MALDI‐TOF MS‐based drug susceptibility testing of pathogens: The example of Candida albicans and fluconazole

Abstract

MALDI‐TOF MS can be used for the identification of microorganism species. We have extended its application to a novel assay of Candida albicans susceptibility to fluconazole, based on monitoring modifications of the proteome of yeast cells grown in the presence of varying drug concentrations. The method was accurate, and reliable, and showed full agreement with the Clinical Laboratory Standards Institute's reference method. This proof‐of‐concept demonstration highlights the potential for this approach to test other pathogens.

Rapid Antifungal Susceptibility Testing by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Analysis

“…AFST continues to be a very dynamic field of medical mycology (41), since modifications of the available methods as well as other methodologies are increasingly being investigated (29,30,36). In this context, the recent appearance of biophysical methods, such as MALDI-TOF MS, in routine diagnostic microbiology laboratories holds the promise of significantly accelerating the detection of infections caused by fungal pathogens that are resistant to one or more antifungals (19,21). We have already witnessed the use of MALDI-TOF MS being expanded from fungal identification to antifungal susceptibility testing (19,(42)(43)(44).…”

“…Recently, we developed a MALDI-TOF MS-based assay for testing antifungal susceptibilities of clinically relevant Candida and Aspergillus species to the echinocandin caspofungin (CSF) (19) by means of a composite correlation index (CCI)-based approach (20). The method reliably and accurately allows a determination of the minimal profile change concentration (MPCC) (21), an endpoint value that is an alternative to the classical MIC, for CSF by relying on the proteome changes which are detectable after a 15-h exposure of fungal cells to serial drug concentrations (19). Endpoint readings by MALDI-TOF MS provide a clear time savings (15 h versus 24 h) over the CLSI-or EUCAST-based methods, but implementing MALDI-TOF MS into the daily workflow appears to offer only a subtle advantage to clinicians compared to that for recent strategies aimed at speeding up AFST (22,23).…”

Advances in Identification of Clinical Yeast Isolates by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…This concentration was termed the minimum profile change concentration (MPCC). A comparison of the MPCC to standard MIC based on broth microdilution revealed 94% agreement within a one doubling dilution range (49). Using the same methodology, De Carolis and colleagues evaluated the ability of MALDI-TOF MS to detect differences in protein profiles in C. albicans, C. glabrata, C. krusei, and C. parapsilosis in response to increasing concentrations of caspofungin.…”

Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry for Caspofungin Susceptibility Testing of Candida and Aspergillus Species

“…For MALDI-TOF MS-based caspofungin susceptibility assays, we adopted the protocol developed by Marinach et al (17), with some modifications. Briefly, aliquots of conidial inoculum sus-pensions of approximately 1 ϫ 10 6 cells per milliliter, as determined by a hemocytometric method (14), were added to RPMI, with serial dilutions (64 to 0.008 g/ml) of caspofungin (pure substance provided by Merck), or to RPMI alone as a negative control, into 24-well plates and kept at 37°C under agitation for 15 h. The cells then were washed twice with sterile water and resuspended in 10% formic acid.…”