Isolation of Components with Antimicrobial Property from the Donkey Milk: A Preliminary Study

The presence of components in donkey milk, different from lysozyme, capable of inhibiting the growth of pathogenic microorganisms was investigated. Milk was acidified, hydrolyzed with pepsin, and analyzed by HPLC. The chromatographic fractions were collected in 5 main pools that, after the removal of lysozyme, were analyzed by microelectrophoresis; antimicrobial activity was evaluated against the pathogens Bacillus cereus, Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli. Hydrolyzed milk showed a protein pattern ranging from 0.78 to 25.2 kDa. It was active against all pathogenic strains tested, with inhibition halos ranging from 4.3 mm (against E.coli) to 17.4 mm (versus E.faecalis). Among the pools collected after HPLC step, pool "b" resulted to be the most rich in protein bands, most of them with a molecular weght less than 20.4 kDa, and the most effective against all the pathogens, except against E. coli. Pool "a", was active versus E. coli and B. cereus and contained only two bands, at 0.31 and 8.3 kDa, this last band probably responsible for its antimicrobial activity and chemically different from the other ones with a similar MW present in pools "c" and "e" that did not inhibit the growth of the pathogenic strains. This finding highlights the presence of bio molecules released during proteolytic hydrolysis that may contribute to the antimicrobial activity in donkey milk and play a significant role in the host defense system.