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

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.

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.

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.

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.