For this purpose, approximately 50 various Gram-positive and -negative microorganisms including clinical strains of Staphylococcus aureus , Bacillus subtilis , Serratia marcescens , Escherichia coli , Proteus morganii , Micrococcus lisodeicticus , Staphylococcus epidermidis , Shigella sonnei , Salmonella typhimurium , Yersinia enterocolitica .