J Clin Lab Anal. 2018;32:e22297. wileyonlinelibrary.com/journal/jcla
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© 2017 Wiley Periodicals, Inc.
Evaluation of direct antifungal susceptibility testing methods of
Candida spp. from positive blood culture bottles
Yasemin Oz | Egemen Gokbolat
Faculty of Medicine, Department of
Microbiology, Eskisehir Osmangazi University,
Yasemin Oz, Faculty of Medicine, Department
of Microbiology, Division of Mycology,
University of Eskisehir Osmangazi, Eskisehir,
Egemen Gokbolat, Department of
Microbiology, Burdur State Hospital, Burdur,
Eskisehir Osmangazi University Commission
Background: Blood culture is the gold standard diagnostic method in candidemia in
spite of long result time and low sensitivity rate. Early diagnosis is crucial for manage-
ment of candidemia because a delay in treatment is related with increased mortality.
We aimed to evaluate the direct applicability of antifungal susceptibility testing meth-
ods from positive blood culture bottles to save at least 24 hours.
Methods: Blood culture bottles were inoculated with 62 Candida isolates. Etest and
broth microdilution (BMD) methods for six antifungals, disk diffusion (DD) method for
two antifungals were performed, both directly from bottles and standardly.
Results: Essential agreements between direct and standard Etest methods were 87.1%
for caspofungin and >90% for other antifungals, but the agreements of them with
reference BMD were relatively low. Essential agreement between direct and standard
BMD was >93%. Correlation between direct and standard DD methods was very high,
negative correlations were observed between reference BMD and DD methods.
Conclusion: BMD is a reference method to evaluate the antifungal susceptibility, di-
rect application of BMD might provide reliable results at least 24 hours earlier. Direct
DD method may be a qualitative alternative. Direct susceptibility testing methods may
be very useful to initiating the appropriate treatment on time.
blood culture, broth microdilution, Candida, direct antifungal susceptibility, disk diffusion, Etest
1 | INTRODUCTION
Bloodstream infections (BSI) caused by Candida species are significant
causes of morbidity and mortality, especially in intensive care unit pa-
spp. were the fourth most common pathogens isolated from blood cul-
tures, the crude mortality rate of Candida infections was the highest
among all nosocomial BSI.
Therefore, rapid and accurate diagnostic
methods are essential for appropriate management of Candida BSIs.
However, blood culture is still the gold standard diagnostic method in
spite of long resulting time and low sensitivity rate in candidemia. The
standard method of blood culture involves at least overnight agar me-
dium subculture and then identification and antifungal susceptibility
testing after a bottle is signaled as positive for Candida; it is time con-
suming and can delay the appropriate therapy. Several standard meth-
ods were suggested for antifungal susceptibility testing of yeast by
M44-A2) and European Committee on Antimicrobial Susceptibility
Testing—EUCAST (E.DEF 7.2). Besides, there are many commercial
manual or automated systems such as Etest, Sensititre YeastOne, and
Vitek which are used commonly in many clinical laboratories.
Several studies including direct inoculation from positive blood
culture bottles have been performed in order to decrease the time
required for identification and/or antifungal susceptibility testing
In these studies, researchers reported promising results
by Etest, disk diffusion, flow cytometry, and some commercial systems
(Sensititre YeastOne and Vitek 2). Thus, antifungal susceptibility re-
sults could be obtained about 24 hours earlier than those obtained
with the standard procedure. Early start of proper antifungal treat-
ment can significantly improve the outcome of patients with candi-
demia because the mortality rate increases almost 1.5% for each hour
in delay of antifungal treatment.