[In vitro testing of yeast resistance to antimycotic substances]

Investigations have been carried out in order to clarify the antibiotic susceptibility determination of yeasts. 291 yeast strains of different species were tested for sensitivity to 7 antimycotics: amphotericin B, flucytosin, nystatin, pimaricin, clotrimazol, econazol and miconazol. Additionally to the evaluation of inhibition zone diameters and MIC-values the influence of pH was examined. 1. The dependence of inhibition zone diameters upon pH-values varies due to the antimycotic tested. For standardizing purposes the pH 6.0 is proposed; moreover, further experimental parameters, such as nutrient composition, agar depth, cell density, incubation time and -temperature, have to be normed. 2. The relation between inhibition zone size and logarythmic MIC does not fit a linear regression analysis when all species are considered together. Therefore regression functions have to be calculated selecting the individual species. In case of the antimycotics amphotericin B, nystatin and pimaricin the low scattering of the MIC-values does not allow regression analysis. 3. A quantitative susceptibility determination of yeasts--particularly to the fungistatical substances with systemic applicability, flucytosin and miconazol, -- is advocated by the results of the MIC-tests.