broodstock sources. From each farm, six symptomatic fish were sampled. Kidney tissues were cultured on TSA medium, and the resulting colonies were subjected to Gram staining, catalase, oxidase, and motility tests. Colonies showing similar characteristics to L. garvieae underwent DNA extraction and Real-Time PCR targeting the 16S rRNA gene. Positive isolates were further examined for antibiotic resistance genes (TetA, FloR) and virulence genes (Hemolysin, Adhesive Pav). The results indicated substantial genetic variability among farms, with widespread detection of resistance genes, highlighting the selective pressure from antibiotic usage. Based on these findings, recommendations included implementing filtration systems tailored to each facility and promoting anonymous sharing of bacterial disease profiles to improve regional fish health management.