Ex vivo evaluation of the polysaccharide-encapsulated, host-derived microbial compositions on the gut microbiota of jade perch (scortum barcoo)

• Main Authors: Li, Wenrui, Wong, Liqi, Thi, Sara Swa, Wang, Yulan, Conway, Lynne Patricia, Loo, Joachim Say Chye
• Other Authors: Interdisciplinary Graduate School (IGS)
• Format: Conference or Workshop Item
• Language: English
• Published: 2023
• Subjects: Science::Biological sciences::Microbiology::Bacteria; Engineering::Materials::Biomaterials; Probiotic Encapsulation; Polysaccharides; Ex Vivo Model; Short Chain Fatty Acids; Fish Gut Microbiota
• Online Access: https://hdl.handle.net/10356/166580; https://probiotic-conference.net/; https://probiotic-conference.net/proceedings/
• Institution: Nanyang Technological University

Probiotics have been recognized as a bio-control measure in aquaculture against bacterial infections, especially with the surge of antibiotic-resistant pathogens. To fully exert the benefits of host-derived probiotics, which are well adapted to prevailing environmental conditions, microencapsulation is often needed to prevent them from gastric acidity, storage, and feed preparation processes before reaching the targeted sites and releasing in a desired manner. Common encapsulants include polysaccharides and proteins, immobilizing probiotics in a 3D matrix to maintain their viability and effectiveness. It is worth noticing that some of these encapsulants are seaweed-derived, which can be viable candidates as prebiotics when served as dietary supplements. Therefore, this work evaluated how four common polysaccharide encapsulants, alginate, carrageenan, xanthan, and gum arabic, can be utilized to modulate the host gut microbiota in an ex vivo model. Alginate and kappa-carrageenan were shortlisted for subsequent probiotic encapsulation based on their fermentability to produce short-chain fatty acids (SCFAs), which are energy sources for intestinal epithelial cells, and the bacterial composition change in the gut microflora after the co-incubation with the fish gut suspensions. Alginate is the most common encapsulant for probiotic encapsulation due to its ability to gel with di-valent ions to provide bacteria with good gastric protection and a lack of toxicity. Kappa-carrageenan can crosslink with mono-valent ions, and it produced the most abundant SCFAs and could not be selectively utilized by pathogenic bacteria. Both needle extrusion and spray drying were explored as encapsulation techniques. Extrusion is easy to set up and mild to bacteria. Extrusion parameters, including the needle size, the polysaccharide concentration, the flow rate, and the extrusion temperature, were optimized to yield microparticles with sufficient gastric protection. The survivability of the probiotics that underwent the simulated gastric fluid remained at the same 8 Log CFU/g magnitude as before the challenge, while no survival was found for naked bacteria. The robust protection of needle-extruded particles was accompanied by difficulty releasing bacteria in the intestine, with only around 5 Log CFU/g could be released in 2 hours. Considering fish’s short digestion time, needle extrusion may not be optimal for probiotic delivery in aquaculture. Spray drying was adopted to resolve the release problem. The host-derived strain can withstand the spray drying condition and readily release in the simulated intestinal fluid with uncompromised protection in the gastric environment. The ex vivo co-incubation study confirmed that introducing this encapsulated host-derived isolate could effectively suppress the growth of Aeromonas. Future work includes the in vivo challenge test in jade perch to assess whether manipulating the host gut microbiota through host-derived probiotic supplementation can increase disease resistance and how the bacteria persist in their native environment.