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Journal of Clinical Microbiology, October 2000, p. 3696-3704, Vol. 38, No. 10
Institute of Medical Microbiology, University Hospital RWTH
Aachen, Aachen,1 and Robert
Koch-Institute, Berlin,2 Germany
Received 18 January 2000/Returned for modification 13 April
2000/Accepted 22 July 2000
Candida dubliniensis is often found in mixed culture
with C. albicans, but its recognition is hampered as the
color of its colonies in primary culture on CHROMagar Candida varies.
Furthermore, definite identification of C. dubliniensis is
difficult to achieve, time-consuming, and expensive. Therefore, a
method to discriminate between these two closely related yeast
species by fatty acid methyl ester (FAME) analysis using gas-liquid
chromatography (Sherlock Microbial Identification System [MIS]; MIDI,
Inc., Newark, Del.) was developed. Although the chromatograms of these
two species revealed no obvious differences when applying FAME
analysis, a new library (CADLIB) was successfully created using
Sherlock Library Generation Software (MIDI). The amount and
frequency of FAME was analyzed using library training files
(n = 10 for each species), preferentially those
comprising reference strains. For testing the performance of the
CADLIB, clinical isolates genetically assigned to the respective
species (C. albicans, n = 32; C. dubliniensis, n = 28) were chromatographically
analyzed. For each isolate tested, MIS computed a similarity index (SI)
indicating a hierarchy of possible strain fits. When using the newly
created library CADLIB, the SIs for C. albicans and
C. dubliniensis ranged from 0.11 to 0.96 and 0.53 to 0.93 (for all but one), respectively. Only three isolates of C. albicans (9.4%) were misidentified as C. dubliniensis, whereas all isolates of C. dubliniensis
were correctly identified. Resulting differentiation accuracy was
90.6% for C. albicans and 100% for C. dubliniensis. Cluster analysis and principal component analysis
of the resulting FAME profiles showed two clearly distinguishable clusters matching up with two assigned species for the strains tested. Thus, the created library proved to be well suited to discriminate between these two species.
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Differentiation between Candida dubliniensis and
Candida albicans by Fatty Acid Methyl Ester Analysis
Using Gas-Liquid Chromatography
*
Corresponding author. Mailing address: Institute of
Medical Microbiology, University Hospital RWTH Aachen, Pauwelsstr. 30, 52074 Aachen, Germany. Phone: 49 241 8089 515. Fax: 49 241 8888 483. E-mail: ghaase{at}post.klinikum.rwth-aachen.de.
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