Concerning the antimicrobial activities of some probiotics bacteria Lactobacillus acidophilus P109, Lactobacillus plantarum P164, E. durans P174 and B. longum CHRS using an agar well-diffusion as In Vitro assay against selected isolates of Pseudomonas fluorescens, Bacillus cereus, Enterococcus fecalis and Staphylococcus aureus, indicated that B. longum CHRS appeared to have antimicrobial activity against these isolates. B. longum CHRS was injected with and without Ps. fluorescens in Domiati cheese during manufacturing as In Vivo experiment, results revealed that this strain of probiotic bacteria was reduced the count of Ps. fluorescens, while the chemical composition showed reduce production of soluble nitrogen, which has relation with the decomposition of protein as well as led to reduced volatile fatty acids, which refers to the decomposition of fat as a result of antimicrobial activity of B. longum against Ps. fluorescens.