The Correlation between the Inhibition of Drug Resistance and Synergism in Streptomycin and Penicillin

Abstract

Using Staphylococcus aureus, growth in a casein hydrolysate medium was measured turbidimetrically. Increase in drug resistance was estimated after 48 hrs. of growth at 37[degree]C. After 48 hrs. of growth in the resp. drugs, S. aureus rapidly became resistant to streptomycin, less rapidly resistant to penicillin and developed no resistance to sulfa-diazine. The greater the partially inhibitory conc. of streptomycin and penicillin, the greater the increase in the rate of development of resistance. Sulfadiazine when added to the streptomycin media was far more effective as a synergist and inhibitor of streptomycin resistance than was penicillin. Low concs. of streptomycin, penicillin, and sulfadiazine when combined were effective in inhibiting bacterial multiplication and prevented the development of drug resistance to all 3 drugs. The results are interpreted on the basis of the selection and inhibition of resistant variants.