A rapid micromethod for bioautographic assay.

The detection and identification of specific molecules may often be accomplished most conveniently by autographic methods. These procedures, in which nutritionally deficient bacterial cells suspended in solid minimal media show zones of growth in the presence of the required nutrilite, possess several advantages over liquid assay methods. These Include simplicity of technique and the reduction of interference from inhibitory materials which may be present in crude samples as natural constituents or as residues from extraction procedures (Usdin et al., 1954), as well as direct applicability to paper chromatograms for the identification of spots (Winsten and Eigen, 1948). Their principal disadvantage, that samples of relatively high concentration are required, has been compensated for by the incorporation of tetrazolium salts in the solid medium. Reduction of these compounds to colored derivatives during growth of the test bacteria gives a criterion of response whose sensitivity to absolute amounts of growth factors is better than with tube assay (Ford and Holdsworth, 1953; Usdin et al., 1954). The method presented here offers a further increase in sensitivity and in economy of time and materials which may extend the usefulness of autography.