Impact of different culture conditions on the identification of Candida krusei clinical isolates by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry system

Abstract

Abstract:

Objective To investigate the effects of different culture media, incubation time, culture temperature and gas environment on the identification of Candida krusei by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Methods Twenty-five strains of Candida krusei were collected from 17 hospitals of China Hospital Invasive Fungal Surveillance Net (CHIF-NET) program. Six culture media were tested, including Sabouraud dextrose agar supplemented with chloramphenicol (SDA-C), CHROMagar (CCP), trypticase soy agar supplemented with 5% sheep blood (BAP), chocolate agar supplemented with vancomycin (CAP-VA), China blue lactose rosolic acid agar (CBA/R) and MacConkey agar (MAC). All isolates were identified by sequencing of the rDNA internal transcribed spacer (ITS) region as "gold standard". Isolates were incubated at 28℃ and 35℃ for 24 or 48 hours, with/without 5% CO₂ gas, and then identification was carried out by two MALDI-TOF MS systems. Results All (175/175) isolates incubated for 24 hours and 48 hours were identified correctly by Vitek MS. In comparison, Bruker Biotyper correctly identified 98.86% (173/175) isolates incubated for 24 hours and 87.43% (153/175) isolates incubated for 48 hours. All strains inoculated on SDA-C medium were correctly identified by both MALDI-TOF MS systems, but the accuracy of the species level of identification of which grown on SDA-C at 28℃ is higher than those grown at 35℃. With 48 hours' incubation, the correct identification rates by Bruker Biotyper were higher for strains grown on SDA than other media. Conclusion The correct identification rate of 24-hour incubated strains was higher than the rate of 48-hour incubated strains by Bruker MS. Compared with cultured at 35℃, the identification of Candida krusei strains grown at 28℃ was more accurate. SDA-C was the most suitable media for MALDI-TOF MS identification in our study. The results were reliable for Bruker Biotyper MALDI-TOF MS system with score values of≥1.700.

Key words: Candida krusei, identification, culture conditions, MALDI-TOF MS

CLC Number:

R379.4

HUANG Jing-jing, FAN Xin, XIAO Meng, XU Zhi-peng, ZHANG Ge, XU Ying-chun. Impact of different culture conditions on the identification of Candida krusei clinical isolates by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry system[J]. Chinese Journal of Mycology, 2020, 15(5): 262-267.

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