Activity of trimethoprim/ sulfamethoxazole plus polymyxin B against multiresistantStenotrophomonas maltophilia

The inhibitory activity of eight antibiotics and the inhibitory and bactericidal activities of combinations of trimethoprim/sulfamethoxazole (TMP/SMX) plus three fixed concentrations of polymyxin B (0.01 μg/ml, 0.1 μg/ml and 0.5 μg/ml) against 30 multiresistant strains ofStenotrophomonas maltophilia were tested. Polymyxin B at 0.01 μg/ml modified the inhibitory activity of TMP/SMX against only 40% of strains. At 0.1 μg/ml and 0.5 μg/ml, polymyxin B enhanced the inhibitory activity of TMP/SMX activity against all strains. Polymyxin B enhanced the bactericidal activity of TMP/SMX only at concentrations near the minimum inhibitory concentration of polymyxin B alone.