Evaluation of the antibacterial effect of the mucus extracted from the mudskipper, Periophthalmus waltoni (Koumans, 1941) from estuaries in the northwestern of the Persian Gulf

The mucus secreted from the epidermis of fish is the first line of defense against pathogens and protects them from the risk of invading pathogenic microorganisms. The purpose of this study is to investigate and compare the three factors of mucus concentration, season, and sex in order to evaluate the antibacterial properties of the secreted mucus from a mudskipper (Periophthalmus waltoni) on four strains of standard bacteria including Escherichia coli (25922), Staphylococcus aureus (6538), Bacillus subtillis (6633), and Pseudomonas aeruginosa (9027) in both hot and cold seasons. Mucus was collected from the surface of fish skin and its antibacterial activity was evaluated by disc diffusion method . Also, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined against the two bacteria that showed more sensitivity. The results showed that in both seasonal periods and in all the studied bacteria based on the concentrations (200, 100, 50, 25 mg/ml) prepared from the extracted mucus the average diameter of the growth zone diameter was increased with an increase in the extracted mucus concentration, and the Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, were the most sensitive and resistant bacteria to the extract, respectively. From the antibacterial investigations of the mucus on the standard strains based on the seasonal factor, the mucus obtained in the warm season period had higher antibacterial properties than the mucus obtained in the cold season period (p<0.05). The average diameter of the growth zone against the studied bacteria was greater in females than males, although it was not significantly different (p>0.05). The antibacterial effects of the fish mucus depended on the mucus concentrations  (200, 100, 50, 25 mg/ml) and also, the amount of mucus secretion was significantly affected by seasonal changes and gender.