Antimicrobial Activity of Duck Egg Lysozyme against Salmonella enteritidis

The objective of the study was to investigate antimicrobial activity of native and reduced forms of duck lysozyme (dLz) against Salmonella enteritidis. Moreover, antimicrobial activity of dLz was compared with chicken lysozyme (cLz). The purified dLz was reduced with dithiothreitol. Free SH groups of reduced dLz were trapped with iodoacetamide. Lytic activity against Micrococcus luteus of reduced dLz decreased according to a period of reduction time. Whereas, reduction of dLz enhanced antimicrobial activity against S. enteritidis IFO3313 and other S. enteritidis found in contaminated food. The antimicrobial activity of reduced dLz depended on the time of reduction as 1.5 h reduction showed highest antimicrobial activity. Incubation of lysozyme with S. enteritidis at various temperatures showed that the optimum temperature for antimicrobial activity of reduced Lz is 45-49 ̊C. The presence of polyphosphate (0.05-0.10%) enhanced the antimicrobial effect of reduced dLz. On the other hand, addition of NaCl (0.05-0.10 M), glucose (10%), sucrose (10%) and bovine serum albumin (0.5-1.0%) decreased the antimicrobial activity of reduced dLz. Meanwhile, glycine (0-0.5%) did not show any effect on reduced dLz inhibitory activity. Combination of lactoferrin (0.1 mg/ml) and reduced dLz (0.1 mg/ml) showed a synergistic effect. In all conditions, dLz showed higher activity than cLz in both native and reduced forms. The result of the study indicated that reduced dLz trends to be a more efficient antimicrobial agent against S. enteritidis. To achieve the highest sufficiency, the essential roles of food components and incubation temperature should be concerned in reduced dLz application.