Stable isotope labelling: an approach for MALDI-TOF MS-based rapid detection of fluconazole resistance in Candida...

With the rise of fluconazole resistance in Candida tropicalis in Asian countries, the rapid detection of resistance is required to optimize therapy.

We evaluated a stable isotope labelling by/with amino acids in cell culture (SILAC) approach for rapid detection of fluconazole resistance in C. tropicalis by MALDI-TOF MS.

Twenty-six fluconazole-resistant and 19 -susceptible C. tropicalis isolates were used. Isolates were grown in media containing normal lysine (NL), isotopically labelled ('heavy') lysine (HL) and fluconazole (FLC) with labelled lysine (HL + FLC). MALDI-TOF MS was performed, acquired spectra were visually compared and composite correlation index (CCI) values were calculated. The results were analysed by CCI matrix, virtual gel and principal component analysis (PCA).

The MICs of fluconazole in 26 resistant and 19 susceptible isolates were 16-256 mg/L and 0.5-1 mg/L, respectively. The m/z values of 15 peaks specific for media containing NL and their corresponding peaks specific for media with HL were detected to differentiate resistant and susceptible isolates. The CCI cut-off values for susceptible and resistant isolates were significant (P < 0.05). The CCI matrix, virtual gel and PCA dendrogram confirmed the results. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of this method for detection of fluconazole resistance were 92.31%, 100%, 100%, 90.48% and 95.56%, respectively.

SILAC, a promising approach for rapid resistance detection in C. tropicalis using MALDI-TOF MS, may be used in the routine laboratory in the near future.