A Study on Detecting Infections Caused by Some Coccal Species on the Cultured Rainbow Trout (Oncorhynchus mykiss, W.)

The aim of this study was to investigate whether Lactococcus garvieae, Streptococcus agalactiae (synonym S. difficilis) and Streptococcus iniae were causative agents of disease outbreaks observed in different rainbow trout fish farms in the Mediterranean region of Turkey. The field studies were started in April of 2012 and completed in September. Phenotypic tests, the API 20 strep and PCR technique were used to identify the isolated 55 strains. Darkening of the skin colour, clouding of cornea, exophthalmus, intraocular hemorrhagy, pale gills and haemorrhages at the base of fins were observed in the diseased fish samples. Histopathologically, necrosis on the kidney glomeruli and tubules, change of gill structure due to hyperplasia and fusion, presence of heavy depositions in the MMCs in the kidney, necrotic degenerations in the hepatocytes, depletions of splenecytes and mucosa epithelium of the stomach were determined. According to the results of the study, Lactococcus garvieae was isolated from sick fish while Streptococcus agalactiae and S. iniae were not isolated. With this result, it was understood that L. garvieae was the main responsible agent for disease outbreaks in the trout farms that were sampled in the region. In the study, it was found that the isolates were resistant to at least two antimicrobial agents. This state can be explained by the increased resistance of bacteria against antimicrobial agents used in the farm conditions. The results of antibiogram susceptibility testing suggest that current vaccine development studies against disease should be increased because the development of resistance of bacteria increases, preoccupying that this resistance development may also be transmitted to other bacterial species in the environment