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Kim, Shin, Kee, Kim, Shin, Suh, and Ryang: Evaluation of VITEK-2 Antifungal Susceptibility Test (AST-YS01) for Candida Species Isolates in Korea
Original Article

Korean J Clin Microbiol 2009;12(3):122-128.

Published online: 22 September 2009

DOI: https://doi.org/10.5145/KJCM.2009.12.3.122

Evaluation of VITEK-2 Antifungal Susceptibility Test (AST-YS01) for Candida Species Isolates in Korea

Da-Woon Kim, Jong Hee Shin, Seung Jung Kee, Soo-Hyun Kim, Myung Geun Shin, Soon Pal Suh, Dong Wook Ryang

Department of Laboratory Medicine, Chonnam National University Medical School, Gwangju, Korea

Correspondence: Jong Hee Shin, Department of Laboratory Medicine, Chonnam National University Medical School, 671, Jebong-ro, Dong-gu, Gwangju 501-757, Korea. (Tel) 82-62-220-5342, (Fax) 82-62-224-2518, (E-mail) shinjh@chonnam.ac.kr

Received 20 April 20095 June 2009       Accepted 15 July 2009

Copyright © 2009 Korean Journal of Clinical Microbiology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

VITEK-2 yeast susceptibility test (AST-YS01; bioMerieux, Hazelwood, MO, USA) has recently been introduced as a fully automated commercial antifungal susceptibility test system that determines MIC (minimum inhibitory concentrations) endpoints spectrophotometrically, thereby eliminating subjective errors. We compared the VITEK-2 system with the CLSI (the Clinical and Laboratory Standards Institute) M27 method for susceptibility testing of Candida isolates from Korea.

Methods

A total of 175 Candida bloodstream isolates were collected from two hospitals during a 18-month period. We compared the MIC results for amphotericin B, fluconazole and voriconazole obtained with the VITEK-2 system to those obtained by the CLSI M27 broth microdilution method after 24-hr and 48-hr incubation.

Results

VITEK-2 system MIC endpoints for 175 isolates were determined after 11.75 to 35.50 hr of incubation (mean, 16.3±4.8 hr). The essential agreement (within 2 dilutions) between amphotericin B, fluconazole and voriconazole MICs obtained by the VITEK-2 system and CLSI method was 98.3%, 90.9% and 96.0%, respectively, at 24-hr incubation and 100%, 92.6% and 94.9%, at 48-hr incubation. The categorical discrepancy for fluconazole was 6.3% (major error, 2.9% and minor error, 3.4%) at 24-hr and 6.3% (major error, 2.3% and minor error, 4.0%) at 48-hr. The categorical discrepancy for voriconazole was 1.7% (major error, 1.1% and minor error, 0.6%) at both 24-hr and 48-hr. There were no very major errors for fluconazole and voriconazole.

Conclusion

The VITEK-2 antifungal susceptibility test system appears to be rapid and highly correlative with the CLSI method, sugesting that this system can be effective for antifungal susceptibility testing for Candida species in the clinical laboratory.

Keywords: Candida, VITEK-2, Antifungal susceptibility, CLSI

REFERENCES

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Table 1.
In vitro susceptibilities of 175 isolates of Candida spp. to amphotericin B, fluconazole and voriconazole as determined with the VITEK-2 system and by CLSI BMD methods
Species (no. of isolates tested) Antifungal agent Test method∗ MIC (ug/mL) EA (%)†
Range 50% 90%
C. albicans (64) Amphotericin B VITEK-2 ≤0.25-1 0.5 1  
Amphotericin B CLSI-24 0.125-1 0.25 0.5 100.0
Amphotericin B CLSI-48 0.125-1 0.5 0.5 100.0
Fluconazole VITEK-2 ≤1-≥64   8  
Fluconazole CLSI-24 0.125-0.5 0.125 0.25 85.9
Fluconazole CLSI-48 0.125-0.5 0.125 0.25 85.9
Voriconazole VITEK-2 ≤0.12-1 ≤0.12 ≤0.125  
Voriconazole CLSI-24 ≤0.03 ≤0.03 ≤0.03 95.3
Voriconazole CLSI-48 ≤0.03 ≤0.03 ≤0.03 95.3
C. parapsilosis (50) Amphotericin B VITEK-2 ≤0.25-4 0.5 1  
Amphotericin B CLSI-24 0.1255-0.5 0.25 0.5 94.0
Amphotericin B CLSI-48 0.25-1 0.5 1 100.0
Fluconazole VITEK-2 ≤1-≥64 ≤1 ≤1  
Fluconazole CLSI-24 0.125-2 0.5 1 98.0
Fluconazole CLSI-48 0.25-4 0.5 2 98.0
Voriconazole VITEK-2 ≤0.125 ≤0.125 ≤0.125  
Voriconazole CLSI-24 ≤0.03 ≤0.03 ≤0.03 100.0
Voriconazole CLSI-48 ≤0.03-0.25 ≤0.03 0.06 100.0
C. tropicalis (32) Amphotericin B VITEK-2 ≤0.25-1 0.5 0.5  
Amphotericin B CLSI-24 0.25-0.5 0.5 0.5 100.0
Amphotericin B CLSI-48 0.5-1 0.5 0.5 100.0
Fluconazole VITEK-2 ≤1-≥64 ≤1 2  
Fluconazole CLSI-24 0.125-1 0.25 0.5 93.8
Fluconazole CLSI-48 0.125-4 0.5 1 93.8
Voriconazole VITEK-2 ≤0.125-≥8 ≤0.125 ≤0.125  
Voriconazole CLSI-24 ≤0.03 ≤0.03 ≤0.03 93.8
Voriconazole CLSI-48 ≤0.03-0.25 0.06 0.125 93.8
C. glabrata (10) Amphotericin B VITEK-2 ≤0.25-1 0.5 1  
Amphotericin B CLSI-24 0.125-0.5 0.5 0.5 100.0
Amphotericin B CLSI-48 0.125-1 0.5 0.5 100.0
Fluconazole VITEK-2 2-≥64 8 16  
Fluconazole CLSI-24 2- 64 4 8 80.0
Fluconazole CLSI-48 4-≥64 16 16 90.0
Voriconazole VITEK-2 ≤0.125-≥8 ≤0.125 2  
Voriconazole CLSI-24 0.06-2 0.125 0.25 80.0
Voriconazole CLSI-48 0.125-2 0.5 1 60.0
C. guilliermondii (6) Amphotericin B VITEK-2 ≤0.25-0.5 ≤0.25    
Amphotericin B CLSI-24 0.125-0.25 0.25   100.0
Amphotericin B CLSI-48 0.25-0.5 0.25   100.0
Fluconazole VITEK-2 2-≥64 2    
Fluconazole CLSI-24 1-8 2   83.3
Fluconazole CLSI-48 2-32 4   100.0
Voriconazole VITEK-2 ≤0.125-0.5 ≤0.125    
Voriconazole CLSI-24 ≤0.03-0.06 ≤0.03   100.0
Voriconazole CLSI-48 0.06-0.25 0.125   100.0
Other (13) Amphotericin B VITEK-2 ≤0.25-1 ≤0.25 1  
Amphotericin B CLSI-24 0.125-0.5 0.25 0.5 100.0
Amphotericin B CLSI-48 0.25-1 0.5 1 100.0
Fluconazole VITEK-2 ≤1-8 2 4  
Fluconazole CLSI-24 0.125-4 0.5 2 92.3
Fluconazole CLSI-48 0.125-8 1 4 100.0
Voriconazole VITEK-2 ≤0.125-0.25 ≤0.125 0.25  
Voriconazole CLSI-24 ≤0.03-0.125 ≤0.03 0.125 100.0
Voriconazole CLSI-48 ≤0.03-0.125 ≤0.03 0.125 100.0
All Candida spp. (175) Amphotericin B VITEK-2 ≤0.25-4 0.5 1  
Amphotericin B CLSI-24 0.125-1 0.25 0.5 98.3
Amphotericin B CLSI-48 0.125-1 0.5 1 100.0
Fluconazole VITEK-2 ≤1-≥64 1 8  
Fluconazole CLSI-24 0.125-64 0.25 2 90.9
Fluconazole CLSI-48 0.125-≥64 0.5 4 92.6
Voriconazole VITEK-2 ≤0.125-≥8 ≤0.125 ≤0.125  
Voriconazole CLSI-24 ≤0.03-2 ≤0.03 ≤0.03 96.0
  Voriconazole CLSI-48 ≤0.03-2 ≤0.03 0.125 94.9

∗ CLSI-24 and CLSI-48, CLSI incubation for 24 hr and 48 hr, respectively; †EA (Essential agreement, ±2log2 dilutions) between VITEK-2 and CLSI MICs.

Table 2.
Categorical agreement between the fluconazole and voriconazole MICs determined by VITEK-2 system and CLSI 24-hr and 48-hr BMD method for 175 isolates of Candida spp.
Species (no. of isolates tested) Antifungal agent Test method % of MICs by catergry CA (%) % Errors
S SDD R VME ME Minor
C. albicans (64) Fluconazole VITEK-2∗ 95.3 1.6 3.1        
Fluconazole CLSI-24 100.0 0.0 0.0 95.3 0.0 3.1 1.6
Fluconazole CLSI-48 100.0 0.0 0.0 95.3 0.0 3.1 1.6
Voriconazole VITEK-2 100.0 0.0 0.0        
Voriconazole CLSI-24 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Voriconazole CLSI-48 100.0 0.0 0.0 100.0 0.0 0.0 0.0
C. parapsilosis (50) Fluconazole VITEK-2 98.0 0.0 2.0        
Fluconazole CLSI-24 100.0 0.0 0.0 98.0 0.0 2.0 0.0
Fluconazole CLSI-48 100.0 0.0 0.0 98.0 0.0 2.0 0.0
Voriconazole VITEK-2 100.0 0.0 0.0        
Voriconazole CLSI-24 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Voriconazole CLSI-48 100.0 0.0 0.0 100.0 0.0 0.0 0.0
C. tropicalis (32) Fluconazole VITEK-2 93.8 3.1 3.1        
Fluconazole CLSI-24 100.0 0.0 0.0 93.8 0.0 3.1 3.1
Fluconazole CLSI-48 100.0 0.0 0.0 93.8 0.0 3.1 3.1
Voriconazole VITEK-2 96.9 0.0 3.1        
Voriconazole CLSI-24 100.0 0.0 0.0 96.9 0.0 3.1 0.0
Voriconazole CLSI-48 100.0 0.0 0.0 96.9 0.0 3.1 0.0
C. glabrata (10) Fluconazole VITEK-2 60.0 40.0 0.0        
Fluconazole CLSI-24 100.0 0.0 0.0 60.0 0.0 0.0 40.0
Fluconazole CLSI-48 40.0 60.0 0.0 60.0 0.0 0.0 40.0
Voriconazole VITEK-2 80.0 10.0 10.0        
Voriconazole CLSI-24 100.0 0.0 0.0 80.0 0.0 10.0 10.0
Voriconazole CLSI-48 100.0 0.0 0.0 80.0 0.0 10.0 10.0
C. guilliermondii (6) Fluconazole VITEK-2 83.3 0.0 16.7        
Fluconazole CLSI-24 100.0 0.0 0.0 83.3 0.0 16.7 0.0
Fluconazole CLSI-48 83.3 16.7 0.0 83.3 0.0 0.0 16.7
Voriconazole VITEK-2 100.0 0.0 0.0        
Voriconazole CLSI-24 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Voriconazole CLSI-48 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Other (13) Fluconazole VITEK-2 100.0 0.0 0.0        
Fluconazole CLSI-24 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Fluconazole CLSI-48 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Voriconazole VITEK-2 100.0 0.0 0.0        
Voriconazole CLSI-24 100.0 0.0 0.0 100.0 0.0 0.0 0.0
Voriconazole CLSI-48 100.0 0.0 0.0 100.0 0.0 0.0 0.0
All Candida spp. (175) Fluconazole VITEK-2 93.7 3.4 2.9        
Fluconazole CLSI-24 100.0 0.0 0.0 93.7 0.0 2.9 3.4
Fluconazole CLSI-48 96.0 4.0 0.0 93.7 0.0 2.3 4.0
Voriconazole VITEK-2 98.3 0.6 1.1        
Voriconazole CLSI-24 100.0 0.0 0.0 98.3 0.0 1.1 0.6
  Voriconazole CLSI-48 100.0 0.0 0.0 98.3 0.0 1.1 0.6

∗ Initial VITEK-2 data.

Abbreviations: S, susceptible; SDD, susceptible dose dependent; R, resistant; CA, categorical agreement; VME, very major error; ME, major error; Minor, minor error; CLSI-24 and CLSI-48, CLSI method read at 24 hr and 48 hr of incubation, respectively.

Table 3.
Testing results for 14 Candida isolates showing a categorical disagreement of antifungal MIC results between VITEK-2 AST-YS01 and CLSI BMD method
Testing antifungals Isolate No. Species CLSI Initial VITEK test Repeat VITEK test
MIC at 24-hr MIC at 48-hr MIC (ug/mL) Category Incubation (h) MIC (ug/mL) Category Incubation (h)
Fluconazole 1 C. albicans 0.125 S 0.125 S ≥64 R 13.75 ≤1 S 14.0
2 C. albicans 0.25 S 0.25 S ≥64 R 15.0 ≤1 S 12.75
3 C. parapsilosis 0.5 S 1 S ≥64 R 35.25 ≤1 S 18.0
4 C. tropicalis 0.25 S 1 S ≥64 R 24.75 ≤1 S 12.75
5 C. guilliermondii 8 S 32 SDD ≥64 R 22.0 2 S 18.0
6 C. albicans 0.125 S 0.25 S 16 SDD 13.25 4 S 12.75
7 C. tropicalis 0.25 S 0.5 S 16 SDD 13.25 ≤1 S 12.5
8 C. glabrata 4 S 16 SDD 2 S 15.25 4 S 15.25
9 C. glabrata 4 S 16 SDD 4 S 17.25 4 S 14.0
10 C. glabrata 8 S 16 SDD 8 S 16.0 16 SDD 16.25
11 C. glabrata 4 S 16 SDD 32 SDD 14.5 8 S 14.0
12 C. glabrata 4 S 16 SDD 16 SDD 34.5 32 SDD 20.50
13 C. glabrata 8 S 32 SDD 32 SDD 35.5 16 SDD 17.25
  14 C. glabrata 2 S 8 S 16 SDD 28.0 2 S 15.0
Voriconazole 4 C. tropicalis ¿0.125 S 0.06 S   R 24.75 ≤0.125 S 12.75
13 C. glabrata ¿0.125 S 1 S   R 35.5 1 S 17.25
  14 C. glabrata 0.25 S 0.25 S 2 SDD 28.0 ≤0.125 S 15.0
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