Rapid identification and susceptibility testing of Candida spp. from positive blood cultures by combination of direct MALDI-TOF mass spectrometry and direct inoculation of Vitek 2

Fungaemia is associated with high mortality rates and early appropriate antifungal therapy is essential for patient management. However, classical diagnostic workflow takes up to several days due to the slow growth of yeasts. Therefore, an approach for direct species identification and direct antifu...

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Bibliographic Details
Published in:PloS one 2014-12, Vol.9 (12), p.e114834-e114834
Main Authors: Idelevich, Evgeny A, Grunewald, Camilla M, Wüllenweber, Jörg, Becker, Karsten
Format: Article
Language:English
Subjects:
Analysis
Antifungal agents
Antifungal Agents - pharmacology
Biology and Life Sciences
Blood
Blood - microbiology
Blood tests
Candida
Candida - drug effects
Candida - growth & development
Candida - isolation & purification
Candidiasis - diagnosis
Candidiasis - microbiology
Diagnostic systems
Dilution
Fluconazole
Fungicides
Health aspects
Humans
Inoculation
Mass spectrometry
Mass spectroscopy
Medicine and Health Sciences
Microbial Sensitivity Tests - methods
Minimum inhibitory concentration
Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods
Spectroscopy
Subculture
Voriconazole
Workflow
Yeast
Yeasts
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Summary:Fungaemia is associated with high mortality rates and early appropriate antifungal therapy is essential for patient management. However, classical diagnostic workflow takes up to several days due to the slow growth of yeasts. Therefore, an approach for direct species identification and direct antifungal susceptibility testing (AFST) without prior time-consuming sub-culturing of yeasts from positive blood cultures (BCs) is urgently needed. Yeast cell pellets prepared using Sepsityper kit were used for direct identification by MALDI-TOF mass spectrometry (MS) and for direct inoculation of Vitek 2 AST-YS07 card for AFST. For comparison, MALDI-TOF MS and Vitek 2 testing were performed from yeast subculture. A total of twenty four positive BCs including twelve C. glabrata, nine C. albicans, two C. dubliniensis and one C. krusei isolate were processed. Applying modified thresholds for species identification (score ≥ 1.5 with two identical consecutive propositions), 62.5% of BCs were identified by direct MALDI-TOF MS. AFST results were generated for 72.7% of BCs directly tested by Vitek 2 and for 100% of standardized suspensions from 24 h cultures. Thus, AFST comparison was possible for 70 isolate-antifungal combinations. Essential agreement (minimum inhibitory concentration difference ≤ 1 double dilution step) was 88.6%. Very major errors (VMEs) (false-susceptibility), major errors (false-resistance) and minor errors (false categorization involving intermediate result) amounted to 33.3% (of resistant isolates), 1.9% (of susceptible isolates) and 1.4% providing 90.0% categorical agreement. All VMEs were due to fluconazole or voriconazole. This direct method saved on average 23.5 h for identification and 15.1 h for AFST, compared to routine procedures. However, performance for azole susceptibility testing was suboptimal and testing from subculture remains indispensable to validate the direct finding.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0114834