Estimation of the Anti-Bacterial Activity of Fungi that are Difficult to Grow on Liquid Media

Abstract

THE more detailed work on the quantitative estimation of bacteriostatic substances has been concerned with the assay of penicillin, and the most generally favoured method is the 'cylinder' method as given by Abraham et al.¹, amplified by Heatley² and discussed by Foster and Woodruff³. On beginning our investigation in 1941, the above method was tried but, though apparently satisfactory for its original specific purpose, we found it to be less so for the widespread estimation of the bacteriostatic effect of fungus extracts and metabolism solutions than a method devised by ourselves⁴. Briefly, this method consists of putting a few drops of the liquid to be tested into a circular hole cut in the centre of a plate of bulk-seeded agar medium, with the subsequent production, after incubation at 37° C., of a zone of bacterial inhibition the width of which varies in proportion to the concentration of the bacteriostatic substance. This method only differs from somewhat similar methods mentioned by other workers in that the standardized technique enables it to give a relatively quantitative estimation.