Bayesian analysis of two methods MALDI-TOF-MS system and culture test in otomycosis infection

Abstract

Objective: Identification of otomycotic fungi using matrix-assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectroscopy (MS) and to quantify pervasive errors with Bayes rule; values of sensitivity and specificity of culture test and MALDI-TOF-MS method are quantified. Method: Fungi cultured ear discharge samples were identified with culture test and MALDI-TOF-MS system. Minimum inhibitory concentration (MIC) or MEC (minimum effective concentration) for 6 antifungals were determined by antifungal susceptibility testing in vitro. With Bayes rule, sensitivity and specificity of both MALDI-TOF MS and culture test methods were computed. Results: Cultures yielded 42 fungal isolates which were confirmed as species (specified against each species) belonging to 8 genera, A. niger 22, Candida sp. 7, A. fumigatus 3, A. flavus 3, mixed Aspergillus sp. 3, Mucor sp. 2, Rhizopus sp. 1, and Scopulariopsis sp.1; and MALDI-TOF-MS system also confirmed those isolates. In vitro antifungal susceptibility testing with terms of MIC 50 and MIC 90, isolates fungi were highly susceptible to 6 antifungals; and caspofungin was the most active antifungal. The high value of specificity 84.6%, suggested a limited loss of confidence on the culture test at the absence of an infection, in comparison to MALDI-TOF-MS. Sensitivity of the culture test was 87.5%; this high figure strongly approves the culture test to be the dependable method for the otomycosis diagnosis, when the infection is stable. Conclusion: Based on sensitivity and specificity together the culture test could be done in face of the gold-standard MALDI-TOF-MS system the estimating both methods. Keywords: Otomycosis, MALDI-TOF-MS system, Identification at species level, Sensitivity, Specificity