Effects of amphotericin B in vitro on perfect and imperfect strains of Allescheria boydii.

The inhibitory effects of amphotericin B on Allescheria boydii vary with the strain studied. In general, most isolates of the fungus are not susceptible to concentrations within the range of human tolerance. This is particularly true of perfect forms, although this relationship is lacking for some isolates. There is no correlation between the isolation history of a strain and its amphotericin B sensitivity. Susceptibility was found to be absolute in some isolates, whereas resistance could be increased in others through repeated exposure to higher increments of drug. In high concentrations, the antibiotic is uniformly cidal for the spores of certain isolates. This finding was also true for some conidia of "resistant" strains, although the action was fungistatic on other spores in the same population.