Activity of trimethoprim/sulfamethoxazole plus polymyxin B against multiresistant Stenotrophomonas 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 microgram/ml, 0.1 microgram/ml and 0.5 microgram/ml) against 30 multi-resistant strains of Stenotrophomonas maltophilia were tested. Polymyxin B at 0.01 microgram/ml modified the inhibitory activity of TMP/SMX against only 40% of strains. At 0.1 microgram/ml and 0.5 microgram/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.