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Saccharomyces cerevisiae infections and antifungal susceptibility studies by colorimetric and broth macrodilution
R N Tiballi1, J E Spiegel, L T Zarins
1Department of Internal Medicine, Department of Veterans Affairs Medical Center, Ann Arbor, Michigan, USA.
Abstract:
Saccharomyces cerevisiae was isolated in large numbers from operative specimens from two patients with perforated bowel and peritonitis and from the blood of another patient treated with extracorporeal membrane oxygenation. Susceptibility studies were performed on these three isolates and another 29 isolates that colonized or caused infection in a total of 19 patients seen over the last decade. All isolates had low minimum inhibitory concentration (MIC) values for amphotericin B (MIC90 of < or = 0.02 microgram/ml) and flucytosine (MIC90 of 0.2 microgram/ml), and a broader range of MIC values for itraconazole (MIC90 of 0.8 microgram/ml) and fluconazole (MIC90 of 4 micrograms/ml). A colorimetric method using Alamar blue reagent showed good concordance with the standard broth macrodilution method for amphotericin B, flucytosine, and fluconazole, but less good concordance for itraconazole. Serious infections with S. cerevisiae probably should be treated with amphotericin B, with or without the addition of flucytosine.
Insights
Saccharomyces cerevisiae, a yeast, can cause serious infections. Antifungal susceptibility testing shows amphotericin B and flucytosine are effective treatments for Saccharomyces cerevisiae infections.
Area of Science:
- Medical Mycology
- Clinical Microbiology
Background:
- Saccharomyces cerevisiae is an opportunistic pathogen.
- Invasive infections caused by S. cerevisiae are rare but can be severe.
Observation:
- S. cerevisiae was isolated from patients with perforated bowel, peritonitis, and bloodstream infections.
- Antifungal susceptibility testing was performed on 32 isolates from 19 patients over a decade.
Findings:
- All isolates demonstrated low minimum inhibitory concentration (MIC) values for amphotericin B and flucytosine.
- MIC values for itraconazole and fluconazole were higher, indicating broader susceptibility ranges.
- The Alamar blue assay showed good concordance with standard methods for most antifungals, except itraconazole.
Implications:
- Amphotericin B is recommended as a primary treatment for serious S. cerevisiae infections.
- Flucytosine may be used as an adjunctive therapy.
- Further validation of rapid susceptibility testing methods is warranted.