Rapid characterization of Mycobacterium fortuitum-chelonei complex by restriction fragment length polymorphism of ribosomal RNA genes

Novel algorithm identifies species in a polymycobacterial sample by fluorescence capillary electrophoresis-based single-strand conformation polymorphism analysis

An algorithm to directly identify multiple mycobacterial species in a sample by using fluorescence capillary electrophoresis (FCE)-based single-strand conformation polymorphism (SSCP) analysis was developed. Part of the 16S-23S ribosomal DNA internal transcribed spacer (ITS) region in 37 reference strains and 73 clinical isolates representing 19 mycobacterial species and Mycobacterium tuberculosis complex was PCR amplified with a fluorescence-labeled mycobacterium-specific primer, 6-carboxyfluorescein-labeled primer Sp1f, and 5-hexachlorofluorescein-tagged Sp2r. FCE-SSCP analysis was applied to both undigested PCR products and the corresponding HaeIII-digested restriction fragments (RF) from each strain. The 23 resultant SSCP patterns distinguished all 19 species and M. tuberculosis complex. The technique is applicable for the detection of multiple mycobacterial species in a sample. It was demonstrated by analyzing two model mycobacterial communities consisting of five species with both rapidly and slowly growing species (model A) and four species commonly encountered in clinical practice (model B). The sensitivity study with spiked sputum samples with different amounts of M. tuberculosis H37Rv, M. avium, and M. intracellulare cells indicated that up to 25% of the amount of each mycobacterium could be detected relative to the two other species. Fifty-one sputum specimens analyzed by FCE-RF-SSCP were compared with the Amplicor assay (Roche Diagnostics GmbH). Species identified by both assays were always the same. Moreover, FCE-RF-SSCP could identify M. abscessus and M. kansasii, which are not targeted by Amplicor. FCE-RF-SSCP of sputum obtained from a patient with mixed M. avium and M. intracellulare infection gave SSCP patterns corresponding to these two species.

Differentiation of mycobacterial species by PCR-restriction analysis of DNA (342 base pairs) of the RNA polymerase gene (rpoB)

PCR amplification-restriction analysis (PRA) of rpoB DNA (342 bp), which comprises the Rif(r) region, was used for the differential identification of 49 mycobacteria. The DNA had been used previously for the identification of mycobacterial species by comparative sequence analysis (B. J. Kim et al., J. Clin. Microbiol. 37:1714-1720, 1999). Digestion with four restriction enzymes (HaeIII, HindII, MvaI, and AccII), which were selected on the basis of rpoB DNA sequences, generated distinctive PRA patterns that allowed not only the reference strains but also the clinical isolates of mycobacteria to be distinguished. Both rapidly and slowly growing mycobacteria were distinctly differentiated by HaeIII digestion of the amplified rpoB DNA. By HindII digestion the Mycobacterium tuberculosis complex was distinguished from the other mycobacteria. Furthermore, six subspecies of Mycobacterium kansasii (subspecies I to VI) as well as the closely related Mycobacterium gastri, and other closely related species, were distinguished by simultaneous digestion of MvaI and AccII. According to the rpoB PRA scheme, 240 strains of clinical isolates could be identified. It was also possible to detect and identify M. tuberculosis directly from sputa and bronchoalveolar lavage specimens. These results suggest that PRA of rpoB DNA is a simple and feasible method not only for the differentiation of culture isolates but also for the rapid detection and identification of pathogenic mycobacteria in primary clinical specimens.

A rapid and gentle method for the isolation of genomic DNA from mycobacteria

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