Comparative in vitro Resistance of Staphylococci to Penicillin and to Sodium Sulfathiazole ∗ †

Abstract

Discussion and Conclusions

When 68 strains of pathogenic staphylococcus were subjected to the in vitro action of sodium penicillin, 8 of the strains, or approximately 12%, were found to be quite resistant, requiring from 0.4 units per cc to 0.8 units of penicillin before growth was completely inhibited. The growth of the remaining 60 strains necessitated the following amounts of penicillin before growth was inhibited: 22 strains, or about 3276, required 0.2 units; 25 or approximately 3776, required 0.1 unit; while 12 or about 1870, failed to grow in the presence of 0.05 unit. About 28% of the strains were found to be highly resistant to the antistaphylococcic action of sodium sulfathiazole. There was no relationship between resistance to penicillin and to the sulfonamide. The evidence at hand would indicate that the mechanism whereby staphylococci become resistant to the sulfonamides is different and unrelated to the development of resistance to penicillin. 10-14

Since some strains of staphylococcus isolated from patients appear to be naturally resistant to penicillin, and yet, sensitive to sodium sulfathiazole, it would not be unreasonable to assume that a combination of therapy with penicillin and sulfathiazole might be advantageous in the management of some types of staphylococcic sepsis. Further clinical observations are necessary to substantiate this, but preliminary investigations appear to bear out this assumption.