Biochemical, biological characteristics and antibacterial activity of glycoprotein extracted from the epidermal mucus of African catfish (Clarias gariepinus).

Catfish glycoprotein (CFG) was extracted from the cutaneous mucus of Egyptian catfish by ammonium sulphate precipitation and purified on gel filtration column (sephadex G-50). After purification, CFG produced one band on SDS-PAGE (22 kDa). Urea-PAGE and the pH-solubility of CFG indicated its positive charge (IEP 8). CFG contained 12 saccharides. FTIR spectrum shows 3 groups of bands at 1800-2900, 1100-1700 and 700-1100 cm-1. CFG exhibited antibacterial activity against 9 pathogenic bacteria with low MIC (50 μg/mL), where two Gram+ bacteria, i.e.; Streptococcus pyogenes (St. pyogenes) and Listeria ivanovii (L. ivanovii) were the most sensitive. The growth curves of the bacteria subjected to 1 MIC of CFG during 30 h showed general growth inhibition, particularly in case of Gram- bacteria such as E. coli. TEM images showed evidently reduced relative content of the intact cells and clear incurred cellular malformations. Combining CFG with specific antibiotic at equal ratios induced synergistic antibacterial actions, amounting to 40% of the mathematical sum of the combination. Substituting the antibiotic chloramphenicol with gradual increasing ratios of CFG of its starting concentration (30 μg/mL), produced proportionally bigger antibacterial actions against St. pyogenes growth and increasing synergistic effect up to 37% at 80% of CFG substitution.