Screening of potential probiotic bacteria from catfish (Clarias batracus) and its antibacterial activity

Probiotic bacteria have an essential role in increasing fish and shrimp production in aquaculture. Probiotics also provide many benefits including increasing Food Conversion Ratio (FCR), enhancing the immune system, increasing the digestibility of feed and against pathogenic bacteria that cause disease. Many studies have been conducted to explore the fish probiotic candidate bacteria source. The purpose of this study was to obtain candidate for probiotic bacteria isolated from catfish intestines. Potential probiotic is determined on the basis of proteolytic and antibacterial activity against pathogenic bacteria. Probiotic candidate bacteria were isolated using de Man Rogosa and Sharpe Agar (MRSA) + 1% CaCO3 and then incubated at 30^oC for 3-6 days. Twelve growth colonies produced acid. Before 16s rDNA analysis, gram staining and catalase assay were performed. The results of the analysis showed that the probiotic candidate was identified as Bacillus velezensis UBL2 with 99.8% identical to Bacillus valezensis R1.16. It has proteolytic activity and antibacterial activity on gram positive and gram-negative pathogenic bacteria. Hence, B. velezensis UBL2 is a potential candidate for probiotic.