Determination of biofilm and quorum sensing inhibition characteristics of microalgal extracts on some fish pathogens

In aquaculture, it is very important to keep the bacterial flora associated with the disease in production systems under control. As a result of the failure to control the bacterial flora, diseases that cause serious and great economic losses may occur. Today, antibiotics are widely used in the treatment of fish diseases. Antibiotic resistance, which emerges as a result of excessive and routine use of antibiotics, complicates the treatment of diseases. In order to prevent this situation, it is necessary to develop new and alternative methods. Inhibition of the bacterial quorum sensing and biofilm formation has emerged as an alternative treatment method that has been studied in recent years. Thus, diseases can be prevented by inhibiting the mechanisms that greatly trigger pathogenicity and increase the potency. In this study, extraction was carried out using four different solvents (methanol, ethanol, chloroform and water) from Arthrospira platensis cyanobacteria and Nannochloropsis sp. microalgae. Biofilm inhibition (antibiofilm) and quorum sensing inhibition (anti quorum sensing) properties of the extracts on Lactococcus garvieae, Aeromonas hydrophila and Yersinia ruckeri fish pathogens were investigated. As a result of the thesis study, the extracts with the strongest antibacterial effect were determined as Nannochloropsis sp. chloroform (256-512 µg/mL), A. platensis chloroform (512-1024 µg/mL) and A. platensis methanol (512-2048 µg/mL) extracts. The extracts that the most inhibited the biofilm structure formed by the bacteria were determined as chloroform extracts (at all concentrations tested between 128-4096 µg/mL). The extracts that reduced the cell surface hydrophobicity of the bacteria the most were chloroform (at all concentrations tested between 128-4096 µg/mL) extracts. Nannochloropsis sp. ethanol (2048 µg/mL) and Nannochloropsis sp. methanol (2048 µg/mL) extracts were found to be the most effective extracts in the analysis of exopolysaccharides degradation produced by bacteria. Nannochloropsis sp. chloroform (128-256 µg/mL), Nannochloropsis sp. methanol (2048 µg/mL) and Nannochloropsis sp. ethanol (2048 µg/mL) extracts were determined as the extracts that inhibited the biofilm structures formed on the glass surface the most. The extracts that have been most effective on mature biofilm structure in the analysis of biofilm eradication are chloroform extracts (128-512 µg/mL) and methanol extracts (512-2048 µg/mL) when viewed under a light microscope. In the inhibition studies of QS molecules, the most effective extracts inhibiting violacein pigment produced by Chromobacterium violaceum (ATCC 12472) were ethanol (1024-2048 µg/mL), methanol (1024-2048 µg/mL) and water (1024-4096 µg/mL) extracts. In the study using Agrobacterium tumefaciens (NT1), it was determined that the extracts with the highest inhibition of QS molecules were ethanol (1024-4096 µg/mL) and chloroform (64-512 µg/mL) extracts. As a result, it was determined that the extracts obtained in this thesis study had antibacterial, antibiofilm and QS inhibition activities.