Some principles of microbiological turbidimetric assays of antibiotics.

Turbidimetric methods for determining the potency of antibiotics are inherently more accurate and more precise than are comparable agar diffusion procedures, but assays conducted in liquid media are subject to degradation from less than ideal conditions to a much greater extent than are diffusion methods. The relationships between test organisms, antibiotics, and assay concentrations are discussed. A valid assay procedure must produce a linear response with an adequate slope (-0.

Effects of paper on performance of antibiotic-impregnated disks.

Grades of paper used in the manufacture and assay of antibiotic susceptibility disks have significant effects on the diffusion of antibiotics from the paper when compared to a control grade of paper. The papers also evoke different microbiological responses to changing concentrations of some antibiotics. Regulatory implications and the need for further standardization of assays among control laboratories are explored.