The present invention features an antibacterial composition comprising 1) a composition A comprising polymyxin B and trimethoprim; and 2) an antibiotic agent selected from the group consisting of rifampicin, rifabutin, rifapentine, rifaximin, pefloxacin mesylate, sparfloxacin, sarafloxacin HCl, tobramycin, lomefloxacin, besifloxacin, danofloxacin mesylate, enrofloxacin, nadifloxacin and clinafloxacin, a topical pharmaceutical thereof, and a method of treating bacterial infections using mixtures of 1 and 2.