Screening of Antagonistic Activity of Probiotic Bacteria

ABSTRACT: The objectives of this study were to assess the microbiological quality of Egyptian yoghurt and to investigate the antagonistic activity of some probiotic bacteria against some food borne pathogens in vitro and in yoghurt. The results indicated a poor microbiological quality of yoghurt, since the microbiological parameters recorded higher values than the admissible levels. Results from the agar spot test and well diffusion assay showed the capability of probiotic bacteria to inhibit the growth of S. aureus, E. coli O157:H7 and L. monocytogenes in vitro. Yoghurt produced from milk artificially contaminated with S. aureus (8.48 log cfu mL-1) and E. coli O157:H7 (8.3 log cfu mL-1) was used for studying the ability of L. acidophilus La-5 and B. longum ATCC15707 to inhibit the growth of such pathogens. During the refrigerated storage the counts of both pathogens decreased significantly in the probiotic yoghurt than in control one. Survival of both L. acidophilus La-5 and B. longum ATCC15707 in yoghurt was satisfactory as both bacteria remained viable at levels> 107 cfu g-1 after 15 d of storage at 4 ºC, which indicate that the yoghurt would be a suitable vehicle for probiotics