• Journal of Microbiology and Biotechnology
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• v.22 no.4
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• pp.526-529
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• 2012

The present study was aimed to investigate the effect of a probiotic, Enterococcus faecium, on the immune responses against infection with the marine fish pathogen Lactococcus garvieae in olive flounder (Paralichthys olivaceus). The immune responses were assessed by lysozyme activity, complement activity, protease activity, and expression of proinflammatory cytokines by RT-PCR. The lysozyme and complement activities were increased between 9 to 15 and 9 to 13 days, respectively, and antiprotease activity was slightly elevated after 5 days of probiotic treatment. The TNF-${\alpha}$ and IL-$1{\beta}$ expressions were observed from kidney and spleen. The results of this study reveal that E. faecium induces immune-responsible materials and protects olive flounder from lactococcosis.

• Fisheries and Aquatic Sciences
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• v.22 no.10
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• pp.21.1-21.7
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• 2019

Background: Lactococcus garvieae is one of the most important risk factors in the rainbow trout culture. Therefore, the purpose of this study was to identify and detect strains isolated from rainbow trout suspected of having Lactococcus garvieae using biochemical characteristics and PCR and determination of the degree of severity of isolated strains. Methods: In this study, the cause of lactococcosis in selected rainbow trout farms in Kohkilooieh and Boyerahmad province was assayed. Gram-positive and catalase-negative bacterial isolates were first obtained from selected trout fish farms using conventional biochemical tests and PCR assay. The 10-day LD₅₀ method (concentration causing 50% mortality in 10 days) was used to determine the severity of the isolated bacteria. Results: One bacterial isolate was detected from all sampled fish which confirmed as Lactococcus garvieae using a specific PCR assay based on the 16S rDNA gene by producing a single band of 1107 bp. Analysis of the rate of mortality showed that the 10-day LD₅₀ was 4.6 × 10⁵ CFU/fish. The results of this study showed that isolated bacteria had high severity for rainbow trout. The presence of bacteria in internal organs of suspected fish showed a severe systemic infection in challenged fish. Antibiogram assay also indicated that the isolated Lactococcus garvieae were resistant to some mostly used antibiotics in rainbow trout. Conclusions: According to current research, it can be concluded that the condition of lactococcosis in the studied area is not suitable, and despite the presence of disease, there is no proper action to control and prevent the disease. Unfortunately, isolated bacteria from the studied area have a very high severity compared to bacteria isolated from other regions of the country or other countries. Therefore, further investigation is needed to determine the cause of this difference and possibly in the design of the vaccine.