Susceptibility of Chloramphenicol-Resistant Strains of Salmonella Typhi to Trimethoprim/Sulfamethoxazole
The resistance of certain strains of Salmonella typhi to chloramphenicol is due to an R-factor which also confers resistance to sulfonamides. Typhoid fever, caused by these strains, responds to treatment with TMP/SMX, but, because of their resistance to SMX, the question arises as to whether the sulfonamide contributes to the efficacy of the treatment.
With each of the strains examined the MIC of TMP was halved by the presence of SMX and the zones of inhibition produced by a disc containing TMP were increased by the addition of SMX. Also, with each of the strains, the decreases produced in the growth rate by sub-inhibitory concentrations of TMP were increased by the presence of SMX. In experimental infections of mice, the protection afforded by TMP was increased by SMX.
KeywordsMinimum Inhibitory Concentration Typhoid Fever Dihydrofolate Reductase Aminobenzoic Acid Tetrahydrofolic Acid
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