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Journal of Clinical Microbiology, May 1998, p. 1197-1200, Vol. 36, No. 5
Clinical Microbiology Laboratory, York
Hospital, York, Pennsylvania 17405,1 and
Laboratories for Mycology, Axelrod Institute, Wadsworth Center,
New York State Department of Health, Albany, New York
12208-20022
Received 11 December 1997/Returned for modification 17 January
1998/Accepted 5 February 1998
The ability of the rapid, computerized Microbial Identification
System (MIS; Microbial ID, Inc.) to identify a variety of clinical
isolates of yeast species was compared to the abilities of a
combination of tests including the Yeast Biochemical Card (bioMerieux
Vitek), determination of microscopic morphology on cornmeal agar with
Tween 80, and when necessary, conventional biochemical tests and/or the
API 20C Aux system (bioMerieux Vitek) to identify the same yeast
isolates. The MIS chromatographically analyzes cellular fatty acids and
compares the results with the fatty acid profiles in its database.
Yeast isolates were subcultured onto Sabouraud dextrose agar and were
incubated at 28°C for 24 h. The resulting colonies were
saponified, methylated, extracted, and chromatographically analyzed (by
version 3.8 of the MIS YSTCLN database) according to the
manufacturer's instructions. Of 477 isolates of 23 species tested, 448 (94%) were given species names by the MIS and 29 (6%) were
unidentified (specified as "no match" by the MIS). Of the 448 isolates given names by the MIS, only 335 (75%) of the identifications
were correct to the species level. While the MIS correctly identified
only 102 (82%) of 124 isolates of Candida glabrata, the
predictive value of an MIS identification of unknown isolates as
C. glabrata was 100% (102 of 102) because no isolates of
other species were misidentified as C. glabrata. In
contrast, while the MIS correctly identified 100% (15 of 15) of the
isolates of Saccharomyces cerevisiae, the predictive value of an MIS identification of unknown isolates as S. cerevisiae was only 47% (15 of 32), because 17 isolates of
C. glabrata were misidentified as S. cerevisiae. The low predictive values for accuracy associated
with MIS identifications for most of the remaining yeast species
indicate that the procedure and/or database for the system need to be
improved.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Limitations of the Current Microbial Identification
System for Identification of Clinical Yeast Isolates
*
Corresponding author. Mailing address: Clinical
Microbiology Laboratory, York Hospital, 1001 S. George St., York,
PA 17405. Phone: (717) 851-2393. Fax: (717) 851-2707. E-mail:
jkellogg{at}yorkhospital.edu.
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