This study was carried out to determine the effect of various factors influencing the antibacterial activity of fermented milk with Bifidobacterium spp. 420 (bifidus) and with L. acidophilus 145 (acidophilus) against eight test bacteria, viz Staphylococcus aureus, Escherichia coli 0157:H7, Pseudomonas fluorescens, Klebsiella pneumoniae, Enterobacter cloacae, Listeria monocytogenes, Serratia marcescens and Salmonella infantis were determined. The agar diffusion technique was used to determine the antibacterial activity. There was a significant variation (P≤0.05) in the antibacterial activity of bifidus and acidophilus made of various types of milk (buffaloes, cows, goats, ewes and camels' milk). Goats and camels fermented milk had a greater antibacterial activity than control (MRS medium) and other types of milk. The Gram-positive bacteria (L. monocytogenes and Staphylococcus aureus) took an opposite trend compared with tested Gramnegative pathogens. Antibacterial activity against Gram-positive were higher at pH 5 and pH 4.8 than pH 4.6, while antibacterial activity increased against tested Gramnegative pathogens at lower pH values. Statistically, no significant differences were observed between control and 15% sucrose concentration against all tested pathogens, except Escherichia coli 0157:H7 and Serratia marcescens, which were significant inhibition at 15% sucrose. Generally, there were not statistically significant differences between antibacterial activity in control and 0.3 % sodium chloride (NaCl) or between 0.6 and 0.9 % NaCl, however, 0.6 and 0.9% resulted in significant inhibition against the tested pathogens than 0.3 % NaCl.
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