Calcium-dependent antibacterial activity of donkey’s milk against Salmonella

Abstract

The aim of this study was to examine the antibacterial activity of raw donkey’s milk (DM) against Salmonella Enteritidis and Salmonella Typhimurium as well as to determine the dependence of this antibacterial activity on calcium, lysozyme and lactoferrin content. Antibacterial assays were conducted in DM artificially contaminated with these Salmonellaserotypes and then incubated at 38 °C for 8 hours. Calcium concentration was found to have a strong influence on the antibacterial activity of the contaminated DM samples supplemented with CaCl2 and EDTA. The antibacterial activity of DM against the tested Salmonella strains was observed to be strongly calcium dependent, with the addition of CaCl2 to DM samples improving its antibacterial potential against both pathogens. Salmonella Enteritidis appeared to be less sensitive to the antimicrobial agents in DM than S. Typhimurium. One explanation is the calcium-dependant antibacterial activity of DM is attributable to the calcium-binding ability of its lysozyme. Lysozyme may be the main antibacterial agent, most probably via a nonenzymatic mode of action against tested Salmonella strains.