Putative Bacterial Flora Assessment in Juvenile Litopenaeus vannamei as Probiotics by using Antibacterial Activity Tests

摘要

The objective of this study was to find an effective probiotic of putative bacterial flora, using in vitro antagonism test in Litopenaeus vannamei. Twelve groups of putative bacterial flora, isolated from juvenile Litopenaeus vannameiPersian Gulf Jihad Agriculture Center Hatchery unit, were used for antibacterial investigation against six pathogenic bacteria including Vibrio parahaemolyticus, Aeromonas hydrophila, Pseudomonas aeroginosa, Escherichia coli, Salmonella sp. and Vibrio cholerae. The threegroups of putative bacteria {Bacillus sp., Micrococcus sp. and Corynebacteriumsp.), collectively showed antagonistic activity against the six pathogens. Bacillus sp. showed greatest inhibition of pathogens both in well and disc diffusion assays. Bacillus sp. also inhibited all six pathogens tested by the cross-streak method. Addition of 10 ml of cell- free supernatant of Bacillus sp. to pathogens resulted in complete suppression within 12 h. Maximum growth and maximum zone of inhibition (16 mm), against A. hydrophila were accrued at pH 8. Very slow growth was observed at pH 6 and pH 9. There was no growth at pH 4 and pH 5. Maximum growth was observed at 30 "C and 37 °C with maximum production of the antibacterial component. TSB media with 1% NaCl wasoptimum for growth and the zone of inhibition was 15 mm. The culture reached a stationary phase at 12 h but maximum antibacterial activity was observed only at 30 h. These results suggest that Bacillussp. has potential applications for control of pathogenic bacteria in aquaculture systems.