In vitro Additive Effect of Nitrofurantoin Combined with Trimethoprim-Sulfamethoxazole Against Serratia marcescens

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Abstract
The combination of nitrofurantoin (NF) plus trimethoprim-sulfamethoxazole (TMP-SMZ) was found to be additively effective against all of 12 clinical isolates of Serratia marcescens that represented 7 nosocomially significant strains, some of which were multiple-drug-resistant. All isolates were resistant against NF; minimal inhibitory concentrations (MICs) ranged from 320 to 1,280 μg NF/ml. The isolates were inhibited by TMP-SMZ concentrations ranging from 0.03 μg TMP + 0.57 μg SMZ/ml to 8 μg TMP + 152 μg SMZ/ml. Significantly, NF combined with TMP-SMZ proved effective against isolates with decreased susceptibility to TMP-SMZ as well. The observed in vitro additive effect of NF + TMP-SMZ might prove of clinical relevance with respect to the chemotherapy of hospital-acquired urinary tract infections due to multiple-drug-resistant strains of S. marcescens.