Simple and rapid identification of the Mycobacterium tuberculosis complex by immunochromatographic assay using anti-MPB64 monoclonal antibodies

Evaluation of the Bactec MGIT 960 system in combination with the MGIT TBc identification test for detection of Mycobacterium tuberculosis complex in respiratory specimens

The sensitivity and specificity of the MGIT TBc identification (TBc ID) test for Mycobacterium tuberculosis complex (MTC) detection in positive Bactec MGIT cultures were 95.2% and 99.2%, respectively. When MTC-positive results obtained from two additional molecular methods were included, the sensitivity of the MGIT TBc ID test was 85.4%, while that of culture was 95.7%.

Evaluation of TBc identification immunochromatographic assay for rapid identification of Mycobacterium tuberculosis complex in samples from broth cultures

Tuberculosis (TB) is a disease of major public health concern worldwide, especially in developing countries. In addition, the human immunodeficiency virus (HIV) epidemic has increased the incidence of infection with nontuberculous mycobacteria (NTM). Rapid, accurate, and simple methods for differentiation of Mycobacterium tuberculosis complex (MTBC) isolates from NTM is greatly needed for successful control of the TB epidemic. This study was done to evaluate the clinical performance of the BD MGIT TBc identification test (TBc ID) for rapid identification of MTBC in samples from broth cultures. A total of 229 Ziehl-Neelsen (ZN) stain-positive MGIT cultures were tested using the TBc ID test, and the results were compared with those of the AccuProbe MTBC identification test (GenProbe, San Diego, CA). The agreement between the TBc ID test and the AccuProbe assay was 96% (kappa = 0.92; confidence interval [CI] = 0.869 to 0.971). The sensitivity, specificity, and negative and positive predictive values of the TBc ID test compared to the AccuProbe assay were 100%, 92.4%, 100%, and 92.2%, respectively. After additional molecular testing, the agreement between the two methods increased to 97.8% (kappa = 0.96; CI = 0.917 to 0.994), and the specificity and positive predictive value increased to 95.6% and 95.7%, respectively. The TBc ID test is a simple, sensitive, and specific test for identification of MTBC in samples from acid-fast bacillus (AFB) smear-positive cultures. The TBc ID test could be a good alternative to the AccuProbe test in TB diagnostic laboratories.

Assessment of the SD Bioline Ag MPT64 Rapid™ and the MGIT™ TBc identification tests for the diagnosis of tuberculosis

Successful control of tuberculosis relies on the rapid detection of Mycobacterium tuberculosis. Few chromatographic lateral flow assays for the discrimination of the M. tuberculosis complex were developed from culture media. We compared the values of 2 assays to assess their place in diagnosis of tuberculosis. We conclude of their efficiency and relevance to supplant the conventional methods.

[Evaluation of the SD BIOLINE TB Ag MPT64 Rapid® for the diagnosis of tuberculosis]

The purpose of this study was to evaluate the SD Bioline Ag MPT64 Rapid(®) for identification of the Mycobacterium tuberculosis complex. The method uses an immunochromatographic assay and needs 100 μl of sample taken from liquid culture or colonies suspended. The sensitivity was determined using 99 strains of M. tuberculosis complex and the specificity using 10 nontuberculous mycobacteria and 85 strains other than mycobacteria genus. The test showed excellent sensitivity (99%) and specificity (100%). This technique displays several advantages and is destined to spread in all laboratories and particularly in endemic areas.

Selection and application of peptide mimotopes of MPT64 protein in Mycobacterium tuberculosis

Antibody responses can be useful markers of tuberculosis (TB) infection, especially in the screening of extra-pulmonary TB. MPT64 is an important antigen in Mycobacterium tuberculosis (MTB) infection and is used in serological diagnosis. However, large variability in the diagnostic accuracy of MPT64 as a serological tool has limited its application. Phage-displayed random peptide libraries have emerged as a powerful technique to select peptides (epitopes) or mimotopes that may serve as surrogate diagnostic markers in serological tests. In the present study, this method was employed to identify mimotopes of the MPT64 protein of MTB by screening a linear heptapeptide library with rabbit antibodies raised against MPT64 protein. Two antigenic mimotopes (M2 and M6) resembling B-cell epitopes of MPT64 were identified that bound the affinity purified anti-MPT64 polyclonal antibodies and competed with MPT64 for antibody binding. From the results of sequence alignment and a structure modelling figure of MPT64, the sequence of the 2nd to 5th amino acids (DSML) of M2 was totally consistent with the sequence of the 224th to 227th amino acids of MPT64 and the peptide is located on the surface of the space structure of MPT64, suggesting that it might be a linear epitope of MPT64. The recognition of both phage-displayed and synthetic peptides of M2 by the anti-MPT64 polyclonal antibodies also supported this. Although no recurring sequence and no analogue to MPT64 of M6 were found for sequence alignment, the recognition of both phage-displayed and synthetic peptides of M6 by the anti-MPT64 polyclonal antibodies indicated that it might be a mimotope of a conformational epitope of MPT64. According to the results of the reactivity of human sera with synthetic M2 and M6 peptides and MPT64, M2 showed a significantly higher AUC and sensitivity than M6 and MPT64, especially for the sera from sputum-negative TB patients, suggesting that the M2 mimotope may be useful in serological diagnostic testing for TB.

Evaluation of the rapid MGIT TBc identification test for culture confirmation of Mycobacterium tuberculosis complex strain detection

A culture confirmation test for the detection of Mycobacterium tuberculosis complex strains that uses a lateral-flow immunochromatographic assay to detect the MPB64 antigen, the MGIT TBc identification (TBc ID) test, has been developed. We evaluated the performance of the TBc ID test in the detection of the M. tuberculosis complex in 222 primary-positive liquid cultures. We compared these results to those of nucleic acid-based identification and conventional biochemical tests. The validity of the TBc ID test was determined, and all of the nontuberculous mycobacteria (NTM) and Nocardia species tested were found to be negative. The detection limit of the TBc ID test was 5 × 10(5) CFU/ml, and for IS6110 real-time PCR it was 5 CFU/ml. All of the M. tuberculosis and M. africanum cultures were found to be positive, while M. bovis and M. bovis BCG cultures were negative. With the exception of 1 contaminated culture, the 221 culture-positive isolates contained 171 (77.5%) M. tuberculosis isolates, 39 (17.6%) NTM species, and 11 (5.0%) unidentified species. Two culture-positive isolates harbored a 63-bp deletion at position 196 of the mpb64 gene. The sensitivity, specificity, positive predictive values, and negative predictive values of the TBc ID test were 98.8, 100, 100, and 95.1%, respectively. Furthermore, the approximate turnaround time for real-time PCR was 4 h (including buffer and sample preparation), while for the TBc ID test it was less than 1 h. We suggest an algorithm for the primary identification of M. tuberculosis in liquid culture using the TBc ID test as an alternative to conventional subculture followed by identification using biochemical methods.

Evaluation of the Capilia TB assay for culture confirmation of Mycobacterium tuberculosis infections in Zambia and South Africa

The performance and cost of the Capilia TB assay were evaluated for use in a resource-limited setting. The sensitivity and specificity were 99.6% and 99.5%, respectively. The incremental costs of the Capilia test were estimated to be $1.46 and $1.84 when the test was added to liquid and solid culture processes, respectively. These findings suggest that the Capilia TB assay represents a rapid, simple, and inexpensive Mycobacterium tuberculosis identification test that can be used in resource-limited settings.

Fluorescent nanoparticle-based indirect immunofluorescence microscopy for detection of Mycobacterium tuberculosis

A method of fluorescent nanoparticle-based indirect immunofluorescence microscopy (FNP-IIFM) was developed for the rapid detection of Mycobacterium tuberculosis. An anti-Mycobacterium tuberculosis antibody was used as primary antibody to recognize Mycobacterium tuberculosis, and then an antibody binding protein (Protein A) labeled with Tris(2,2-bipyridyl)dichlororuthenium(II) hexahydrate (RuBpy)-doped silica nanoparticles was used to generate fluorescent signal for microscopic examination. Prior to the detection, Protein A was immobilized on RuBpy-doped silica nanoparticles with a coverage of ∼5.1×102 molecules/nanoparticle. With this method, Mycobacterium tuberculosis in bacterial mixture as well as in spiked sputum was detected. The use of the fluorescent nanoparticles reveals amplified signal intensity and higher photostability than the direct use of conventional fluorescent dye as label. Our preliminary studies have demonstrated the potential application of the FNP-IIFM method for rapid detection of Mycobacterium tuberculosis in clinical samples.

Concordance of variable-number tandem repeat (VNTR) and large sequence polymorphism (LSP) analyses of Mycobacterium tuberculosis strains

Variable-number tandem repeat (VNTR) and large sequence polymorphism (LSP) analyses were compared to determine whether VNTR analysis was effective for population genetic analysis of Mycobacterium tuberculosis strains. A total of 682 strains, 510 Beijing genotype and 172 non-Beijing genotype strains, were studied. The number of repeats was investigated for 24 VNTR loci: the 15 loci of "optimized miru", the 8 loci of "Beijing option", and 1 locus for "JATA12". Six loci (miru31, Mtub4, QUB4156c, QUB3232, VNTR3820, and VNTR4120) showed significantly different median numbers of repeats in strains belonging to different lineages defined by LSP (P<0.01, Mann-Whitney U test). When a minimum-spanning tree (MST) was reconstructed using these 6 loci, most strains clustered in the expected branches in the MST branches. However, topology of the MST was not congruent with the evolutional hypothesis of M. tuberculosis, indicating that MST analysis using VNTR data should not use for phylogeny of the organism. When the standardized index of association (sI(A)) was calculated using data for the 6 VNTR loci, the value of sI(A) was significantly different from zero (Monte Carlo simulation with 10,000 resamplings) in every lineage, indicating the linkage disequilibrium in different lineage strains of M. tuberculosis. These results were consistent with the hypothesis that clonal evolution of lineages of the organism has occurred. Therefore, the 6 loci identified in this study would be effective for M. tuberculosis population genetic analysis due to their significantly different median numbers of repeat and linkage disequilibrium though VNTR data was not effective for phylogeny of the organism.

Evaluation of an immunochromatographic assay kit for rapid identification of Mycobacterium tuberculosis complex in clinical isolates

We evaluated a new immunochromatographic assay (ICA) using mouse monoclonal anti-MPT64 antibody for rapid discrimination between Mycobacterium tuberculosis and nontuberculous mycobacteria in clinical isolates. A study with mycobacteria and other organisms showed excellent sensitivity (approximately equal 99%) and specificity (100%) and an appropriate detection limit (10(5) CFU/ml) when tested with M. tuberculosis H37Rv. This ICA can simplify the identification of M. tuberculosis in clinical laboratories.

Biological and molecular characteristics of Mycobacterium tuberculosis clinical isolates with low-level resistance to isoniazid in Japan

We reevaluated the BACTEC MGIT 960 antimicrobial susceptibility testing system (MGIT 960 AST) by using 1,112 isolates of Mycobacterium tuberculosis. When the results of MGIT 960 AST were compared with that of the proportion method using Ogawa medium (Ogawa PM), discrepant results were obtained for 30 strains with isoniazid, all resistant by MGIT 960 AST but susceptible by Ogawa PM. For 93% of the strains that produced discrepant results, the MIC was 0.4 or 0.8 microg/ml, showing resistance by the proportion method using Middlebrook agar plates. Furthermore, it was also established by analyses of the katG and inhA genes that strains resistant only by MGIT 960 AST have a low level of isoniazid (INH) resistance, indicating that MGIT 960 AST is a reliable method. Ninety-six strains were resistant to 0.1 microg/ml INH by MGIT 960 AST. When they were divided into three groups, Low-S (susceptible at 0.2 microg/ml), Low-R (resistant at 0.2 microg/ml), and High-R (resistant at 1.0 microg/ml), by Ogawa PM, 43.3% of the Low-S strains had mutations in the promoter region of inhA and no mutations were detected in katG codon 315, while 61.7% of the High-R strains had katG codon 315 mutations or a gross deletion of katG. These results suggest that mutations in inhA are associated with low-level resistance to INH and katG codon 315 mutations are associated with high-level resistance to INH. In addition, the analyses demonstrated some relationship of mutations in the inhA gene with ethionamide resistance for the Low-S strains, but not for the High-R strains.

Performance assessment of the Capilia TB assay and the BD ProbeTec ET system for rapid culture confirmation of Mycobacterium tuberculosis

Because of the increasing numbers of nontuberculous mycobacterial isolates from clinical specimens, rapid and accurate methods for culture confirmation of Mycobacterium tuberculosis are urgently needed. The study evaluated the performance of the Capilia TB immunochromatographic assay (TAUNS, Numazu, Japan) for culture confirmation of M. tuberculosis using 242 culture-positive liquid media in 2 mycobacterial laboratories from November 2005 to February 2006. Among the 242 samples, 183 were also tested with the BD ProbeTec ET (CTB) assay (Becton Dickinson, Sparks, MD). The results of both assays were compared to the culture results and to each other. The overall sensitivity and specificity of the Capilia TB assay were 98.6% and 97.9%, respectively, and for the CTB assay were 97.3% and 97.1%, respectively. The positive and negative predictive values for the Capilia TB assay were 98.6% and 97.9%, respectively, and for the CTB assay were 98.2% and 95.8%, respectively. Among the 183 samples tested with both assays, 8 had discrepant results, including Capilia-TB-false-positive in 2, CTB-false-positive in another 2, CTB-false-negative in 2, Capilia TB-false-negative in 1, and both assays with false-negative results in the remaining one. This study demonstrated that the Capilia TB assay has a similar diagnostic value with the CTB assay. In addition, with the immunochromatographic method, it is less time-consuming and does not require other laboratory equipment.

Facing the crisis: improving the diagnosis of tuberculosis in the HIV era

Although the human immunodeficiency virus (HIV) infection pandemic has had a catastrophic impact on tuberculosis (TB) control efforts, especially in sub-Saharan Africa, most of the fundamental concepts reflected in the directly observed treatment, short course (DOTS) strategy still hold true in the HIV era. What has changed, and dramatically, is the importance of speedy and accurate TB diagnosis and the difficulty of achieving this. The disproportionate amount of smear-negative disease in sub-Saharan Africa, which shoulders two-thirds of the global burden of HIV infection and acquired immunodeficiency syndrome, has greatly complicated TB case detection and disease control. Now, 15 years after TB rates began to soar in countries where HIV infection is prevalent, we have learned that the conventional approach -- passively waiting for patients with advanced symptomatic disease to make their way to microscopy centers for diagnosis -- has disastrous consequences. Without better diagnostic tools for TB and effective strategies for their implementation, transmission will not be interrupted, mortality will not be checked, and TB will not be controlled in areas where HIV infection is prevalent. Fortunately, a number of technical opportunities exist for the creation of improved diagnostic tests. Developing and exploiting such tests to support TB control in HIV-infected populations is an urgent priority. A substantial public sector effort is under way to work in partnership with the biotechnology industry to accelerate progress toward that goal. In this article, we will define the need for better TB tests and describe technologies being developed to meet that need.

Mutations including IS6110 insertion in the gene encoding the MPB64 protein of Capilia TB-negative Mycobacterium tuberculosis isolates

A simple immunochromatographic assay, Capilia TB, using anti-MPB64 monoclonal antibodies, is a kit for discriminating between the Mycobacterium tuberculosis complex and mycobacteria other than tubercle bacilli. The sensitivity of the kit was estimated to be 99.2% (381 of 384 samples). The sequencing analysis revealed that all of the Capilia TB-negative isolates had mutations within the mpb64 gene, leading to the production of an incomplete protein as a result of a deletion of the C-terminal region of the protein.

Use of molecular methods to identify the Mycobacterium tuberculosis complex (MTBC) and other mycobacterial species and to detect rifampin resistance in MTBC isolates following growth detection with the BACTEC MGIT 960 system

A prospective study was organized by using a total of 1,585 consecutive clinical specimens to determine whether biomass obtained from positive growth in the MGIT 960 system could be used directly in AccuProbe DNA hybridization tests, the PCR-based Inno-LiPA Rif.TB (LiPA) assay, and a PCR-based DNA sequencing of the rpoB gene for the rapid identification of the Mycobacterium tuberculosis complex (MTBC) and other mycobacterial species and for the determination of rifampin (RIF) resistance in MTBC strains. The results were compared to routine culture, identification, and susceptibility testing techniques performed on the same samples. The study results revealed that the DNA AccuProbe assay (on the day of growth positivity) readily identified 95.7%, the LiPA assay readily identified 98.6%, and rpoB sequencing readily identified 97.1% of the 70 MTBC isolates from mycobacterial growth indicator tubes (MGIT). In addition, application of the LiPA for the identification and RIF susceptibility testing of the MTBC in growth-positive MGIT resulted in a turnaround time of less than 2 weeks after specimen receipt. Although DNA sequencing of rpoB required a slightly longer (16 days) turnaround time, this method was capable of identifying several species of nontuberculous mycobacteria in addition to identifying MTBC and determining RIF susceptibility or resistance. The molecular methods were also found to rapidly identify RIF-susceptible and -resistant MTBC in two of the three mixed mycobacterial cultures weeks earlier than conventional methods. In conclusion, the biomass obtained in MGIT at the time of growth positivity in the 960 system is sufficient for use in all three molecular tests, and this approach can reduce the turnaround time for reporting results.

Improved serodetection of Mycobacterium bovis infection in badgers (Meles meles) using multiantigen test formats

Despite attempts to control bovine tuberculosis, the incidence of disease in Great Britain continues to rise. In GB, the European badger (Meles meles) is a reservoir of infection with Mycobacterium bovis. In an effort to improve the serodetection of badger tuberculosis, we examined sera from M. bovis culture-positive and culture-negative badgers for their ability to recognize M. bovis antigens, using a multi-antigen print immunoassay (MAPIA). Depending on the antigens used in the MAPIA, the assay had a sensitivity of 49-59% and a specificity of 84-88% Results from the MAPIA were used to select antigens for the development of a lateral-flow immunoassay. This so-called 'Rapid Test' used 5microl of serum and gave unambiguous results within 10 min. When applied to 178 badger sera, the Rapid Test had a sensitivity of 53% and a specificity of 95%. This represented an improvement over the performance of the existing ELISA Test, which had a sensitivity of 47% and a specificity of 89% on the same sera. This is the first report of a diagnostic test for badger tuberculosis that can be performed alongside the captive animal.

Evaluation of BACTEC MGIT 960 PZA medium for susceptibility testing of Mycobacterium tuberculosis to pyrazinamide (PZA): compared with the results of pyrazinamidase assay and Kyokuto PZA test

The fully automated BACTEC MGIT 960 PZA medium for susceptibility testing of Mycobacterium tuberculosis to pyrazinamide (PZA) was evaluated using 101 Mycobacterium tuberculosis clinical isolates. The results obtained with the system were compared with those of the pyrazinamidase (PZase) assay and the Kyokuto PZA test based on a broth culture, which is commercially available in Japan. The overall concordance rate was 90.1% (91/101) among the three methods in the initial test. The concordance rates between the BACTEC MGIT 960 PZA medium vs the PZase assay, the BACTEC MGIT 960 PZA medium vs the Kyokuto PZA test, and the PZase assay vs the Kyokuto PZA test were 93.1, 91.1, and 96.0%, respectively. On the repeat test of the 10 strains with discrepant results among the three methods, the concordance rates reached over 97% between each of the two systems. The results of the repeat test were confirmed by MIC testing and sequencing analysis of the pncA gene encoding PZase of M. tuberculosis. The mean turnaround times from incubation for PZA susceptibility testing were almost similar for the two methods based on liquid media, the BACTEC MGIT 960 PZA medium and the Kyokuto PZA test (7.7 and 7.4 days, respectively). These results indicate that both methods based on liquid media, the fully automated BACTEC MGIT 960 PZA medium and the Kyokuto PZA test for susceptibility testing to PZA, are useful for rapid diagnosis of PZA resistant tuberculosis.

New simple and rapid test for culture confirmation of Mycobacterium tuberculosis complex: a multicenter study

Mycobacterial antigen MPB64 has been identified as a Mycobacterium tuberculoisis complex-specific secretory protein since 1984. Recently, a simple culture confirmation test for M. tuberculosis complex has been developed by using lateral flow immunochromatographic assay (ICA) to detect MPB64 with anti-MPB64 monoclonal antibody. The current multicenter study evaluated the performance of an ICA slide test for MPB64 antigen in the clinical setting. Primary positive cultures from clinical specimens, as well as stock cultures, were tested. Approximately 100 microl of positive liquid culture medium or suspension made from colonies on solid medium was placed into the test well of the plastic slide devise, and the test was read after 15 min. No processing or instrumentation was required. A total of 304 mycobacterial isolates consisting of M. tuberculosis complex (171 isolates) and mycobacteria other than M. tuberculosis (MOTT) complex (133 isolates) belonging to 18 different species were tested. Growth in liquid media (Mycobacteria Growth Indicator Tube [MGIT] and Radiometric 12B), as well as in solid (Löwenstein-Jensen and Middlebrook 7H10 agar) media, was evaluated. Results were compared with those obtained with nucleic acid-based and/or high-pressure liquid chromatography identification. All MOTT were found to be negative on the ICA slide with no cross-reaction. All M. tuberculosis and M. africanum cultures were found to be positive, whereas the results of M. bovis and M. bovis BCG cultures were variable since some of the BCG strains are known to lack MPB64 antigen production. The results did not change with prolonged storage of cultures. This low-tech rapid test with high sensitivity and specificity could provide an alternative to currently available identification methods, particularly for recently introduced nonradiometric liquid culture systems such as MGIT.