BIOCONTROL OF β – HAEMOLYTIC AEROMONAS HYDROPHILA INFECTION IN LABEO ROHITA USING ANTAGONISTIC BACTERIUM PSEUDOMONAS AERUGINOSA FARP72

Pseudomonas aeruginosa FARP72 was isolated from the skin mucus of freshwater catfish (Clarias batrachus) as a potent antagonistic bacterium. Efforts have made to assess the antagonistic activity against potential fish and human bacterial pathogens in vitro. Antagonistic effects were confirmed by cross-streaking method against pathogenic bacteria such as Aeromonas hydrophila, Bacillus subtilis, Bacillus amylolequifasciens, Escherichia coli, Edwardsiella tarda, Klebsiella pneumoniae, Enterohaemorrhagic Escherichia coli (EHEC), Pseudomonas aeruginosa, Salmonella Typhi, beta haemolytic Streptococcus, Staphylococcus aureus ATCC12598and Vibrio cholera. The LD₅₀ value of Pseudomonas aeruginosaFARP72 and β-haemolytic Aeromonas hydrophila N₁₀P were calculated to be >5.65×10¹⁰ cells/ fish and 2.37×10⁸ cells/fish, which proved them to be non-pathogenic and moderate pathogenic respectively. In biocontrol experiment, the Labeo rohita stocks which received a first 15 min dip in Pseudomonas aeruginosaFARP72 suspension containing 1×10⁷cells/ml followed by another dip in β- haemolytic Aeromonas hydrophila suspension containing 1×10⁵ cells/ml for 15 min and subsequently cohabited with healthy Labeo rohita showed 37% mortality; while 75% of the fish died when treated only with β- haemolytic Aeromonas hydrophila suspension containing 1×10⁵ cells/ml in 30 days of post-challenge. The results suggest that Pseudomonas aeruginosaFARP72 can be a substitute to the commercially available and indiscriminately used common antibiotics, reducing the attachment of Aeromonas hydrophila and development of infection and disease outbreaks. Judicious use would help overcome the problems of developing antibiotic resistant pathogenic strains, side effects of antibiotics etc. without causing any environmental pollution, reducing stress and better disease management and ensuring its practical approach for betterment of animal life.