The Combined Action of Penicillin and the Sulfonamides in Vitro : The Nature of the Reaction

Abstract

The combined action of penicillin and the sulfonamides against bacteria has been demonstrated by several workers. Ungar (1943) reported that penicillin and sulfapyridine showed a marked additive effect both in vitro and in vivo against Staphylococcus aureus and hemolytic streptococci. Soo-Hoo and Schnitzer (1944) reported the additive effect of penicillin when combined with sulfanilamide or sulfapyridine against streptococci. Kirby (1944) using sulfadiazine and Bigger (1944) using sulfathiazole found that these compounds when combined with penicillin showed an additive effect against staphylococci and streptococci. T'ung (1944) found the in vitro sulfathiazole-penicillin combination more efficient than either compound alone when tested against several strains of Brucella. Hobby and Dawson (1944a) found a slight additive effect with sulfapyridine and none with sulfadiazine when these agents were combined with penicillin and tested against staphylococci and streptococci. They also reported that the rate of penicillin activity was reduced when small amounts of the sulfonamides were added. In the present paper we will report on the ability of three sulfonamides (sulfathiazole, sulfadiazine, and sulfapyrazine) to increase the activity of penicillin against ten sulfonamide-susceptible and sulfonamide-resistant strains of S. aureus and eight gram-negative rods. Observations indicating the mechanism of the in vitro additive effect are included in our experimental data. MATERIALS AND METHODS Media. Since extract and infusion broth markedly inhibited the action of the sulfonamides, a casein hydrolyzate medium (SMACO) was used, prepared according to the procedure of Strauss, Dingle, and Finland (1941). In preliminary titrations 20 per cent horse serum was added to the casein hydrolyzate medium, and, though this resulted in a slight reduction in titer, the results paralleled the data obtained with the unsupplemented casein hydrolyzate medium. The casein hydrolyzate medium, pH 7.2; was therefore used throughout the work. Chemotherapeutic agents. Crystalline penicillin,2 containing 1,667 units per mg, and commercial penicillin (Merck), containing 462 units per mg, were used. IThis investigation has been aided by a grant from the Josiah Macy, Jr., Foundation.

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

“…The relationship between synergism and drug resistance has been previously indicated by us in a report on the combined action of penicillin and the sulfonamides (Klein and Kalter, 1945). It was found that an important factor in the observed synergism was the ability of a small amount of an added drug, in this case the sulfonamide, to prevent the' multiplication of the few bacteria resistant to the test concentration of penicillin.…”

The Role of Spontaneous Variants in the Acquisition of Streptomycin Resistance by the Shigellae

“…We have previously shown that in the case of penicillin and the sulfonamides (Klein and Kalter, 1946) an important factor in the observed synergism resulted from the ability of a relatively low concentration of one chemotherapeutic agent to inhibit the small number of bacteria resistant to the other chemotherapeutic agent. In experiments which we will report at a later date we have found that bacteria resistant to streptomycin are still susceptible to penicillin and the sulfonamides, and that in vitro a combination of streptomycin with penicillin or sulfonamides, or both, was more effective than either agent alone.…”

The Role of Bacterial Resistance in Antibiotic Synergism and Antagonism

“…The ultimate justification for combined therapy then should be based on a combined effect that is greater than that achieved by the safe maxmum dosage of either drug alone. One rationale that appeared to justify combined therapy in infections due to a single agent was the inhibition of the development of drug resistance (Klein and Kalter, 1946; Klein and Kimmelman, 1947). The concept may be stated as follows: All bacterial populations show variation in the susceptibility of their individual cells to a given concentration of an antibiotic (Demerec, 1945; Klein, 1947).…”

“…Combinations of sulfonamides, penicillin, streptomycin, and p-aminosalicylic acid have been used quite extensively, and apparently the results have been considered satisfactory though controlled clinical studies on combined therapy are quite limited. One reservation concerning the use of combined drugs was pointed out in an earlier publication (Klein and Kalter, 1946; see also Chain and Duthie, 1945). It was shown that under certain conditions antagonism, as demonstrated by a significant inhibition of the bactericidal and lytic action of penicillin by an added sulfonamide, could be shown to occur in vitro.…”