The survival of Staphylococcus aureus in the acidophilus yoghurt (AY) was evaluated during the production and cold storage. 21 acidophilus yoghurt samples were prepared with traditional yoghurt culture (Streptococcus thermophiles & Lactobacillus bulgaricus) with Lactobacillus acidophilus and inoculated with 10 6 cfu/ml S. aureus and stored for 21 days at 4 o C. Samples were taken at zero time (fresh samples), 3, 5, 7, 10, 14 and 21 days for titratable acidity, culture starters' counts and S. aureus count. The results revealed that the titratable acidity% of AY was increased and reached 0.72, 0.78, 0.83, 0.87, 0.89, 1.02 and 1.45% at zero time, 3, 5, 7, 10, 14, and 21 days of storage, respectively, while the population of S. aureus reached 6.10 and 3.70 log10cfu/g at zero time and 3 rd day of storage, respectively and became non-detectable level in 5 th days of storage. The count of all starter cultures (S. thermophiles+ L. bulgaricus+ L. acidophilus) in acidophilus yoghurt increased during the fermentation and cold storage, S.

Antagonistic activity of Bifidobacterium bifidum against Listeria monocytogenes during the production and storage of Traditional yoghurt (TY) (Streptococcus thermophiles+ Lactobacillus bulgaricus) and Bifidus yoghurt (BY) samples (Streptococcus thermophiles+ Lactobacillus bulgaricus+ Bifidobacterium bifidum). Traditional & Bifidus yoghurt samples were inoculated with 10 6 cfu/g L. monocytogenes and stored for 21 days at 4±1 o C. Samples were taken at zero time (fresh samples) then after 3, 5, 7, 10, 14 and 21 days of storage for titratable acidity measurement and bacterial count of the culture starters and L. monocytogenes counts. The results revealed that the titratable acidity of TY & BY was increased during the 21 days of storage, while the population of L. monocytogenes became non-detectable level in 10 th days of storage in BY and still detected in TY till the day 14th of storage and became 2.20± 0.31 log10 cfu/g. The count of all starter cultures (S. thermophiles+ Lb. bulgaricus+ B. bifidum) in both yoghurts increased during the fermentation and cold storage and remained stable with values >6 log10 cfu/g throughout the storage period at 4±1°C.