Practical identification of eight medically important Trichosporon species by reverse line blot hybridization (RLB) assay and rolling circle amplification (RCA).

We developed a reverse line blot (RLB) hybridization-, and rolling circle amplification (RCA)-based assays for the identification of Trichoporon species and evaluated them with 48 isolates that had been previously recognized as belonging to eight species (Trichosporon asahii, T. cutaneum, T. dermatis, T. domesticum, T. inkin, T. japonicum, T. jirovecii, and T. laibachii). Results were compared to those obtained with DNA sequencing of three rRNA gene loci, i.e., the internal transcribed spacer (ITS) region, D1/D2 domain of the 28S rRNA gene and intergenic spacer 1 (IGS1) region. Using species-specific, or group-specific probes targeted at the ITS region and the D1/D2 domain, the RLB assay permitted accurate species identification of all 48 isolates with 100% specificity. Species-specific RLB probes correctly assigned 45/48 (94%) of the isolates (six species) with the exception of T. dermatis and T. japonicum isolates which were not targeted by the assay. Identification of T. dermatis relied on a positive hybridization result with the group-specific probe hybridizing with T. dermatis and T. jirovecii and the absence of a signal with the T. jirovecii-specific probe. T. japonicum strains were first assigned to the T. asahii-T. japonicum group by hybridization with the two species group-specific probe and then as T. japonicum by the absence of signal with a T. asahii-specific probe. Twelve species-specific RCA probes targeting the eight species studied detected templates of all 48 Trichosporon isolates and an artificial template of T. asteroides, all with good specificity. Both RLB and RCA are potential alternatives to DNA sequencing for the identification of Trichosporon species. The RLB approach is suited for the batched simultaneous analysis of large numbers of isolates, while RCA is more appropriate for the immediate study of single isolates. Comparative costs are US$7 and US$2 per assay for the RLB and RCA methods, respectively.