Antimicrobial activity of chicken egg white cystatin Ewelina Wesierska 1 , Yousif Saleh 2 , Tadeusz Trziszka 1, *, Wieslaw Kopec 1 , Maciej Siewinski 3 and Kamila Korzekwa 4 1 Department of Animal Products Technology, Agricultural University of Wroclaw, 25 Norwida, 50-375 Wroclaw, poland 2 1st Department of Gynecology and Obstetrics, Wroclaw Medical University, 3 Chalubin ´skiego, 50-368 Wroclaw, Poland 3 Faculty of Public Health, Medical University of Wroclaw, Bartla street nr. 5, 50-618 Wroclaw, Poland 4 Bacteriological Diagnostic Laboratory, Children Hospital in Wroclaw, Kasprowicza str. 64/66, 51-137 Wroclaw, Poland *Author for correspondence: Tel.: +48-71-3205-121, E-mail: trziszka@ozi.ar.wroc.pl Received 17 December 2003; accepted 2 June 2004 Keywords: Antibacterial activity, chicken cystatin, cysteine proteases Summary 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 (IC 50 ) was observed at cystatin concentrations in the range of 80 and 100 lg/ml, and the growth was completely inhibited at concentrations in the range of 100 and 200 lg/ml. Fifty percent growth inhibition (IC 50 ) for Staphylococcus aureus, Staphylococcus gallinarum, and Staphylococcus xylosus strains was observed at 150 and 200 lg of cystatin/ml respectively, and growth was completely inhibited at cystatin concentrations in the range of 300 and 1000 lg/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. Introduction Cystatins are physiological inhibitors of lysosomal cysteine proteases, such as cathepsins B, L, H, S and of the plant cysteine proteases: papain, actinidin and ficin. Cystatins are widely distributed in mammalian tissues and are present in body liquids. Their function is presumably to protect the organism against uncon- trolled action of endogenous and exogenous cysteine proteases (Turk & Bode 1991; Abrahamson 1994). Hens’ eggs are more and more widely used not only for direct consumption, but also as an important material in food production and in the pharmaceutical and cosmetics industries (Kijowski et al. 2000). Biolog- ically active substances contained in egg white, e.g. lysozyme, cystatin, avidin, conalbumin and ovomucin, have recently drawn much attention of researchers (Li- Chan et al. 1995; Ibrahim 1997). All cystatins are members of one evolutionary superfamily consisting of three distinct subfamilies of closely related proteins: stefins, cystatins and kininogens. The superfamily was subdivided on the basis of sequence homology and the presence and position of intradomainal disulphide linkages (Barrett et al. 1986). Cystatins are important not only in the intracellular catabolism of peptides and proteins and in the processing of prohormones and proenzymes, but also in protecting normal human tissue from malignant cells and, possibly, microorganisms including bacteria and viruses (Bjorck et al. 1989). Takahasi et al. (1994) observed that the phosphorylated rat cystatin A inhibited the growth of Staphylococcus aureus and its cysteine protease activity. Cystatin, as a substance with high inhibitory activity against cysteine proteases, has antibacterial and antiviral qualities and is a factor inhibiting the development of cancer cells. In recent years, the research on cystatin has been intensified and cystatin may be widely used in fighting cancers, paradontosis and AIDS (Cimerman et al. 1996; Hens- World Journal of Microbiology & Biotechnology 2005 21: 5964 DOI: 10.1007/s11274-004-1932-y Ó Springer 2005