In vitro Antimicrobial Activity of Bacillus spp. Against Pathogenic Vibrio spp. in Black Tiger Shrimp (Penaeus monodon)

Abstract

Twenty-five isolates of Bacillus spp. from hepatopancreas of black tiger shrimp were screened for antimicrobial activity against four shrimp pathogenic Vibrio spp. (V. harveyi VHY02, V. harveyi VHG03, V. alginolyticus VA01, V. parahaemolyticus VP02) by agar well diffusion assay. Four isolates of Bacillus spp. (B17, B19, B21 and B25) were found active against all strains of Vibrio spp. and 4 isolates of Bacillus spp. (B06, B10, B13 and B22) showed some degrees of antimicrobial activities against at least one strain of Vibrio spp. The minimum inhibitory concentration (MIC) of 4 isolates of Bacillus spp. against all strains of Vibrio spp.(10⁴ cfu/ml) were determined. The MIC, at 5.0x10⁵ cfu/ml, belonged to Bacillus B17, Bacillus B21 and Bacillus 25 and at 5.0x10⁶ cfu/ml to Bacillus B19. Broth studies were also determined by culturing Bacillus B17, Bacillus B21 and Bacillus B25 in broth containing Vibrio harveyi VHG03 (10⁴ cfu/ml). The challenging experiment showed that Bacillus B17 and Bacillus B21 with 5.0x10⁷ cfu/ml were enough to completely suppress V. harveyi VHG03 within 12 hours and Bacillus B25 was only able to reduce Vibrio harveyi VHG03 lower than control. The isolated strains Bacillus B17, Bacillus B21 and Bacillus B25 could have potential against Vibrio harveyi under in vitro condition and might be useful as biological control agents in the culture of black tiger shrimp.