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Abstract
Among common diseases in tilapia, popeye and hemorrhage caused by Streptococcus agalactiae bacteria are the most common, causing high mortality rates in the table fish production farms during the hot season in summer, leading to the serious economic damage. Recently, the use of bacteria that are resistant to pathogens in aquatic products has been increasingly concerned. Therefore, this study was conducted to screen Bacillus spp. strains capable of antagonizing S. agalactiae using the diffusion well method. A total of 32 S. agalactiae strains were isolated from diseased tilapia cultured in intensive rafts in An Giang, Vinh Long provinces and Ho Chi Minh city. These strains were S. agalactiae by morphological, biochemical characteristics and PCR technique. Bacillus spp. strain collection from Biotechnology Center Ho Chi Minh City (n = 60) was screened for the antagonistic activity against 12 representative S. agalactiae strains from three different geographical regions. The results showed that 18 Bacillus spp. strains had strong in vitro antagonistic activity against S. agalactiae (D > 18 mm). On the other hand, the isolation of S. agalactiae indicated a frequent occurrence of this strain circulating in the surveyed geographical regions. Therefore, control of S. agalactiae infection in tilapia by antagonistic bacteria is essential and worth of concerning.