Biological Research Laboratory, Tanabe Seiyaku Co., Ltd. Bactericidal activities of SMX, TMP and combinations of SMX-TMP in vitro were investigated with several strains of Staphylococcus aureus and Escherichia coli. Complete viable counts were performed in cultures containing the drugs singly and together according to the chequer-board titration method and bactericidal action was estimated by a decreased rate of survived bacteria.
In the combination, significant bactericidal effects were exerted by the far lower concentrations than the MIC of each drug alone, although they, when acting singly, did not totally eliminate viability. The synergism on bactericidal effect was found to be most pronounced with the combination equal to the ratio of MIC of either drug alone.
