Determination of antibiotic resistance profiles of Lactococcus garivieae isolated from rainbow trout (Oncorhynchus mykiss) farms in Muğla, Turkey

This study was aimed to determine the current antibiotic resistance of Lactococcus garvieae, which causes significant economic losses in rainbow trout (Oncorhynchus mykiss) farms. For the study, three farms located around a stream were visited in two consecutive disease outbreaks. Bacteria were isolated from the diseased fish and all bacterial isolates were identified using conventional and molecular methods. Then, they were examined for 5 different antibiotic resistance genes and their antibiotic susceptibility profiles were determined using the disc diffusion technique. The results of the study revealed that all 16 isolates had a different antibiotic resistance profile and each should be considered as a separate strain. Additionally, they showed that there may be different L. garvieae strains within and between farms, using the same water source. Comparison of the results with previous studies from the region and different regions of the country revealed that antibiotic resistance is increasing in L. garvieae, and screenings on a limited number of isolates may not give an accurate picture of the final status of antibiotic resistance. These outcomes of the study are discussed in terms of treatment strategies that trout farms in the region should follow when treating lactococcosis.