Maldi-Tof MS Analysis of Long-Term Stored Stock Candida Strains Identified by Molecular and Conventional Methods

Abstract

Objective: In recent years, the rapid and accurate identification of Candida isolates at species level has been of great importance for reasons such as increased incidence of infections due to Candida species and differing antifungal susceptibilities by species. Herein, we aimed to investigate the efficacy of the MALDI-TOF MS method in the identification of Candida clinical isolates stored at-20 degrees C for years.

Material and Method: Twenty eight Candida strains stored at-20 degrees C for more than 10 years without any recultivation and identified by various methods such as API (R) ID 32C, CHROMagar Candida and PCR-RFLP were included in the study. Isolates were subcultured and analysed by MALDI-TOF MS. An unidentified isolate at the species level previously and another isolate with low MALDI-TOF MS score were analyzed by ITS sequencing. Additionally, MALDI-TOF MS scores of 57 Candida strains isolated from routine cultures were compared with study isolates.

Results: Of them, 11 (39.3%) isolates were identified at the species level and 15 (53.6%) were identified at the genus level, while two isolates were outside the reliable identification limits by MALDI-TOF MS. MALDI-TOF MS yielded an accurate identification at the species level in all 28 isolates identified by various methods even though different scores were obtained.

Conclusion: MALDI-TOF MS is a cost effective, easy to use, fast and reliable method compared with the conventional and molecular methods for identification of stock Candida isolates preserved for many years. In conclusion, although a limited number of stock Candida isolates were included in the study, low identification scores for Candida isolates may be valuable in the MALDI-TOF MS analysis.