This project was conducted to evaluate the activity of S-layer proteinsisolated from Lactobacillus in comparison with the activity of concentrated filtrate of Lactobacillus against some pathogenic microorganisms and against tumor cell lines in vitro. Twelve isolates of Lactobacillus spp. obtained from, vinegar, human milk, cow milk, yoghurt and vagina, were used to detect the S-layer protein (Slp) by Sodium Dodecyl Sulfate-Polyacrylamide gel electrophoresis (SDSPAGE) then extracted it by excised the Slp pand and treated with 6M guanidine hydrochloride (G-HCl) to eluted the protein from gel. The Molecular weights (MW) of Slps were estimated between (37-63 kDa) depending on the Lactobacillus species. The concentrations of Slp were estimated by using a Kit based on the Biuret method. One isolate of each of Lactobacillus acidophilus and Lactobacillus casei, were selected depending on the MW and concentrations of S-layer proteins. The inhibitory effect of Lb. acidophilus and Lb. casei was determined against pathogenic microorganism; Pseudomonas aeruginosa , Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, and Candida albicans on solid and liquid MRS media. Results revealed that less inhibitory activity against tested microorganisms was detected on the solid medium, compared to the liquid one. Greatest inhibitory effect of L. acidophilus and L. casei was appeared against P. aeruginosa when the zone of inhibition reached to 24 and 22 mm, respectively. It appeared that the inhibitory effect of L. acidophilus was more than that of L. casei against most of tested microorganisms, while S-layer proteins have no effect against pathogenic microorganisms Minimum inhibitory concentrations (MICs) of Lb. spp. Concentrated filtrates were determined. Results showed 40% and 50% of the concentrated filtrate of both Lactobacilli were the MIC for P. aeruginosa, E. coli, respectively, where as MIC for Sal. typhimurium and C. albicans it was 60%, while 60% and 50% of L. acidophilus and L. casei respectively, were MIC against Staph. aureus. At such MIC,s of Lb. spp., adhesion of E. coli and Staph. aureus to the uroepithelial cells was minimized when the average decreases recorded were (5-12) and (4-9) bacteria/cell after they were (50-60) and (29-35) bacteria/cell, respectively. Adhesion of E. coli and Staph. aureus to the uroepithelial cells was also decreased by S-layer proteins with average decreased (3-9) bacteria/cell for both tested bacteria. When the cytotoxic activity of S-layer proteins and Lactobacillus concentrated filtrate by using different concentrations (1000, 500, 250, 125, 62.5 and 31.25 μg/ml) was applied against two tumor cell lines (RD and L20B) and incubated for 48 hr., results confirmed that all extracts (S- layer proteins and filtrate) have cytotoxic effects. Moreover, Lactobacillus concentrated filtrate had the highest significant cytotoxic effect on growth of both tumor cell lines when compared with S-layer proteins.
