English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

SUMMARY: Streptomycin may be estimated in body fluids by allowing the fluid to diffuse through nutrient agar seeded with a culture of Staphylococcus wureus contained in small-diameter (3 . internal) glass tubes. The zone of inhibition produced is affected neither by the anaerobic conditions within the agar nor by the volume of the test fluid. Acidity of the test fluid invalidates the results, since the depth of the zone of inhibition is decreased. Increase in the size of the inoculum of the test organism also decreases the depth of the zone of inhibition. Small errors arisc from variations in timing during the setting-up of the test. The zones produced in the presence of different human sera differ slightly and to a degree similar to that found in the presence of various urines. The available mathematical expressions suggest that the square of the depth of the zone of inhibition is linearly related to the log of the concentration of an anti- biotic in the test fluid. Experimentally this relationship does not hold for low concentrations of streptomycin, probably due to the assumption of boundary con- ditions which cannot be defined with certainty ; but it is a better approximation than the assumption of a linear relationship between the depth of the zone of inhibition (unsquared) and the log of the streptomycin concentration. A method of statistical analysis is given in which a weighted regression line is fitted to the squared values of the zones of inhibition in a manner analogous to probit analysis. The routine method may be refined without undue labour to the point where assays are accurate to within + 5 yo. One of the most widely used methods for estimating streptomycin in body fluids is that of Stebbins & Robinson (1945). In this method the sensitivity to streptomycin of the test organism, a strain of Staphylococcus aureus, is increased by using 1 yo agar, slightly alkaline and with a low salt content. The solutions are applied to the surface of seeded plates in Oxford cylinders. A twofold increase in the concentration of streptomycin in the fluid to be assayed produces a smaller increase in the diameter of the zone of inhibition than is produced if similar solutions of penicillin are used. Variations caused by the method of applying the solution to the seeded agar therefore diminish the accuracy of the estimation to a greater extent. When using conventional plate methods with Oxford cylinders, filter-paper disks or cups cut with a cork borer, this source of variation decreases the accuracy of the estimation con- siderably. Variation is also increased by failing to use plates of uniform size with flat bottoms, which are difficult to obtain at the present time. It has been shown by Hayes (1945) that the depth of agar in the plates affects the size of the zone of inhibition when estimating the concentration of penicillin in fluids. To minimize these variations a method has been evolved in which the seeded agar is pipetted into lengths of 3 mm. internal diameter glass tubing

A Method of Estimating Streptomycin in Serum and Other Body Fluids by Diffusion through Agar Enclosed in Glass Tubes