Screening of specific bacteriophages of Lactococcus garvieae strains isolated from rainbow trout lactococcosis outbreaks in Iran

Lactococcosis is a hyperacute systemic disease of fish caused by Lactococcus garvieae which has become one of the devastating problems due to its serious economic damage in aquaculture. The ability of bacteriophages to destroy bacterial cells without harming animal hosts makes them potential anti-bacterial agents for the treatment of bacterial infectious diseases of fish. To isolate the bacterial strains, the suspected fish exhibiting clinical signs of hyperacute hemorrhagic septicemia were collected from several rainbow trout farms. Phenotypic and genotypic features of the isolated bacteria were then studied using microbiological and biochemical tests, 16S rDNA PCR amplification and sequencing. Then, seawater, wastewater and fish farm water and soil samples were used to isolate phages against the fish pathogenic bacteria. After cultivating of the samples, three L. garvieae strains and five L. garvieae phages were isolated and characterized. Although slight differences were observed by transmission electron microscopy, all of the phages were classified as members of the family Podoviridae. These phages have the potential to be used for the prevention and control of lactococcosis in the fish farm.