The Relative Activity of Penicillins F, G, K, and X Against Spirochetes and Streptococci in Vitro

Abstract

Two lots of crystalline penicillin F, 3 lots of G, one of K, and 3 of X were assayed for strepto-coccidal activity (group A hemolytic streptococcus, C-203) and spirocheticidal activity (Spirocheta pallida, Reiter strain) in vitro. The relative activities per mg. of these crystalline prepns. against the streptococcus averaged 82, 100, 120, and 140 for F, G, K, and X, respectively, on one series of assays, and 70, 100, 110, and 130 in a 2d series. The corresponding activities against the spirochete were 53, 100, 76, and 51, respectively. In comparison, the relative activities of these four penicillins against Staphylococcus aureus are stated to be 90, 100, 138, and 54. Per (staphylococcidal) "unit", the activities of F, G, K, and X against the streptococcus averaged 85, 100, 85 and 250, and against the spirochete, 60, 100, 55, and 95. With each of the 3 organisms there was, therefore, approx. a 2 -fold difference between the least active and most active penicillin; but their relative activity varied un-predictably from organism to organism. The order of increasing activity was X < F < G < K for S. aureus, F < G < K < G for the spirochete. The therapeutic significance of these data is discussed in the text.