An agar diffusion assay method for the antifungal polyene, candidin

An agar diffusion cup assay method for candidin is described. Some conditions of the assay medium affecting growth rate of the test organism and diffusion rate of candidin are presented. Critical steps of the procedure were tested statistically for significant variation and found acceptable. Both the sodium salt and Zwitterionic forms of candidin can be assayed.

The rate of development of colonies of Bacterium lactis aerogenes on agar plates containing drugs

When bacteria are plated on a solid medium containing a drug, only a fraction α ∞ often very small, of the cells ever form colonies, α t , the fraction which have done so at time t , has been determined as a function of time, together with α ∞ , for various trained and untrained strains of bacteria in presence of a series of drugs. Bacterium lactis aerogenes (Aerobacter aerogenes) has been studied in this way in presence of brilliant green, proflavine, chloramphenicol, streptomycin, terramycin, thymol, sodium azide and iso nicotinyl hydrazine: and Bact . coli mutabile in presence of chloramphenicol, and propamidine. In some of the examples the curves of α t / α ∞ against time are clearly and obviously incompatible with the postulate that the resistant forms in the trained culture are pre-existent in the original. Separate experiments, moreover, have shown in these examples that a large concentration of non-resistant forms does not in fact delay the growth of forms already adapted . In other examples the α t / α ∞ against t curves are less sharply contrasted for the trained and untrained strains. Here, however, α ∞ for the trained strain may represent practically the whole population, while for the untrained strain it is 10 -6 or less. The statistical result of comparing, in attempts to estimate numbers of mutants, the average of one population with the extreme tail of another is examined. It is concluded that the α t / α ∞ relations, even in the second type of example, are as consistent with the occurrence of adaptations in competition with lethal action son the plate as they are with the growth of mutants. The resistance of strains re-tested after isolation from resistant colonies is highly variable.

IL GRANULOMA DA AGAR NELLO STUDIO DELLA REATTIVITA’ DEL MESENCHIMA DI ANIMALI TRATTATI CON METILCOLANTRENE E PORTATORI DI UN TUMORE TRAPIANTATO

Agar inserted into the subcutaneous tissue of rats gives rise to a granuloma with a peculiar structure. When methylcholanthrene is included in the agar the organization and the evolution of the granuloma are inhibited. Also when agar is inserted in the connective surrounding the Walker carcinoma or into the subcutaneous tissue of a tumour-bearing rat, quite an atypical granuloma is produced. It may be assumed that in such conditions the reaction properties of the connective tissue are modified.