Identification of Mycbacterium avium and Mycobacterium intracellulare/chimaera in clinical practice using probe data of the Xpert MTB/RIF assay
(2017) ECCMID 2017 — Location: Vienne (22.April.2017)
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- Background: Identification of non-tuberculosis mycobacteria (NTM) remains a major challenge in clinical practice, and requires specific tools such as sequencing, MALDI-TOF MS or commercial molecular assays for accurate diagnosis. Mycobacterium avium and M. intracellulare are regularly involved in human infections, particularly among severely immunocompromised patients. M. chimaera has recently been reported as a cause of health-care associated endocarditis, and is very similar genetically to M. intracellulare. In our clinical practice, we performed Xpert MTB/RIF© PCR on all MGIT cultures after confirmation of the presence of a mycobacterium by fluorescence microscopy. The principle of this test is based on the amplification of the Rifampicin Resistance Determining Region (RRDR) and the binding of 5 different segments by molecular-beacon probes names A, B, C, D and E. In our experience, approximately 50% of positive cultures are negative for M. tuberculosis (MTB), and identification of NTM is performed by rpoB sequencing or MALDI-TOF MS. Material/methods: We analysed the raw Probe results of 31 Xpert MTB/RIF tests performed on positive MGIT cultures for which an NTM was later confirmed and at least one Probe was positive (A, B, C, D or E). Results: All results could be classified within 3 different profiles determined by which of the 5 probes were positive. Among the 8 strains presenting an amplification of Probe A only, all were identified as M. intracellulare, M. chimaera or M. marseillense, three closely related species. Among the 14 strains which presented an amplification of Probe C only, different species were identified including M. gordonae (8), M. xenopi (3), M. simaie (1), M. fortuitum (1) and M. avium (1). Among the 9 strains presenting an amplification of both Probe C and Probe E, all were identified as M. avium. Conclusions: In our clinical experience, the analysis of Xpert MTB/RIF probe results allowed a correct identification of 3 important pathogenic NTM. These results were supported by the fact that there is a partial overlap of the RRDR region of the rpoB gene of MTB with other mycobacterial species. Further studies would be needed to better understand the clinical value of this observation.
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Colmant, A., Goeminne, L., TOUSSAINT, L., BRESSANT, F., Zitouni, A., TEYLAERT, M.-N., Vermeiren, M.-C., Martin, A., Simon, A., Kabamba-Mukadi, B., & André, E. (2017). Identification of Mycbacterium avium and Mycobacterium intracellulare/chimaera in clinical practice using probe data of the Xpert MTB/RIF assay. ECCMID 2017, Vienne. https://hdl.handle.net/2078.5/182442