Do you prepare it from colistin sulfate powder + distilled water following the equation c1 v1 = c2 v2 then we can mix it with McConkey agar for the isolation of colistin-resistant Gram-negative bacteria.
See our article.in vitro activity of colitin in combinations with imipenem ciprofloxacin and Amikacin against miltiresistants Pseudomonas and Acinetobacter