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In vitro susceptibility testing in Aspergillus species: an update
1Department of Hygiene, Microbiology & Social Medicine, Division of Hygiene & Clinical Microbiology, Innsbruck Medical University, Fritz Pregl Str 3, 6020 Innsbruck, Austria. cornelia.lass-floerl@i-med.ac.at
Abstract:
Aspergillus species are the most common causes of invasive mold infections in immunocompromised patients. The introduction of new antifungal agents and recent reports of resistance emerging during treatment of Aspergillus infections have highlighted the need for in vitro susceptibility testing. Various testing procedures have been proposed, including macro- and micro-dilution, disk diffusion, Etest (AB Biodisk, Sweden) and other commercial tests. Although Aspergillus species are generally susceptible to various compounds, intrinsic and acquired resistance has been documented. Amphotericin B has limited activity against Aspergillus terreus and Aspergillus nidulans. Not surprisingly, continued use of azole-based drugs has the undesirable consequence of elevating the resistance of subsequent isolates from these patients. Several species in the Aspergillus fumigatus complex appear to be resistant to azoles; there is evidence of in vitro and in vivo correlation. Each in vitro susceptibility testing method has its own advantages and disadvantages. Etest is easy to perform and use on a daily basis, yet it is expensive. Disk diffusion is the most attractive alternative method to date, yet we lack sufficient data for aspergilli. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical Laboratory Standard Institute (CLSI) have produced reproducible reference testing methods. This article reviews the available methods for antifungal susceptibility testing in Aspergillus spp. as well as the scant data regarding the clinical implications of in vitro testing.
Insights
Antifungal resistance in Aspergillus infections necessitates reliable in vitro susceptibility testing. This review examines methods for testing Aspergillus susceptibility, crucial for guiding treatment in immunocompromised patients.
Area of Science:
- Medical Mycology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Aspergillus species are leading causes of invasive mold infections in immunocompromised individuals.
- Emerging antifungal resistance in Aspergillus necessitates robust in vitro susceptibility testing.
- Established and novel antifungal agents require careful monitoring for efficacy.
Purpose of the Study:
- To review current in vitro antifungal susceptibility testing methods for Aspergillus species.
- To discuss the advantages and disadvantages of various testing methodologies.
- To highlight the clinical implications of in vitro susceptibility data for Aspergillus infections.
Main Methods:
- Review of proposed and standardized in vitro susceptibility testing procedures.
- Comparison of methods including macro- and micro-dilution, disk diffusion, and Etest.
- Examination of data from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Clinical Laboratory Standard Institute (CLSI).
Main Results:
- Intrinsic resistance to Amphotericin B is noted in Aspergillus terreus and Aspergillus nidulans.
- Acquired azole resistance is increasing, particularly in the Aspergillus fumigatus complex, with in vitro-in vivo correlation.
- Various testing methods exist, each with unique benefits and drawbacks regarding cost, ease of use, and data availability.
Conclusions:
- Standardized reference methods from EUCAST and CLSI offer reproducibility for Aspergillus susceptibility testing.
- Further data is needed to fully establish the clinical utility of disk diffusion for Aspergillus.
- Accurate in vitro susceptibility testing is essential for optimizing antifungal therapy in patients with invasive aspergillosis.
