Rapid Identification of the Mycobacterium tuberculosis Complex by Combining the ESAT-6/CFP-10 Immunochromatographic Assay and Smear Morphology

Abstract

Early secretory antigen 6 (ESAT-6) and cell filtrate protein 10 (CFP-10) are two antigens secreted as a complex by the replicating Mycobacterium tuberculosis complex (MTC). Recently, an immunochromatographic assay (ICA) using a monoclonal antibody against the ESAT-6/CFP-10 complex was developed for the purpose of MTC detection. In this study, the efficacy of the assay was tested with 603 BACTEC cultures that were incubated for 3 additional days after positive signals appeared in the BACTEC MGIT 960 system. Bacterial isolates were recovered from these 603 BACTEC cultures, and 332 MTC isolates, 270 nontuberculosis mycobacterial isolates, and 1 Nocardia isolate were identified by using standard biochemical assays. The ESAT-6/ CFP-10 assay detected 322 MTC cultures, resulting in a sensitivity of 97% and a specificity of 97.4%. To reduce the false-negative rate and improve the sensitivity, either serpentine cording in an acid-fast bacillus stain of the cultural smear, the ESAT-6/CFP-10 assay, or a combination of both was used for MTC detection. The sensitivity was then increased to 99.1%, and the negative predictive value increased to 98.9%, but the specificity decreased to 94.8% and the positive predictive value decreased to 95.9%. However, a combination of serpentine cording in cultural smears and the positivity of the ICA resulted in the specificity and positive predictive values of 100%. Therefore, BACTEC cultures with both serpentine cording and positivity of the ESAT-6/CFP-10 assay could be reported to contain MTC directly. The ESAT-6/CFP-10 assay may be an alternative of the Capilia assay (MPB64-ICA) as a convenient and cost-effective method for identification of MTC in culture.

Uveitis with occult choroiditis due to Mycobacterium kansasii: limitations of interferon-gamma release assay (IGRA) tests (case report and mini-review on ocular non-tuberculous mycobacteria and IGRA cross-reactivity)

“…Non-tuberculosis mycobacteria are subdivided into three groups of slow-growing strains (SGMs) where M. kansasii, M. marinum, M. szulgai and M. gordonae are included and one group of rapidly growing strains [15]. Ocular infections are mostly caused by M. abcessus and M. chelonae, a rapidly growing mycobacteria (RGM), which is mostly involved in keratitis reports [16][17][18] and which does not produce a positive IGRA test [19]. Moreover, tuberculosis-like chorioretinitis has also been reported in association with a non-characterised RGM [9].…”

Rapid identification of Mycobacterium tuberculosis complex in clinical isolates by combining presumptive cord formation and MPT64 Antigen Immunochromatographic Assay

“…These results are similar to those observed by Shen et al combining cord morphology with the Capilia TB assay for identification of MTB in MGIT positive tubes. 8,17 We therefore suggest that when the cultured smear shows serpentine cord morphology and is also found to be positive by ICT for MPT64 antigen, the culture can be reported to contain MTB complex. If both the presumptive cord formation and the ICT for MPT64 antigen test are negative, the culture should be reported to contain NTM.…”

Validation of nanodiamond-extracted CFP-10 antigen as a biomarker in clinical isolates of Mycobacterium tuberculosis complex in broth culture media

“…The detection limit could reach 90 ng/ml. The advantage of DND mass spectrometry techniques is that they can avoid the cross-reactivity found in immunochromatographic assays (ICA) [4]. In Figures 1 and 2, the mass spectra of MTC and NTM are clearly different from one another; therefore no cross-reactivity would occur with the mass spectrometry approach.…”

“…For example, the immunochromatographic assay (ICA) used the ESAT-6/CFP-10-specific monoclonal antibody to detect Mycobacterium tuberculosis complex (MTC) in the BACTEC MGIT 960 system (Formosa Biomedical Technology Corp., Taiwan) [4]. The ESAT-6/CFP-10 assay was a convenient and cost-effective method for identification of MTC with a sensitivity of 99.1% and a specificity of 94.8%.…”