Novel antibacterial peptides derived from hen egg lysozyme.

Hen egg white lysozyme is well known as a natural antimicrobial protein. It has attracted considerable interest as a natural food preservative as well. However, its lytic activity is limited to certain Gram-positive bacteria and is less effective against Gram-negative bacteria, including foodborne pathogens.

There have been many attempts to modify the lytic activity of lysozyme by using chemical or genetic engineering techniques. Improving the spectrum of lysozyme activity is important for food applications. Toward this end, Canadian researchers have discovered new antibacterial peptides from the enzymatic hydrolysis of lysozyme. Their goal was to enhance the microbicidal activity of lysozyme and to study the structure-function relationships of these antibacterial peptides. Their findings open up new opportunities for using lysozymes as novel natural antimicrobial agents.

The scientists performed an enzymatic hydrolysis of lysozyme using pepsin and trypsin. They analyzed the molecular mass of the digests. Antimicrobial assays were carried out using E. coli K12 and S. aureus. Lysozyme activity was determined by the lysis of M. lysodeiktilus cells. The investigators used reverse-phase high-performance liquid chromatography to characterize the antibacterial peptides.

Lysozyme was digested by pepsin to less than 5 kDa, while trypsin was partially digested. Smaller peptides of less than1 kDa were produced by the combination of both enzymes. Peptic digests of lysozyme completely lost enzyme activity, but they exhibited strong bactericidal activity against both Gram-negative and Gram-positive bacteria.

Furthermore, smaller peptides released by pepsin and trypsin digests enhanced microbicidal activity. Scanning electron microscopy revealed that the cell membranes of both bacteria were damaged by these peptides. These peptides probably have a different mechanism of action than native lysozyme. It appears that hen egg white lysozyme contains unique peptide sequences that can induce strong non-enzymatic microbicidal activity, which is released by enzymatic hydrolysis.

Further information. Yoshinori Mine, Department of Food Science, University of Guelph, Guelph, Ontario N1G2W1, Canada; phone: [phone]; fax: [phone]; email: [e-mail].