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Antimicrobial susceptibility testing of six clinical isolates of Aspergillus
Abstract:
Several different methods of performing susceptibility tests on six clinical isolates of Aspergillus are described. Some of the conditions that affected the level of susceptibility to drugs were: the type of media used, temperature and time of incubation, and the initial inoculum size. For amphotericin B susceptibility testing, the effectiveness of the polyene antibiotic as measured by visual growth was equivalent to the effectiveness as measured by inhibition of ribonucleic acid synthesis and dry-weight increase. For 5-fluorocytosine and rifampin, the visual-turbidity method gave minimum inhibitory concentrations that were much higher than those determined by effects on ribonucleic acid synthesis and dry weight. The reason for these discrepancies in susceptibility testing with 5-fluorocytosine and rifampin are unknown. We conclude that the most relevant test of this fungus to antifungal agents will have to be determined by the correlation of in vitro data with animal experiments and clinical results.
Insights
Evaluating antifungal susceptibility testing for Aspergillus clinical isolates revealed method-dependent variations. Optimal testing requires correlating in vitro data with clinical outcomes for accurate antifungal efficacy assessment.
Area of Science:
- Mycology
- Clinical Microbiology
- Antifungal Drug Discovery
Background:
- Accurate antifungal susceptibility testing is crucial for treating invasive Aspergillus infections.
- Standardized methods are needed to ensure reliable in vitro susceptibility data.
Purpose of the Study:
- To evaluate different susceptibility testing methods for clinical Aspergillus isolates.
- To identify factors influencing antifungal susceptibility test results.
- To compare various endpoints for assessing antifungal drug effectiveness.
Main Methods:
- Testing six clinical Aspergillus isolates using multiple susceptibility assays.
- Varying parameters such as media type, incubation conditions, and inoculum size.
- Assessing drug effectiveness via visual growth, RNA synthesis inhibition, and dry-weight increase.
Main Results:
- Amphotericin B susceptibility showed consistent results across different measurement methods.
- 5-Fluorocytosine and rifampin minimum inhibitory concentrations varied significantly between visual turbidity and biochemical endpoints.
- Discrepancies for 5-fluorocytosine and rifampin suggest limitations in the visual turbidity method.
Conclusions:
- Susceptibility testing outcomes for Aspergillus are influenced by methodological factors.
- Visual turbidity may overestimate antifungal resistance for certain drugs like 5-fluorocytosine and rifampin.
- Correlation of in vitro data with animal models and clinical results is essential for relevant antifungal efficacy assessment.