First-time detection and identification of the Mycobacterium tuberculosis Complex members in extrapulmonary tuberculosis clinical samples in south Tunisia by a single tube tetraplex real-time PCR assay.
PLoS Negl Trop Dis 2017;
11:e0005572. [PMID:
28475618 PMCID:
PMC5435359 DOI:
10.1371/journal.pntd.0005572]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 05/17/2017] [Accepted: 04/17/2017] [Indexed: 01/15/2023] Open
Abstract
Introduction
Tunisia has one of the highest burdens of extrapulmonary tuberculosis (EPTB) among tuberculosis (TB) cases but the contribution of MTBC-mediated human EPTB is unknown. EPTB diagnosis is challenging due to the paucibacillary nature of clinical samples. Therefore, a need of a simplified molecular method for sensitive and specific TB detection and differentiation of MTBC members caused EPTB remains a priority to an early diagnosis, optimize successful anti-TB treatment and minimize transmission. We evaluated the performance of a single tube tetraplex Taq Man real time PCR for EPTB detection and differentiation between MTBC members directly on extrapulmonary samples.
Materials and methods
Extrapulmonary samples obtained from clinically suspected EPTB patients from 2013 to April 2015 were tested by Ziehl Neelsen Staining, mycobacterial culture and qPCR assay for RD1, RD9, RD12 and ext-RD9 targets (MTBC-RD qPCR). The performance of qPCR was compared to a reference standard based on MTBC culture and/or at least two criteria of a composite reference standard (CRS) including clinical, radiological, histopathological and therapeutic findings.
Results
EPTB was identified in 157/170 (92.4%) of included patients of whom 99 (63%) were confirmed by culture and 58 (36.9%) by CRS criteria. The sensitivity and specificity of qPCR, in comparison to the reference standard were 100% (157/157) and 92.3% (12/13), respectively. The sensitivity of qPCR was statistically significant as compared to culture and smear microscopy (P< 0.001). QPCR results showed M. bovis identification in 77.1% of extrapulmonary samples in occurrence to lymphadenitis infection. M. tuberculosis and M.bovis BCG were detected in 21.6% and 1.3% of cases, respectively.
Conclusions
MTBC–RD qPCR proved to be a rapid and sensitive assay for simultaneously TB detection and MTBC members identification on extrapulmonary samples within 1.5 days after sample receipt. Its high sensitivity could make this method a useful tool in diagnosing TB in addition to routine conventional methods and TB clinical parameters.
Mycobacterial related EPTB diagnosis remains a challenge. In fact the paucibacillary nature of human specimens realized from inaccessible sites might be one of the causes giving a low sensitivity of routine used diagnostic tests. Therefore the use of Real time PCR (qPCR) contributes to a specific, sensitive and rapid EPTB diagnosis which helps to a successful anti TB treatment. However almost all the previous studies using qPCR to improve the molecular diagnosis of EPTB have focused only on positive culture materials or have identified only the Mycobacterium genus. Indeed, despite the relatively high occurrence of TB cases in Tunisia, there is no study available on EPTB related mycobacteria in southern Tunisia. Thus, our study is the first to evaluate a single tube tetraplex MTBC-RD qPCR in order to (i) detect and differentiate between the different MTBC members directly on EPTB specimens (ii) correlate qPCR results with a reference standard based on culture and/or at least two criteria of a composite reference standard (CRS) including clinical, radiological, histopathological and therapeutic findings. In our study, MTBC-RD qPCR was shown to give a high sensitivity and specificity compared to the reference standard. M. bovis is the major cause of EPTB in occurrence to lymphadenitis infection. Finally, M. bovis and M. tuberculosis were identified by qPCR among patients with negative culture being CRS positive for EPTB.
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