乳製品研究の進歩
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概要

Antibacterial Action 0f Dextran Conjugated Lysozyme against Bacteria Involved In Bovine Mastitis

Mahmoud Aminlari

Mastitis is the bacterial-induced inflammation of cow's mammary glands which results in low quality and low yield of milk, and incurs substantial economic loss to dairy industry worldwide. Treatment is possible by long acting antibiotics, but milk from such cows is not marketable until drug residues have left the cow’s system. Lysozyme is the enzyme that hydrolyses the β-glycosidic linkage of the outer peptidoglycan envelope of the cell wall of Gram positive bacteria, thereby destroying them. Antimicrobial action of lysozyme can be extended towards Gram negative bacteria by chemical modification. The aims of the present study were to conjugate chicken egg-white lysozyme with dextran and to assess the antibacterial properties of the lysozyme-dextran bioconjugate against causative agents of bacterial mastitis. Chicken egg white lysozyme was conjugated with dextran under mild Maillard-based conditions and the conjugated product purified and antibacterial activity studied (a 1:5 ratio of lysozyme: dextran, 60oC, RH79%). Degree of conjugation was followed by G 100 gel filtration chromatography and SDS-PAGE. Growth of bacteria was monitored by recording absorbance at 600 nm. The results showed that neither lysozyme nor the conjugate derivative have significant effect on the growth kinetics of Staphylococcus aureous, Listeria monocytogenes and Streptococcus agalactica. Bacillus cereus, on the other hand behaved entirely different. After 25 h the growth of this bacterium in the presence of lysozyme was reduced by 20% while the conjugated lysozyme lowered growth by 80% after 5 h. Conjugated lysozyme reduced the growth of E. coli, treatment by 50%. Growth of Klebsiella pneumonia decreased by 20% after 24 h in the presence of lysozyme and by more than 80% after 10 h in the presence of dextran-conjugated lysozyme. Taken together, the results of this study show that lysozyme-dextran conjugate may be a natural antimicrobial agent useful in pharmaceutical preparations for the treatment of bovine mastitis.