Antimicrobial activity of chicken egg white cystatin

The cysteine protease inhibitor cystatin was purified from chicken egg white and its antimicrobial activity determined for a series of pathogenic bacteria. The results indicate that Acinetobacter lwoffii, Escherichia coli, Oligella sp. and Pseudomonas aeruginosa are highly sensitive to low concentrations of cystatin, which possesses bactericidal activity. No inhibition was observed with a Citrobacter freundii strain. Fifty percent growth inhibition (IC50) was observed at cystatin concentrations in the range of 80 and 100 mug/ml, and the growth was completely inhibited at concentrations in the range of 100 and 200 mug/ml. Fifty percent growth inhibition (IC50) for Staphylococcus aureus, Staphylococcus gallinarum, and Staphylococcus xylosus strains was observed at 150 and 200 mug of cystatin/ml respectively, and growth was completely inhibited at cystatin concentrations in the range of 300 and 1000 mu g/ml. The activity of cysteine proteases was significantly decreased in the culture supernatant of microorganisms when chicken cystatin was added. In this study, we observed that chicken cystatin may be a candidate for antibacterial drug development aiming at controlling bacterial pathogens including Escherichia coli, Pseudomonas aeruginosa, and another possible application might be as a therapeutic agent for health improvement.