Two-Tube Multiplex PCR for Genotyping Tuberculous and Nontuberculous Mycobacterial Species in Pathology Specimens

Abstract

Background: The incidence of mycobacterial infection, in particular M. tuberculosis complex (MTC), is increasing in some Western countries, while nontuberculous mycobacteria (NTM) may be recognized more frequently in clinical specimens worldwide. The clinical scenario and available histopathology alone are often insufficient to separate these two categories of mycobacterial disease, whose behavior and treatment differ. In particular, NTM may be clinically unsuspected in pathological specimens and the opportunity for culturing missed. Methods: We developed two multiplex PCR assays, which distinguish MTC from NTM by detecting the IS6110 insert in the first tube and discriminating up to 14 NTM reference strains in the second by targeting the 16S-23S rRNA internal transcribed spacer. Test material included 594 routine clinical specimens with diverse pathology; many were granulomas unrelated to mycobacterial infection. About 75% were formalin-fixed paraffin blocks, the remainder mainly cytologic imprints or aspirates on FTA cards submitted on suspicion of mycobacterial infection either to avoid frozen sectioning (with the attendant risk of aerosolisation) or at the time of fine needle aspiration. Results: The paraffinized material yielded 53 MTC positives and the cytological 21 positives. A subset consisting of 337 specimens was also analyzed for NTM and yielded 51 positives. The frequency of simultaneous NTM infection in tuberculous patients was about 17%. Mycobacterium avium complex represented the dominant NTM species overall, showed a predilection for lung and lymph node, and together with M. haemophilum were the second most frequent NTM just behind M. ulcerans/M. marinum in skin and soft tissue, the category displaying the largest NTM diversity. Conclusions: Cytological and deparaffinized tissue analyzed in a new two-tube multiplex PCR allows for specific discrimination of causative agents in mycobacterial infection. MTC is readily distinguished from NTM for appropriate therapy, and NTM presumptively diagnosed at the species level allows appropriate choices of antimicrobials.