Cytochemical Mechanisms of Penicillin Action

Abstract

Trace amts. of Co in broth markedly lower the concn. of penicillin required to inhibit Staphylococcus aureus. Concomitant tests with suitable rH and pH indicators confirm the "endpoint" concns. that were detd. on the basis of turbidity. In the controls and in the Co series exposed to penicillin the same morphological and cytochemical changes occurred, viz., a tendency to change from the normal colonial habit of growth to the formation of "streptococcus like" chains of swollen cells which may become arranged in plates and finely separate to form "diplococ-cus like" structures that evidence bipolar staining with vital dyes instead of the normal tendency to accumulate such dyes in the central vacuolar material. Similar phenomena were demonstrated on assay plates exposed to penicillin. Observations of turbidity, of response of the cultures to rH and pH indicators, and morphological changes in the cells, indicate the existence of an optimum concn. of penicillin above and below which inhibition of cellular activity is less pronounced. Similar evidence of an optimum concn. was obtained in tests of the 9-a.mino-acridine salt of penicillin tested against Bacillus subtilis. An approximation is made of the concn. of penicillin at the site of the periphery of inhibition zones on assay plates seeded with S. aureus.