A Turbidimetric Method for the Assay of Antibiotics

(1944). Standard methods for the assay of penicillin and streptomycin are used by the Food and Drug Administration (Federal Register, 1947, and recent re-visions) and by manufacturers of these antibiotics. Not one of these procedures is exactly applicable to the assay of antibiotic materials for which no standards have been established. EXPERIMENTAL DEVELOPMENT In order to develop a method that would be suitable for determining the antibiotic strength of experimental preparations, such as broth filtrates and chemical fractions as well as the finally purified substance, growth curves of many pathogenic bacteria were studied under varying conditions. Variables that were investigated include the amount of inoculum, the type of nutriment, and the presence or absence of antibacterial substances. The effect of varying the size of the inoculum is shown in figure 1. Figure 2 illustrates the differences between three different nutrients. The effect of the presence of small amounts of an antibacterial agent may be seen in figure 3.