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Study: Lactic acid probiotic doubled survival against pathogen

Illustrative photo of juvenile rainbow trout. Fish given a probiotic containing a man-made lactic acid bacteria that stimulates an immune response had a much higher survival rate when challenged with F. psychrophilum. Photo: Salmonexpert.cl.
Illustrative photo of juvenile rainbow trout. Fish given a probiotic containing a man-made lactic acid bacteria that stimulates an immune response had a much higher survival rate when challenged with F. psychrophilum. Photo: Salmonexpert.cl.

Rainbow trout that were given a laboratory-made lactic acid bacterium producing interferon gamma (IFNγ) had better survival rates when challenged with the pathogen Flavobacterium psychrophilum, Chilean researchers have reported.

Varied research has associated and confirmed the role of INFγ – a member of the class of proteins called cytokines - as having antiviral properties, and other laboratory work suggests that IFNγ could also have antibacterial properties in salmonids.

However, the application of IFNγ has been limited due to the lack of a viable delivery vehicle compatible with fish physiology, according to scientists who evaluated the use of the recombinant lactic acid bacterium (LAB) Lactococcus lactis (MT009), which stimulates the production of IFNγ when administered as a probiotic. 

The researchers also explored its role against bacterial infection by F. psychrophilum and the ability to stimulate the systemic immune response after oral administration.

Immune response

The results of tests on fish showed an increase in the immune response cytokines IL-6, IFNγ and IL-12 in spleen and kidney, in addition to stimulating the activity of the antimicrobial enzyme lysozyme in serum, after oral administration in rainbow trout.

Regarding the challenge with F. psychrophilum, the scientists showed that on day 17 post-infection the fish treated with MT009 presented a survival of 73.3% compared to 26.6% and 36.6% in the control groups.

“The challenge tests indicated that the administration of the IFNγ-producing probiotic doubled survival in fish infected with F. psychrophilum. The Relative Percentage Survival (RPS) of fish treated with MT009 corresponded to 57.8% with respect to fish without treatment,” the researchers explained.

The study is published in the journal Frontiers in Immunology. Read the full study, Oral administration of Lactococcus lactis producing Interferon Type II enhances the immune response against bacterial pathogens in rainbow trouthere.