Combined microassay and determination of bioactivity of N-acetylnystatin

The application of flow microcalorimetric bioassay for polyene antibiotics to nystatin and its N-acetyl derivative, and its extension to the measurement of their relative bioactivities are reported. The responding organism was Saccharomyces cerevisae. The bioactivity of the N-acetyl derivative is shown to be less than that of the parent antibiotic and to be concentration-dependent. A limited diffusion bioassay study supports these conclusions.