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Comparison of antifungal susceptibility test methods for yeasts using broth microdilution, EtestTM and Fungitest

Abstract number: 1734_181

Perovic O., Rosmarin C., Wadula J., Gould S., McCarthy K., Orton D., Antelme D., Bhagoobhai L., Duse A.

Introduction: Antifungal drug resistance is likely to be a result of the increased use of antifungal agents as treatment and prophylaxis and is associated with high morbidity and mortality. Appropriate initial therapy for invasive fungal infections may require the introduction of susceptibility testing for selected isolates. Reference guidelines are based on a broth microdilution method. Agar dilution, EtestTM, disk testing, and modified broth microdilution technique, have been deemed to be easier to perform, time efficient and less laborious. An evaluation of three test methods was proposed in our hospitals to select for the most optimal test.

Objectives of our study were to determine the susceptibility of mucosal and invasive isolates of Candida species using the broth microdilution technique and to compare the EtestTM and Fungitest® test methods to the reference method.

Methods: Test evaluations were performed at the Johannesburg, Chris Hani Baragwanath hospitals and Mycology Reference Unit during 2006.

Eighty eight invasive clinical isolates of Candida species including albicans, glabrata, parapsilosis, tropicalis, krusei, dublinsiensis, guillermondii, were analysed.

The CLSI broth microdilution method M27-A2, EtestTM and Fungitest were performed.

Antifungal susceptibility profiles were compared amongst fluconazole, and amphotericin B. All assays were carried simultaneously and results read at 24 h as well as 48 h of incubation. The tests were performed according to manufacturer instruction.

Results: MIC 90 and 50 for amphotericin B and fluconazole for all our isolates are presented in the Table. For amphotericin B all three test methods had a high concordance. For fluconazole there was poor agreement between Fungitest® and broth microdilution test and a high number of major errors were identified.

Susceptibility of Candida spp. to antifungal agents determined by CLSI M27-A2 broth dilution MIC reference method

SpeciesNo. testedAntifungal agentMIC (mg/mL)
MIC50MIC90  
Candida albicans46Amphotericin B0.1250.25
Fluconazole28   
Candida dubliniensis1Amphotericin B0.1250.25
Fluconazole3264   
Candida glabrata13Amphotericin B0.2532
Fluconazole0.564   
Candida guilliermondii1Amphotericin B0.51
Fluconazole3264   
Candida krusei9Amphotericin B0.250.5
Fluconazole3264   
Candida parapsilosis5Amphotericin B0.250.5
Fluconazole816   
Candida tropicalis4Amphotericin B0.250.5
Fluconazole1632   

The best agreement was observed with the EtestTM 48hours for Candida species where correlation was 88% at 48 h compare to 58.7% at 24 hours. Fungitest® showed 6.25% and 46.87% at 24 h and 48 h respectively.

Conclusion: We founded that the EtestTM for fluconazole performed better in predicting resistance than the Fungitest®. Also, results of EtestTM at 24 hours were equivalent to 48 hour readings, thus allowing for a more rapid result, a feature not found for the Fungitest®. Therefore the EtestTM would be more suitable and efficient in a routine academic microbiology laboratory.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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