Inhibition of food-borne bacteria by thermo-chemically modified egg white lysozyme

This study investigates the effect of different concentrations (0.50 to 1.50%) of thermo-chemically modified lysozyme on the growth of selected bacteria, that is, Gram-negative Pseudomonas fragi, Pseudomonas fluorescens, Escherichia coli, Proteus mirabilis and Gram-positive Listeria innocua, Leuconostoc mesenteroides in nutrient broth. The content of lysozyme polymeric forms after modification was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The dimer and trimer fractions of the modified lysozyme were 35.9 and 33.1%, respectively. The modified lysozyme exhibited higher surface hydrophobicity and lower hydrolytic activity than monomer. No inhibitory action of lysozyme monomer was observed in relation to the tested Gram-negative bacterial strains. The application of modified lysozyme at a concentration of 0.75% and higher, caused a complete reduction of bacterial counts as early as after 1 h incubation in case of P. fragi, P. fluorescens and E. coli or after 6 h incubation in case of P. mirabilis. After 6 h incubation both in samples with an addition of monomer and those with modified lysozyme a complete growth inhibition of L. mesenteroides was recorded. Modified lysozyme showed a stronger antibacterial activity against L. innocua than native lysozyme. Conducted analyses indicate that changes in the structure of enzyme molecules leads to an increase in the antibacterial action mainly towards Gram-negative bacteria. Key words: Antibacterial activity, modified lysozyme.