Staphylococcus aureus can grow on MacConkey (very week growth) agar while bacillus can not.

Another approach is to add a penicillin disk. Bacillus are sensitive staph are usually resistant.

Use Baired Parker agar for specific growing of Staph. aureus and Bacilli can not grow on it

Try ti use Macconkey or Baired Parker agar media to eliminate Bacillus growth, but if the problem persist add Vancomycin. Staph.auteus is resistant, however Bacillus will die

It is possible to separate them using the selective media. First grow it in the MacConkey broth for 2days(Enrichment) then streak it on MacConkey agar plates. After incubation you should get good growth of red colonies of S. aureus culture.