Abstract:
Six bacterial strains producing antibacterial substance against two marine pathogens, Aeromonas hydrophila and Vibrio harveyi, were isolated from shrimp pond-water. Among those strains, a strain BK9 exhibited the highest antibacterial activity. Production of the antibacterial substance from strain BK9 followed typical kinetics of primary metabolite synthesis. The strain BK9 was identified as a Bacillus licheniformis using API 50 CHB. Antibacterial substance was partially purified with two steps: 0-28% saturation (NH4)2SO4 and sephadex G-50 column. A molecular weight of the substance was 7.217 kDa. Its antibacterial activity exhibited a broad spectrum against Gram-positive and Gram-negative bacteria. The antibacterial activity was not destroyed by treatment with some proteolytic enzymes. The antibacterial substance of BK9 was heat stable and remained active over a pH range from 2-12 and 6-9 against A. hydrophila and Vibrio harveyi, respectivly. Mode of action of the antibacterial substance was lytic activity. Comparison of antibacterial activity of partial purify substance from a strain BK9 with that of chloramphenicol and erythromycin was also carried out in this work.