ABSTRACT
Yeasts of the genus Malassezia have been associated with a variety of dermatological disorders in humans and domestic animals. With the recent recognition of new members of the genus, new questions are emerging with regard to the pathogenesis and epidemiology of the new species. As new species are recognized, a precise and comprehensive identification system is needed. Herein is described a bead suspension culture-based array that combines the specificity and reliability of nucleic acid hybridization analysis with the speed and sensitivity of the Luminex analyser. The developed 16-plex array consisted of species- and group-specific capture probes that acted as 'microcodes' for species identification. The probes, which were designed from sequence analysis in the D1/D2 region of rRNA and internal transcribed spacer (ITS) regions, were covalently bound to unique sets of fluorescent beads. Upon hybridization, the biotinylated amplicon was detected by the addition of a fluorochrome coupled to a reporter molecule. The hybridized beads were subsequently analysed by flow cytometric techniques. The developed array, which allowed the detection of species in a multiplex and high-throughput format, was accurate and fast, since it allowed precise identification of species and required less than 1 h following PCR amplification. The described protocol, which can integrate uniplex or multiplex PCR reactions, permitted the simultaneous detection of target sequences in a single reaction, and allowed single mismatch discrimination between probe and non-target sequences. The assay has the capability to be expanded to include other medically important pathogenic species in a single or multiplex array format.
Subject(s)
DNA, Fungal/genetics , Flow Cytometry , Malassezia/classification , Nucleic Acid Hybridization , Animals , DNA, Fungal/analysis , DNA, Fungal/isolation & purification , DNA, Ribosomal/genetics , DNA, Ribosomal Spacer/genetics , Dermatomycoses/microbiology , Female , Humans , Malassezia/genetics , Male , Oligonucleotide Probes , Phylogeny , Polymerase Chain Reaction , Reproducibility of Results , Sensitivity and Specificity , Time FactorsABSTRACT
A multicenter study was conducted to define the most suitable testing conditions for antifungal susceptibility of dermatophytes. Broth microdilution MICs of clotrimazole, itraconazole, and terbinafine were determined in three centers against 60 strains of dermatophytes. The effects of inoculum density (ca. 10(3) and 10(4) CFU/ml), incubation time (3, 7, and 14 days), endpoint criteria for MIC determination (complete [MIC-0] and prominent [MIC-2] growth inhibition), and incubation temperature (28 and 37 degrees C) on intra- and interlaboratory agreement were analyzed. The optimal testing conditions identified were an inoculum of 10(4) CFU/ml, a temperature of incubation of 28 degrees C, an incubation period of 7 days, and MIC-0.
