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Published on: May 28, 2014
Evaluation of a Liquid Media MALDI-TOF MS Protocol for the Identification of Dermatophytes Isolated from Tinea
Pauline Lecerf1, Roelke De Paepe2, Yasaman Jazaeri1
1Dermatology Department, University Hospital Brugmann & Saint-Pierre, Université Libre de Bruxelles, 1020 Brussels, Belgium.
Abstract:
One of the most common types of tinea is the superficial infection of the hair and scalp area known as tinea capitis. It is responsible for frequent outbreaks in nurseries and schools and represents a global health problem. Correct identification of the infection agent is essential in the determination of the infection source, epidemiological course, and treatment initiation. The conventional identification methods (direct exam, culture, DNA sequencing) are time-consuming, require experienced staff, are time-consuming, and the latter is expensive for routine identifications. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is gaining new ground for routine identification of filamentous fungi. The main advantages of MALDI-TOF MS are its rapid and accurate identification capability, relatively low cost, and easy integration into the laboratory routine. Its accuracy heavily depends on the quality of the reference spectra database. Identification of clinical isolates with MALDI-TOF MS protocol requires a sub-culturing step to ensure reliable identification. It can take days to weeks before fungal growth appears on solid medium. In this study, a unique MALDI-TOF MS protocol using liquid cultures of dermatophyte species was developed in order to shorten the turnaround time for the culture and identification of clinical isolates. Material and Method A standard MALDI-TOF MS protocol was adapted for liquid instead of solid cultures. Three different databases were tested. Results Using the liquid media MALDI-TOF MS protocol, a global rate of 62% correct identification (RCI) was obtained, compared with 87% for the protocol based on solid cultures. Trichophyton tonsurans was not correctly identified in all isolates using liquid cultures, with 88% of the isolates misidentified as Trichophyton interdigitale. The turnaround time for primary isolates for the solid and liquid protocols were respectively 11.7 and 11.6 days (no significant difference between both methods (p = 0.96)). Conclusions The newly designed liquid MALDI-TOF MS protocol did not lead to a significantly shorter turnaround time for the identification of dermatophytes isolated from tinea capitis infections. The turnaround time for the method with primary isolates was not significantly lower, and the rate of correct identification decreased remarkably, which emphasizes the need for a sub-culturing step. Using different database did not lead to improvement in turnaround time or rate of correct identification. This study highlights the importance of the medium and the reference database when performing MALDI-TOF MS.
Insights
Developing a liquid culture method for Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) did not speed up tinea capitis diagnosis. This approach reduced identification accuracy, highlighting the need for sub-culturing and robust reference databases.
Area of Science:
- Mycology
- Clinical Diagnostics
- Mass Spectrometry
Background:
- Tinea capitis, a common superficial fungal infection of the scalp, necessitates accurate etiological agent identification for effective treatment and epidemiological control.
- Conventional diagnostic methods for dermatophytes are often time-consuming, labor-intensive, and costly, driving the need for rapid and efficient alternatives.
- Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) offers potential for rapid fungal identification but typically requires a sub-culturing step, extending turnaround times.
Purpose of the Study:
- To develop and evaluate a novel MALDI-TOF MS protocol utilizing liquid cultures of dermatophytes to shorten the diagnostic turnaround time for tinea capitis.
- To assess the impact of using liquid cultures versus traditional solid cultures on the accuracy and speed of MALDI-TOF MS identification of dermatophytes.
- To investigate the influence of different spectral databases on the performance of the liquid culture MALDI-TOF MS protocol.
Main Methods:
- A standard MALDI-TOF MS protocol was adapted for use with liquid fungal cultures instead of conventional solid media.
- The performance of the liquid culture protocol was evaluated using three distinct reference spectral databases.
- Identification accuracy and turnaround time were compared between the developed liquid culture protocol and the standard solid culture protocol.
Main Results:
- The liquid culture MALDI-TOF MS protocol achieved a global correct identification rate of 62%, significantly lower than the 87% obtained with the solid culture protocol.
- A notable misidentification rate of 88% was observed for Trichophyton tonsurans when using liquid cultures, with isolates frequently misclassified as Trichophyton interdigitale.
- No significant difference in turnaround time was found between the liquid (11.6 days) and solid (11.7 days) culture protocols for primary isolates.
Conclusions:
- The developed liquid culture MALDI-TOF MS protocol did not significantly reduce the turnaround time for dermatophyte identification in tinea capitis cases.
- The reduced accuracy and lack of time-saving benefits indicate that a sub-culturing step remains essential for reliable MALDI-TOF MS identification of dermatophytes.
- The choice of culture medium and the quality of the reference database are critical factors influencing the accuracy and efficiency of MALDI-TOF MS diagnostics.
