Inhibition of Pathogenic Bacteria by Camel's Milk: Relation to Whey Lysozyme and Stage of Lactation

Abstract

Twenty (10%) of 200 milk samples collected from different individual camels inhibited growth of one or more of six pathogenic test organisms in a filter-paper disk assay. The milk samples with inhibitory properties scored zero in the California Mastitis Test. The percentages of milk samples which inhibited Clostridium perfringens, Staphylococcus aureus, Shigella dysenteriae and Salmonella typhimurium were 7.5, 4.0, 2.0 and 1%, respectively. None of the 200 samples inhibited Bacillus cereus or Escherichia coli. Five milk samples inhibited growth of two test organisms and two samples inhibited growth of three organisms. Inhibition zone diameters ranged from 13.5 mm to 22.0 mm (average of 15 mm) using a disk of 12.5 mm in diameter. The average amount of lysozyme in the whey of 58 samples of camel's milk was 288 μg/100 ml. The average lysozyme content of the 20 samples showing growth inhibition of one or more test organisms was 648 μg/100 ml, significantly higher (P<0.01) than the average in the 38 samples (62.6 μg/100 ml) that had no inhibitory effect. There was a negative correlation (r= −0.669) between lysozyme content in the whey of milk samples (y) and the stage of lactation of the camels (x) with the following regression equation: y = −2.86x + 665.8.