Evaluation of antimicrobial potential of a galactose-specific lectin in the skin mucus of african catfish (clarias gariepinus, burchell, 1822) against some aquatic microorganisms

Abstract

A galactose-specific lectin purified from the skin mucus of African catfish (Clarias gariepinus) was tested for antimicrobial activities against microbial pathogens isolated from the catfish pond water with a view to examining the involvement of the protein in the host defense mechanism. Standard methods of microbial isolation and identification were employed and disc-diffusion method was used for the anti-microbial assay. Anti-microbial evaluation of standard antibiotics ampicillin and nystatin were used as comparative study. The microbial load of the fish pond water was high, with highest total bacterial count of 7.1×10 8 CFU mL -1 and fungal count of 6.7×10 3 CFU mL -1. Twelve bacterial species and 14 fungi species were isolated and identified from the pond water. The lectin specifically agglutinated different Gram-negative bacteria, such as Aeromonas hydrophila, Alcaligenes faecalis, Klebsiella edwardsii and Vibrio metschnikovii but had no effect on Gram-positive bacteria. It inhibited strongly the growth of A. hydrophila, A. faecalis, Bacillus cereus, B. polymyxa, K. pneumoniae, K. edwardsii, Pseudomonas aeruginosa and V. metschnikovii. In the same manner, the lectin inhibited the mycelia growth of yeast, Kluyveromyces marxianus and a phytopathogenic fungus, Fusarium oxysporum. The ability of skin mucus lectin to agglutinate and inhibit the growth of bacteria and fungi will make available effective defense mechanism for the African catfish against invading microbes.