A Rapid Microbiological Assay for Nystatin Using Rt⁺ Enriched Yeast Cells

Abstract

A simple, rapid (30 min) microbiological assay for nystatin is discussed. It is based on the efflux of Rb+ ions from nystatin treated yeast cells which had been grown in a medium enriched with this element. Results obtained with this method and the conventional agar diffusion method for nystatin in raw materials and finished products compare favourably both in accuracy and reproducibility. For simplicity and reproducibility, a cryogenically‐stored inoculum is advocated; its use gives a confidence interval (P= 0·05) on six results of < 5%.

A Rapid Bioassay Method for Gramicidin by Measuring Rubidium Ion Leakage from Streptococcus faecalis

“…More recently Clements-Jewery (1976) and Cosgrove (1978) have shown good nystatin-mediated release of cations from the yeast Saccharomyces cerevisiae after incubation times of 60 and 30 rnin respectively. The 30 min incubation time used in this study was sufficient to allow good release of Rb+ from the cells and also permitted the assay to be completed rapidly.…”

“…Rb+ cations may be detected by various means including atomic absorption spectrophotometry (Cosgrove 1978) and by using the radioactive isotope 86Rb (Harold & Baarda 1967). Drazin & Lehrer (1976), however, considered this latter method to have two main disadvantages, these being the high cost and relatively short half-life of the isotope.…”

The application of cryobiology to the microbiological assay of nystatin

“…The reproducibility accessible through the use of liquid nitrogen stored inocula in combination with standard stock solutions permits consideration of a reduction in the number of replicates required t o give a defined overall reproducibility in the assay and also brings the assay t o within the same levels of precision obtained using other methodological forms of assay, e.g. microcalorimetry (Beezer et a1 1977 a,b), atomic absorption spectrophotometry (Cosgrove 1978).…”

“…Improvements in reproducibility in microbiological assays have been claimed for the use of cryogenically (under liquid nitrogen) stored inocula. These include Sarcina lutea for antibiotic assays (Stapert et a1 1964), Saccharomyces carlsbergensis for vitamin assay (Tsuji 1966 a,b), Saccharomyces cerevisiae for polyene antibiotic assays by microcalorimetry (Beezer et al 1977 a,b), and by cell component leakage (Cosgrove 1978), and Streptococcus faecalis for the assay of chlorhydroxyquinoline (Cosgrove 1977). Only for the determination of this drug and for the polyene antibiotic assays has sufficient analytical detail been given to illustrate the quantitative improvements in reproducibility achieved by the use of such inocula.…”