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Updated: Apr 18, 2026
Deferred Growth Inhibition Assay to Quantify the Effect of Bacteria-derived Antimicrobials on Competition
Published on: September 3, 2016
Determination of MICING: a new assay for assessing minimal inhibitory concentration for invasive growth
1Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000, Ljubljana, Slovenia, jure.zupan@fvz.upr.si.
Abstract:
Our work was focused on a new assay for characterising clinically important yeast. This assay was developed due to the need for new diagnostic methods for recognising potentially virulent strains of increasingly important non-albicans yeast pathogens, such as Saccharomyces cerevisiae and Candida glabrata. With the great diversity among strains for virulence and virulence factors, identification to the species level is not sufficient; therefore, testing for specific virulent traits remains the best option. We show here that the proposed assay uncovers the relationships between the three most important yeast virulence traits in a single test: the ability of a strain to invade solid medium, while resisting the presence of an antimycotic and high temperature (37 °C). We combined the quantitative agar invasion assay with classical antimycotic susceptibility testing into a single assay. Similarly to the minimal inhibitory concentration (MIC) value, we defined the MICING (minimal inhibitory concentration of antimycotic for invasive growth) as the concentration of an antimycotic above which the yeast invasive growth is significantly repressed. In this study, we tested three of the most common antimycotics: fluconazole, itraconazole and amphotericin B. The response of yeast strains invasion was characteristic of each antimycotic, indicating their mechanisms of action. In addition to MICING, the assay provides quantitative information about the superficial and invasive growth, and also about the relative invasion, which helps in identifying clinically important yeast, such as azole-resistant and/or invasive strains of S. cerevisiae and C. glabrata.
Insights
A new assay identifies virulent yeast strains by assessing their invasive growth, antimycotic resistance, and heat tolerance. This method aids in diagnosing challenging yeast infections caused by non-albicans species.
Area of Science:
- Medical Mycology
- Clinical Microbiology
- Diagnostic Assays
Background:
- Non-albicans yeasts like Saccharomyces cerevisiae and Candida glabrata are emerging pathogens.
- Species-level identification is insufficient for assessing yeast virulence.
- New diagnostic methods are needed to identify virulent yeast strains.
Purpose of the Study:
- To develop a novel assay for characterizing clinically important yeast virulence traits.
- To combine multiple virulence factor assessments into a single, efficient test.
- To improve the identification of potentially virulent and drug-resistant yeast strains.
Main Methods:
- Developed a quantitative agar invasion assay combined with antimycotic susceptibility testing.
- Defined MICING (minimal inhibitory concentration of antimycotic for invasive growth).
- Tested the assay using common antimycotics (fluconazole, itraconazole, amphotericin B) against yeast strains.
Main Results:
- The assay effectively assesses yeast invasive growth, antimycotic resistance, and heat tolerance (37°C).
- MICING values were determined for fluconazole, itraconazole, and amphotericin B.
- Yeast strain responses to antimycotics revealed characteristic invasion patterns and mechanisms of action.
Conclusions:
- The developed assay provides a comprehensive method for identifying clinically significant yeast.
- It aids in detecting azole-resistant and invasive strains of S. cerevisiae and C. glabrata.
- This assay enhances diagnostic capabilities for challenging yeast infections.
