Evaluation of MALDI-TOF MS for Identification of Species in the Candida parapsilosis Complex from Candidiasis Cases

Abstract

Background: Phenotypically identified Candida parapsilosis is actually a complex of 3 member species named Candida parapsilosis sensu stricto (CPSS), Candida orthopsilosis (CO), and Candida metapsilosis (CM), which can be identified only by molecular methods and automated methods such as MALDI-TOF mass spectrometry (MS). This study was undertaken to evaluate the VITEK MS, which uses the principle of MALDI-TOF MS for the identification of member species of C. parapsilosis complex (CPC).

Methods: In this cross-sectional study, 126 presumptively identified and stocked isolates of CPC were included. Definite identification to species level was done by VITEK MS and PCR as the gold standard method. Clinico-demographic characters and risk factors were analyzed. Antifungal susceptibility testing was performed for fluconazole and voriconazole.

Results: Twelve isolates were not identified as CPC either by VITEK MS or PCR and hence were excluded from the analysis. Out of 114 CPC isolates, 89 (78.1%), 18 (15.8%), and 7 (6.1%) isolates were identified as CPSS, CO, and CM, respectively, by VITEK MS. PCR identified 84 (79.2%), 15 (14.2%), and 7 (6.6%) isolates as CPSS, CO, and CM, respectively. However, PCR did not detect 8 isolates of CPSS detected by VITEK MS. VITEK MS showed 95.3% agreement in species identification and showed a kappa coefficient of 0.87, which is almost perfect agreement. Predominant isolations of all 3 species were from blood. Resistance was observed more in CPSS for both the azoles.

Conclusion: MALDI-TOF MS can be used as a rapid, reliable, cost-effective method to identify the species of CPC.

Keywords: Candida metapsilosis; Candida orthopsilosis; Candida parapsilosis sensu stricto; CM; CO; CPC; CPSS; MALDI-TOF MS; PCR.