The antimicrobial activity of donkey milk and its microflora changes during storage

The antimicrobial activity of donkey milk was initially scanned against nine microorganisms using agar diffusion assay, and was further investigated via in situ inhibition by monitoring the growth of Salmonella choleraesuis (CGMCC 1.1859) and Shigella dysenteriae (CGMCC 1.1869) in it. The changes of microflora of donkey milk during prolonged storage at 4 and 20 °C were also studied. The results of the agar diffusion showed that S. choleraesuis and S. dysenteriae were the most sensitive strains towards the antimicrobial activity of donkey milk. In situ test revealed that the donkey milk exerted a definite bactericidal activity against S. dysenteriae and the viable counts decreased to below detectable level in a 1-ml sample at 20 °C. In the microbiological flora analysis, initial raw donkey milk contained a low microbial content. At 20 °C, lactic acid bacteria, coliforms and fungi grew well in donkey milk to give a total number of 6.66 log cfu/ml, 5.88 and 2.95, respectively, after 24 h storage. At 4 °C, no significant changes of microflora were observed after 96 h except coliforms which gave an 1 log increase.