The Susceptibility of Serratia marcescens to Sulfamethoxazole, Trimethoprim, and Trimethoprim-Sulfamethoxazole

Abstract

The sensitivities of strains of Serratia marcescens isolated from clinical specimens, to trimethoprim (TMP), sulfamethoxazole (SMZ), and to a combination of the two drugs (trimethoprim-sulfamethoxazole) were examined. All strains were sensitive to TMP (MICs, 0.1-1 µg/ml) with varying degrees of sensitivity to SMZ (MICs, ≥ 1.0 µg/ml). Potentiation of antibacterial activity of the two drugs together was indicated by the larger clear zones of inhibition around the combination disk and by results of checkerboard titrations of combinations of the two drugs. Small colonies were present in many of the zones around the TMP and SMZ disks on Mueller-Hinton agar and sensitivity test agar (Wellcome), with and without 5% lysed horse blood.