Etest antifungals susceptibility testing directly from blood culture

Ref ID: 14170

Author: S. Costa de Oliveira1, A. P Silva1, F. Alves2, C. Correia2, A. G Rodrigues1, C. Pina-Vaz2

Author address:

1Porto Faculty of Medicine, PORTO, Portugal 2Hospital de São João, PORTO, Portugal

Full conference title:

4th Trends in Medical Mycology

Date: 18 October 2014

Abstract:

Objective: Fungaemia is associated with high mortality rate. Blood cultures have become one
of the most critically important tests in the clinical microbiology laboratory. Semi-automatic
systems are used to detect growth of microorganisms but subcultivation is mandatory for
identification or to perform susceptibility testing. This demands too much time for critically ill
patients Antifungal susceptibility profile is important but still is a cumbersome and lengthy
procedure. The purpose of this study was to evaluate Etest susceptibility to the main
antifungals directly from blood culture, as soon as growth is detected by BACTEC system.
Candida strains, with a known susceptibility profile, were inoculated on blood culture bottles
and Etest immediately performed after growth detection by the automatic system. The results
were compared with the reference method (CLSI, M27-A3).
Methods: An inoculum of 5 Candida cells/ml was suspended on Myco/F Lytic medium and
incubated in the Bactec 9000 system (Becton Dickinson, Sparks, Md). A total of 40 Candida
strains (14 C. albicans, 13 C. parapsilosis , 5 C. glabrata , 4 C. krusei and 4 C. tropicalis ) with
different antifungal phenotypes determined by microdilution method (CLSI, M27-A3 protocol)
were evaluated. Whenever the automatic system gave a positive result, aliquots was plated in
RPMI agar (BioMí©rieux, Paris) and MIC to six different antifungals (amphotericin B,
fluconazole, voriconazole, posaconazole, caspofungin and anidulafungin) was determined
using Etest (ABiodisk, Sweden). Minimal inhibitory concentration (MIC) was registered after 24
hours of incubation at 37ºC and the results compared with values obtained following the
microdilution method. Phenotypes were compared according to published CLSI breakpoints.
Results: Regarding amphotericin B no discrepant results were found for echinocandins, one
discrepant result for caspofungin and four for anidulafungin were found. Concerning azoles, a
larger number of discrepant results were found: for fluconazole in 19 cases (47.5%), for
voriconazole in 15 cases (37.5%) and for posaconazole in 12 cases (30%). The majority of the
errors were found with C. albicans . Etest was able to detect all resistant phenotypes; most
errors involved susceptible phenotypes that were reported as resistant.
Conclusion: Antifungal susceptibility testing with Etest directly from blood culture is a quick
and practical method to perform susceptibility testing although it overestimates the resistance
regarding azoles.
Acknowledgments: S Costa de Oliveira and A P Silva are supported by the grants
SFRH/BD/27662/2006 and SFRH/BD/29540/2006, respectively, from Portuguese Science and
Technology Foundation (FCT)

Abstract Number: P021

Conference Year: 2009

Link to conference website: NULL

New link: NULL


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