title: 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.
authors.affiliation: Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, Veterans General Hospital, Taichung, Taiwan, Republic of China.
authors.forename: Gwan-Han
authors.initials: GH
authors.lastname: Shen
authors.forename: Chien-Shun
authors.initials: CS
authors.lastname: Chiou
authors.forename: Shiau-Ting
authors.initials: ST
authors.lastname: Hu
authors.forename: Kun-Ming
authors.initials: KM
authors.lastname: Wu
authors.forename: Jiann-Hwa
authors.initials: JH
authors.lastname: Chen
mesh_terms: D000942:Antigens, Bacterial / Q000032:analysis*; D001426:Bacterial Proteins / Q000032:analysis*; D001431:Bacteriological Techniques / Q000379:methods*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008853:Microscopy / Q000379:methods; D009169:Mycobacterium tuberculosis / Q000166:cytology / Q000276:immunology*; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C117940:CFP-10 protein, Mycobacterium tuberculosis; C093276:ESAT-6 protein, Mycobacterium tuberculosis