Antibacterial Activities of Antibacterial Proteins/Peptides Isolated from Organs and Mucus of Clarias Gariepinus Reared at High Stocking Density

Antibacterial proteins/peptides are important parts of the innate immune system in Clarias gariepinus. To examine potential antibacterial proteins/peptides in organs and mucus of C. gariepinus, crude protein/peptide extracts were isolated with ammonium sulfate precipitation from mucus, skin, gill, suprabranchial organ and intestine. Following further extraction using Sephadex G-50 gel filtration chromatography, the proteins/peptides associated with two absorption peaks (AP1 and AP2) were pooled, respectively, and assayed for their antibacterial activities against Escherichia coli, Aeromonas hydrophila and Edwardsiella tarda. The results showed that AP1 and AP2 from all the sampled tissues and mucus at concentration of 100 mg mL-1 exhibited antibacterial activity against the tested bacterial strains. Differences in antibacterial activity were observed among sample extracts. The protein profiles of AP1 obtained by Tricine-SDS-PAGE gel showed a broad range of peptides/proteins, and molecular weight of the mutual abundant peptide obtained was about 27 kDa. Antibacterial activity of AP2 extracted from intestine was due to peptide with molecular weight of 5.5 kDa.