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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Antimicrobial activity of the biopolymer chitosan against Streptococcus iniae

Author
item Beck, Benjamin
item Aksoy, Mediha
item Shoemaker, Craig
item Fuller, Adam
item Peatman, Eric - AUBURN UNIVERSITY

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2018
Publication Date: 2/11/2019
Citation: Beck, B.H., Aksoy, M., Shoemaker, C.A., Fuller, S.A., Peatman, E. 2019. Antimicrobial activity of the biopolymer chitosan against Streptococcus iniae. Journal of Fish Diseases. 42:371-377.

Interpretive Summary: The antimicrobial activity and mode of action of chitosan, a natural biopolymer, was evaluated against Streptococcus iniae, a pathogenic bacteria that is lethal to fish worldwide. Chitosan inhibited the growth of S. iniae at concentrations of 0.1% and above and was lethal at a concentration of 0.4% and higher. The mechanism of antibacterial activity of chitosan at the inhibitory level of bacterial growth appears to hinge upon the interaction between chitosan and the oppositely-charged bacterial surface. This interplay causes agglutination (e.g., clumping), which was readily observed with the naked eye. After interacting with the cell surface, a release of intracellular ATP from the bacteria was documented, which suggests that chitosan disrupts the bacterial cell causing leakage of essential internal components and ultimately cell death. Results suggest chitosan may be worth evaluating as a natural alternative to antibiotic against S. iniae infection of fish.

Technical Abstract: The antimicrobial activity and mode of action of chitosan was evaluated against Streptococcus iniae, a pathogenic Gram-positive bacteria of fish worldwide. Cell proliferation kinetics were examined following exposure to varying concentrations of chitosan. The action of chitosan on S. iniae was also investigated by measuring agglutination activity, conductivity, and extracellular and intracellular bacterial adenosine triphosphate (ATP) levels. Chitosan exhibited antibacterial activity against S. iniae at concentrations of 0.1% and above and was lethal at a concentration of 0.4% and higher. The mechanism of antibacterial activity of chitosan at the inhibitory level of bacterial growth appears to hinge upon the interaction between chitosan and the oppositely-charged bacterial surface. This interplay causes agglutination, which was readily observed grossly and microscopically. After interacting with the cell surface via adsorption an efflux of intracellular ATP was documented, which suggests that chitosan disrupts the bacterial cell causing leakage of cytosolic contents and ultimately cell death. Results suggest chitosan may be worth evaluating as a natural alternative to antibiotic against S. iniae infection of fish.