Antibacterial effect of postbiotics from gut bacteria of whiteleg shrimp litopeaneus vannamei against aquaculture bacterial pathogens

• Main Author: Ang, Chun Yao
• Format: Thesis
• Language: English; English
• Published: 2022
• Subjects: QR75-99.5 Bacteria
• Online Access: https://eprints.ums.edu.my/id/eprint/40696/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/40696/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/40696/

Whiteleg shrimp (Litopenaeus vannamei) aquaculture is very important industry in Sabah, but disease outbreak commonly happens. Various disease control strategies such as specific pathogen free postlarvae, tighter disease and effluent management, phage therapy, antibiotic, vaccination, passive immunization, phytobiotic, probiotic, prebiotic, synbiotic and parabiotic have been introduced but each has its own shortcomings. Thus, postbiotics are explored as an alternative disease control strategy. Crude postbiotics were extracted through ethyl acetate from gut bacteria isolates of whiteleg shrimp, namely P17 (Enterobacter sp.), P18 (Bacillus thuringiensis), P19 and P20 (Lactobacillus plantarum), P21 (Staphylococcus sp.) and P22 (Bacillus cereus). Next, the best crude postbiotics with the most antibacterial effects against aquaculture bacterial pathogens (Vibrio alginolyticus ATCC 17749, Vibrio anguillarum ATCC 19264, Vibrio parahaemolyticus SS07 and Photobacterium damselae SS16) were selected for subsequent tests. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of selected crude postbiotics against the pathogens were determined. Growth curves of V. parahaemolyticus SS07 in 1x and 2x MIC of selected crude postbiotics were determined. The effects of temperatures (40, 60, 80, 100 and 121℃) and types of buffers (acetate and phosphate-buffered saline (PBS)) on the antibacterial activities of postbiotics were determined. The antibacterial component of selected crude postbiotics was identified. Safety of the selected crude postbiotics was examined through toxicity testing on brine shrimp (Artemia). Crude postbiotics of P17, P18 and P20 were selected, and the MIC and MBC range for the selected crude postbiotics were 10-25% and 10-30%, respectively. The MIC and MBC determined enable optimum dose of postbiotics for maximum disease protection. The exponential growth of V. parahaemolyticus SS07 was suppressed at 1x and 2x MIC of the selected crude postbiotics. Antibacterial activities of the selected crude postbiotics maintained at 40-121℃, and in acetate and PBS buffers. Selected crude postbiotics were identified as organic acids. The selected crude postbiotics were toxic to Artemia sp.. However, oral administration of postbiotics through feeds might be safe. Therefore, in vivo feeding trials of postbiotics is recommended. Postbiotics have the potential as disease control strategy for whiteleg shrimp. However, optimization of the environmental conditions for postbiotics production, organic solvent extraction and purification methods are recommended for accurate future in vitro trials.