[A new mathematical approach for determining antibiotic concentrations using the agar diffusion method].

A mathematical approach using the one-point intercept form of the equation of a straight line for the assay of antibiotic biological activity by the agar diffusion method is described. Insignificant alteration in the experimental conditions made it possible to markedly lower the volume of work and materials for the statistic processing. As distinct from the routine methods, the assay substance in three different concentrations is applied to three cavities on a dish and the standard substance in one control concentration is applied to the other three cavities on the same dish.

[Effect of Ca2+ ions on biosynthesis and component composition of tylosin in Streptomyces fradiae].

The influence of Ca2+ ions on biosynthesis of tylosin complex by Streptomyces fradiae in an enriched medium under submerged conditions was studied. It was shown that Ca2+ (at the concentration of 20 to 30 mM CaCl2) stimulated the tylosin biosynthesis by eliminating the limit of incorporation of the precursors such as macrocin and desmycosin to the process and by inhibiting catabolism of tylosin to relomycin. No potentiation of the Ca2+ influence by effectors of cAMP metabolism i.