Isolation and Probiotic Characterization of Lactic Acid Bacteria from Gastrointestinal Tract of Oreochromis Spp. (Red Tilapia)

Hew, Shu Ying (2019) Isolation and Probiotic Characterization of Lactic Acid Bacteria from Gastrointestinal Tract of Oreochromis Spp. (Red Tilapia). Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Red tilapia is the second most produced freshwater fish after catfish in Malaysia as in 2017 with the production of 25,648.59 tonnes according to the annual fisheries statistics by Department of Fisheries Malaysia. Probiotics are used to improve the feed conversion ratio and growth efficacy of livestock to achieve cost effectiveness as feed is one of the major costs in aquaculture. However, the commercially available probiotics did not achieve expected efficacy as the probiotic strains are not locally isolated and target specifically for local fish species. Thus, this project aims to isolate lactic acid bacteria (LAB) from the gastrointestinal tract of local Oreochromis spp. (red tilapia) as potential probiotics for improving growth efficacy of red tilapia. Phenotypic characterization including Gram staining and catalase test were performed for colony selection. Twenty-eight colonies that were gram-positive and catalase negative were isolated and screened. Eight strains were selected for probiotic characterization. Temperature, salinity, pH and bile salt tolerance, antibiotic susceptibility and antimicrobial test were conducted. Isolated LAB grow well in 30°C and in salt concentration ranging from 0.05% to 0.20%, which is suitable for aquaculture. The percentage of survival of all strains up to five hours is more than 89% in all pH tested (ranging from pH 3 to 9) and more than 92% in the presence of bile (0.3% and 0.5%). All strains showed different antibiotic susceptibility profile. Antimicrobial properties of isolated LAB against Aeromonas hydrophila, Edwardsiella tarda and Staphylococcus aureus were carried out by using agar disk diffusion method. Six LAB strains exhibited antimicrobial properties against Edwardsiella tarda, one of the common pathogens in tilapia aquaculture. In conclusion, strain AI2 was selected as the most potential probiotic to be further explored, potentially to be incorporated with fish feed as dietary supplement and/or direct administration into water to improve water quality. Keywords: Probiotics, Lactic Acid Bacteria (LAB), Oreochromis spp. (Red tilapia), Antimicrobial