Bioassay method for polyene antibiotics based on the measurement of rubidium efflux from rubidium-loaded yeast cells

A bioassay method for the polyene antibiotics nystatin and amphotericin B is proposed based on the measurement of the efflux of rubidium ions from a rubidium-loaded yeast culture challenged with the antibiotics. For this purpose a major proportion of the intracellular K(+) ions in a Saccharomyces cerevisiae culture has been substituted by Rb(+) ions. The rubidium leakage is measured by atomic absorption spectrophotometry, and a straight-line, dose-response correlation has been obtained for both antibiotics.