No abstract

Although the use of two "group-specific" probes targeting both the ITS1 and the ITS2 regions were required to identify T. soudanense, the other species were identified by single ITS1-or ITS2-targeted species-specific probes. There was good agreement between ITS sequencing and the RCA assay. Despite limited genetic variation between Trichophyton spp., the sensitive, specific RCA-based SNP detection assay showed potential as a simple, reproducible method for the rapid (2-h) identification of Trichophyton spp.

16S rDNA sequence analysis is the most accurate method for definitive species identification of nocardiae. However, conflicting results can be found due to sequence errors in gene databases. This study tested the feasibility of species identification of Nocardia by partial (5’-end 606-bp) 16S rDNA sequencing, based on sequence comparison with “reference” sequences of well-annotated strains. This new approach was evaluated using 96 American Type Culture Collection (n=6), and clinical (n=90) Nocardia isolates. Nucleotide sequence-based polymorphisms within species were indicative of “sequence types” for that species. Sequences were compared with those in the GenBank, Bioinformatics Bacteria Identification and Ribosomal Database Project databases. Compared with the reference sequence set, all 96 isolates were correctly identified using the criterion of ≥99% sequence similarity. Seventy-eight (81.3%) were speciated by database comparison; alignment with reference sequences resolved the identity of 14 (15%) isolates whose sequences yielded 100% similarity to sequences in GenBank under >1 species designation. Of 90 clinical isolates, the commonest species was Nocardia nova (33.3%) followed by Nocardia cyriacigeorgica (26.7%). Recently-described or uncommon species included Nocardia veterana (4.4%), Nocarida bejingensis (2.2%) and, Nocardia abscessus and Nocardia arthriditis (each n=1). Nocardia asteroides sensu stricto was rare (n=1). There were nine sequence types of N. nova, three of Nocardia brasiliensis with two each of N. cyriacigeorgica and Nocardia farcinica. Thirteen novel sequences were identified. Alignment of sequences with reference sequences facilitated species identification of Nocardia and allowed delineation of sequence types within species, suggesting that such a barcoding approach can be clinically useful for identification of bacteria.