In many conditions, bacterial surface properties are changed as a result of variation in the growth medium and conditions. This study examined the influence of bile salt concentrations (0-0.1%) on colony morphotype, hydrophobicity, $H_2O_2$ concentration, S-layer protein production, and slpA gene expression in Lactobacillus acidophilus ATCC 4356. It was observed that two types of colonies (R and S) were in the control group and the stress condition. When the bile level increased in the medium, the amount of S type was more than the R type. A stepwise increment in the bile concentration resulted in a stepwise decline in the maximum growth rate. The results showed that hydrophobicity was increased in 0.01%-0.02% bile, but it was decreased in 0.1% bile. Treatment by bile (0.01%-0.1%) profoundly decreased $H_2O_2$ formation. S-Layer protein and slpA gene expression were also altered by the stress condition. S-Protein expression was increased in the stress condition. The slpA gene expression increased in 0.01%-0.05% bile and it decreased in 0.1% bile. However, we found that different bile salt concentrations influenced the morphology and some surface properties of L. acidophilus ATCC 4356. These changes were very different in the 0.1% bile. It appears that the bacteria respond abruptly to 0.1% bile.