Rapid identification of the Mycobacterium tuberculosis complex by combining the ESAT-6/CFP-10 immunochromatographic assay and smear morphology

Quantitation of Circulating Mycobacterium tuberculosis Antigens by Nanopore Biosensing in Children Evaluated for Pulmonary Tuberculosis in South Africa

Nanopore sensing of proteomic biomarkers lacks accuracy due to the ultralow abundance of targets, a wide variety of interferents in clinical samples, and the mismatch between pore and analyte sizes. By converting antigens to DNA probes via click chemistry and quantifying their characteristic signals, we show a nanopore assay with several amplification mechanisms to achieve an attomolar level limit of detection that enables quantitation of the circulating Mycobacterium tuberculosis (Mtb) antigen ESAT-6/CFP-10 complex in human serum. The assay's nonsputum-based feature and low-volume sample requirements make it particularly well-suited for detecting pediatric tuberculosis (TB) disease, where establishing an accurate diagnosis is greatly complicated by the paucibacillary nature of respiratory secretions, nonspecific symptoms, and challenges with sample collection. In the clinical assessment, the assay was applied to analyze ESAT-6/CFP-10 levels in serum samples collected during baseline investigation for TB in 75 children, aged 0-12 years, enrolled in a diagnostic study conducted in Cape Town, South Africa. This nanopore assay showed superior sensitivity in children with confirmed TB (94.4%) compared to clinical "gold standard" diagnostic technologies (Xpert MTB/RIF 44.4% and Mtb culture 72.2%) and filled the diagnostic gap for children with unconfirmed TB, where these traditional technologies fell short. We envision that, in combination with automated sample processing and portable nanopore devices, this methodology will offer a powerful tool to support the diagnosis of pulmonary TB in children.

Comparison of the Standard E TB-Feron ELISA and QuantiFERON-TB Gold PLUS assays: the advantageous use of whole recombinant protein antigens for latent tuberculosis diagnosis

The laboratory diagnosis of latent tuberculosis is often performed using interferon-gamma release assays. Here, we compared two enzyme-linked immunosorbent assay-based interferon-gamma release assays, namely, the newly developed Standard E TB-Feron enzyme-linked immunosorbent assay (STFE) and the QuantiFERON-TB Gold PLUS assay (QFT-GP), using samples from 155 participants. The STFE is based on using whole EAST6 and CFP10 recombinant antigens for latent tuberculosis diagnosis. The participants were classified into four groups and screened using both assays per the manufacturers' instructions. Thereafter, two statistical analyses were conducted to compare the obtained results. First, the STFE results were compared with the QTF-GP results (used as the gold standard) to calculate the total concordance, sensitivity, and specificity of STFE. Second, positivity and negativity concordances were calculated to differentiate healthy participants from participants with tuberculosis. The STFE showed 97% and 94% sensitivity and specificity, respectively. Furthermore, its positivity and negativity concordances were 91% and 98%, respectively. These results indicate the coordinated clinical performance of STFE in detecting latent tuberculosis and its improved performance in targeting tuberculosis-infected participants. Based on the comparison of the latent tuberculosis diagnostic abilities of STFE and QFT-GP, we establish the suitability and superior performance of STFE as a diagnostic tool.

The Usefulness of Bronchoscopy in the Diagnosis of Mycobacterium tuberculosis Complex Species Infection

BACKGROUND: Pulmonary tuberculosis is an active chronic infection of the lungs. It is still a public health problem globally caused by the Mycobacterium tuberculosis Complex (MTBC). These species are difficult to determine only by conventional tests. The clinical manifestations are almost similar between the strains and cause diagnosis delays. Prolonged and intolerable MTBC therapy inhibits infection control. AIM: This study aims to evaluate the usefulness of bronchoscopy in diagnosing the MTBC species infection. METHODS: This study recruited patients with difficulty expectorating sputum. Pulmonary tuberculosis was diagnosed with the Xpert MTB/RIF assay. This study assessed sputum Acid Fast Bacilli (AFB) staining, chest X-rays with active pulmonary tuberculosis, characteristics of Bronchoalveolar lavage (BAL), and bronchoscopic findings based on the Chung classification. The BAL of polymerase chain reaction analysis using RD9 and TbD1 primers to determine MTBC species. RESULTS: Out of the 30 cases, M. tuberculosis and Mycobacterium bovis 24 (80.0%) and 6 (20.0%) were identified in BAL fluid. There were 12 cases (40.0%) with AFB sputum test, and 25 (83.3%) of the Xpert MTB/RIF detected tuberculosis cases. All chest X-rays showed infiltrated and 22 (73.3%) pulmonary ectasis. There was a significant difference in MTBC species between sputum and BAL fluid (p < 0.05). The ulcerative type of bronchoscopy findings was significantly different in MTBC species (p < 0.05) and there was no macroscopic BAL fluid difference (p > 0.05). CONCLUSIONS: Bronchoscopy is a specimen collection technique that is beneficial in determining the diagnosis of MTBC. Analysis of BAL with molecular methods contributes to identifying MTBC species quickly and accurately.

Role of ESAT-6 in pathogenicity of Beijing and non-Beijing Mycobacterium tuberculosis isolates

BACKGROUND

Mycobacterium tuberculosis Beijing genotype was associated with tuberculosis outbreaks and increased transmissibility. To understand the variation in virulence between Beijing and non-Beijing clinical isolates of M.tuberculosis genotypes, the esat-6 gene sequencing, and its expression was compared in the macrophage environment.

MATERIALS & METHODS

Among 64 nonrepetitive, culture-positive M.tuberculosis, DNA extraction of 24 and 40 pure confirmed Beijing and non-Beijing isolates was accompanied by the boiling method. esat-6 gene PCR amplification and their sequencing were carried out by specific primers and its expression was performed on human macrophage cell line U937 after 6, 12, and 18 h of exposure to bacilli. The esat-6 mRNA transcription and expression in M. tuberculosis treated macrophage by Real-Time PCR and Western blot method.

RESULTS

Data analysis based on sequencing of the east-6 gene PCR product showed that this gene exists in all isolates and there are no changes or single nucleotide variation between the Beijing and non-Beijing isolates. In Beijing strains, the esat-6 expression was increased during the study times, but it was constant in non-Beijing isolates. esat-6 gene expression in Beijing isolates reached to about 44.9 times more than non-Beijing isolates after 18 h incubation on the macrophages cell line.

CONCLUSION

esat-6 is a conserved gene both in Beijing and non-Beijing isolates of M.tuberculosis. More expression of the east-6 gene in the macrophage model may indicate that this gene is likely to play a more important role in increasing the pathogenicity of Beijing strains.

Immune Biomarkers for Diagnosis and Treatment Monitoring of Tuberculosis: Current Developments and Future Prospects

Tuberculosis (TB) treatment monitoring is paramount to clinical decision-making and the host biomarkers appears to play a significant role. The currently available diagnostic technology for TB detection is inadequate. Although GeneXpert detects total DNA present in the sample regardless live or dead bacilli present in clinical samples, all the commercial tests available thus far have low sensitivity. Humoral responses against Mycobacterium tuberculosis (Mtb) antigens are generally low, which precludes the use of serological tests for TB diagnosis, prognosis, and treatment monitoring. Mtb-specific CD4⁺ T cells correlate with Mtb antigen/bacilli burden and hence might serve as good biomarkers for monitoring treatment progress. Omics-based techniques are capable of providing a more holistic picture for disease mechanisms and are more accurate in predicting TB disease outcomes. The current review aims to discuss some of the recent advances on TB biomarkers, particularly host biomarkers that have the potential to diagnose and differentiate active TB and LTBI as well as their use in disease prognosis and treatment monitoring.

Trends in Diagnosis for Active Tuberculosis Using Nanomaterials

Background:

Tuberculosis (TB), one of the leading causes of death worldwide, is difficult to diagnose based only on signs and symptoms. Methods for TB detection are continuously being researched to design novel effective clinical tools for the diagnosis of TB.

Objective:

This article reviews the methods to diagnose TB at the latent and active stages and to recognize prospective TB diagnostic methods based on nanomaterials.

Methods:

The current methods for TB diagnosis were reviewed by evaluating their advantages and disadvantages. Furthermore, the trends in TB detection using nanomaterials were discussed regarding their performance capacity for clinical diagnostic applications.

Results:

Current methods such as microscopy, culture, and tuberculin skin test are still being employed to diagnose TB, however, a highly sensitive point of care tool without false results is still needed. The utilization of nanomaterials to detect the specific TB biomarkers with high sensitivity and specificity can provide a possible strategy to rapidly diagnose TB. Although it is challenging for nanodiagnostic platforms to be assessed in clinical trials, active TB diagnosis using nanomaterials is highly expected to achieve clinical significance for regular application. In addition, aspects and future directions in developing the high-efficiency tools to diagnose active TB using advanced nanomaterials are expounded.

Conclusion:

This review suggests that nanomaterials have high potential as rapid, costeffective tools to enhance the diagnostic sensitivity and specificity for the accurate diagnosis, treatment, and prevention of TB. Hence, portable nanobiosensors can be alternative effective tests to be exploited globally after clinical trial execution.

Selection of DNA aptamers against Mycobacterium tuberculosis Ag85A, and its application in a graphene oxide-based fluorometric assay

The Mycobacterium Ag85 complex is the major secretory protein of M. tuberculosis. It is a potential marker for early diagnosis of tuberculosis (TB). The authors have identified specific aptamers for Ag85A (FbpA) via protein SELEX using magnetic beads. After twelve rounds of selection, two aptamers (Apt8 and Apt22) were chosen from different groups, and their binding constants were determined by flow cytometry. Apt22 (labeled with Atto 647N) binds to FbpA with high affinity (K_d = 63 nM) and specificity. A rapid, sensitive, and low-cost fluorescent assay was designed based on the use of Apt22 and graphene oxide, with a limit of detection of 1.5 nM and an analytical range from 5 to 200 nM of FbpA. Graphical abstract Schematic illustration of graphene oxide-based aptasensor for fluorometric determination of FbpA.

Preparation of immunochromatographic strips for rapid detection of early secreted protein ESAT-6 and culture filtrate protein CFP-10 from Mycobacterium tuberculosis

The early secreted protein early secretory antigenic target 6(ESAT-6) and the culture filtrate protein 10 (CFP-10) are 2 antigens that are specific to Mycobacterium tuberculosis. These 2 antigens are good targets for tuberculosis (TB) detection.To rapidly diagnose TB across a variety of samples, we developed colloidal gold immunochromatographic strips (ICSs) based on ESAT-6 and CFP-10.The strips were evaluated using 233 samples, including sputum, plasma, and pleural effusion samples.The positive detection rates for ICSs for ESAT-6 and CFP-10 in sputum (culture-positive for M tuberculosis) were 100% and 91.2%, respectively. The positive detection rates for ICSs for ESAT-6 and CFP-10 in plasma were 34.1% and 29.4%, respectively. The positive detection rates for ICSs for ESAT-6 and CFP-10 in pleural effusion were 64.7% and 55.9%, respectively. Experimental analysis of culture supernatant showing that the ICS developed for ESAT-6 had a sensitivity of 100% and a specificity of 91.2%. While the ICS developed for CFP-10 had a sensitivity of 91.2% and a specificity of 88.2%.The validity of the test is limited by source of sample. The technique is sensitive and specific for samples in sputum and culture media but not for plasma or pleural effusion samples. Detection of M tuberculosis using ICSs is rapid, simple, and relatively effective; thus, ICSs are a potential screening tool for TB.

Comparison of the Performance of Urinary Mycobacterium tuberculosis Antigens Cocktail (ESAT6, CFP10, and MPT64) with Culture and Microscopy in Pulmonary Tuberculosis Patients

Pulmonary tuberculosis (TB) is a major global health problem and is one of the top 10 causes of death worldwide. Our study aimed to evaluate the performance of urinary Mycobacterium tuberculosis (Mtb) antigens cocktail (ESAT6, CFP10, and MPT64) compared with culture and microscopy. This descriptive cross-sectional study was conducted in Dr. Hasan Sadikin General Hospital, Bandung, from January 2014 to October 2016. A total of 141 pulmonary tuberculosis patients were included. Sputum samples were examined for acid-fast bacilli (ZN stain) and mycobacterial culture (LJ); the Mtb antigens cocktail was examined in the urine sample. The positivity rate of TB detection from the three methods was as follows: AFB 52/141 (36.9%), culture 50/141 (35.5%), and urinary Mtb antigens cocktail 95/141 (67.4%). Sensitivity, specificity, PPV, and NPV of urinary Mtb antigens cocktail were 68.2%, 33%, 31.6%, and 69.6%, respectively. Validity of combination of both methods with culture as a gold standard yielded sensitivity, specificity, PPV, and NPV of 90%, 28.6%, 40.9%, and 83.8%, respectively. Combination of urinary Mtb antigens cocktail with AFB as a screening test gives a good sensitivity, although the specificity is reduced. Urinary Mtb antigens cocktail can be used as screening test for pulmonary tuberculosis.

Early detection of the growth of Mycobacterium tuberculosis using magnetophoretic immunoassay in liquid culture

Tuberculosis (TB) is an often neglected, epidemic disease that remains to be controlled by contemporary techniques of medicine and biotechnology. In this study, a nanoscale sensing system, referred to as magnetophoretic immunoassay (MPI) was designed to capture culture filtrate protein (CFP)-10 antigens effectively using two different types of nanoparticles (NPs). Two specific monoclonal antibodies against CFP-10 antigen were used, including gold NPs for signaling and magnetic particles for separation. These results were carefully compared with those obtained using the commercial mycobacteria growth indicator tube (MGIT) test via 2 sequential clinical tests (with ca. 260 clinical samples). The sensing linearity of MPI was shown in the range of pico- to micromoles and the detection limit was 0.3pM. MPI using clinical samples shows robust and reliable sensing while monitoring Mycobacterium tuberculosis (MTB) growth with monitoring time 3-10 days) comparable to that with the MGIT test. Furthermore, MPI distinguished false-positive samples from MGIT-positive samples, probably containing non-tuberculous mycobacteria. Thus, MPI shows promise in early TB diagnosis.

Bacterial pili, with emphasis on Mycobacterium tuberculosis curli pili: potential biomarkers for point-of care tests and therapeutics

CONTEXT

Novel biomarkers are essential for developing rapid diagnostics and therapeutic interventions Objective: This review aimed to highlight biomarker characterisation and assessment of unique bacterial pili.

METHODS

A PubMed search for bacterial pili, diagnostics, vaccine and therapeutics was performed, with emphasis on the well characterised pili.

RESULTS

In total, 46 papers were identified and reviewed.

CONCLUSION

Extensive analyses of pili enabled by advanced nanotechnology and whole genome sequencing provide evidence that they are strong biomarker candidates. Mycobacterium tuberculosis curli pili are emphasised as important epitopes for the development of much needed point-of-care diagnostics and therapeutics.

A silicon nitride ISFET based immunosensor for Ag85B detection of tuberculosis

A silicon nitride Ion Sensitive Field Effect Transistor (ISFET) based immunosensor was developed as a low-cost and label-free electrical detection for the detection of antigen 85 complex B (Ag85B). The sensing membrane of the ISFET was modified with 3-aminopropyltriethoxysilane (APTES) followed by glutaraldehyde (GA), yielding an aldehyde-terminated surface. This group is available for immobilization of a monoclonal antibody against a recombinant Ag85B protein (anti-Ag85B antibody). The optimal concentration for anti-Ag85B antibody immobilization onto the modified ISFET was 100 μg ml^-1. This optimal condition provided the maximal binding capability and minimal non-specific background signal. The binding event between the recombinant Ag85B antigen and anti-Ag85B antibody on the ISFET surface is presented by monitoring the gate potential change at a constant drain current. The dose response for the recombinant Ag85B protein showed a linear response between 0.12 and 1 μg ml^-1 without significant interference from other recombinant proteins. The analytical imprecision (CV%) and accuracy of this Ag85B protein biosensor were 9.73-10.99% and 95.29%, respectively. In addition, an irrelevant antibody and other recombinant proteins were employed as a negative control to demonstrate the non-specific interaction of the antigen and antibody. The success of this immunosensor system for Ag85B protein detection facilitates the construction of a promising device which can shorten the turnaround time for the diagnosis of tuberculosis compared to a standard culture method. Furthermore, this device could also be applied for real-time growth monitoring of Mycobacterium tuberculosis in a mycobacterial culture system.

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

PURPOSE

Combining the results of presumptive cord formation in smear and MPT64 Antigen Immunochromatographic Assay has been suggested to reduce the false negative and positive rates for identification of Mycobacterium tuberculosis (MTB) complex in liquid culture. This study was done to evaluate the clinical utility of combining the results of the two tests for rapid identification MTB complex in mycobacterial isolates.

METHODS

484 isolates of mycobacteria obtained in MGIT culture were identified using presumptive cord formation in smear and further by MPT64 Antigen ICT assay. Result obtained were analyzed taking PNB inhibition test as the reference standard.

RESULTS

Combining the results of the two tests, 464 (95.9%) isolates were correctly identified while discrepant results were obtained in 20 (4.1%) isolates. When the results of the two tests were intersected, the specificity and PPV was 100%, but the sensitivity decreased to 96.4% and the NPV to 68.6%. On the other hand, when the results of the two methods were combined, the sensitivity and NPV was 100%, but the specificity decreased to 88.6% and the PPV to 99.1%.

CONCLUSION

Presumptive cord formation and MPT64 antigen ICT assay can be used in combination for identification of MTB complex. When both the test are positive, the culture can be reported to contain MTB complex. If both the tests are negative, the culture should be reported to contain NTM. Only when discrepant results are obtained by the two tests, further evaluation is necessary to ensure an accurate diagnosis.

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

With detonation nanodiamonds (DNDs) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS), we previously identified early secreted cell filtrate protein 10 (CFP-10) as a candidate Mycobacterium tuberculosis complex (MTC) biomarker. The performance of the CFP-10 biomarker was initially evaluated in relatively small mycobacterial samples (n = 42 samples) in our previous study. In this study, we conducted DND MALDI-TOF MS experiments to investigate the specificity and sensitivity of the MTC biomarker with 312 MTC and 52 nontuberculous mycobacteria (NTM) clinical samples. The frequency and intensity of the acquired CFP-10 mass-to-charge (m/z) peaks were checked with a program to validate that the singly and doubly charged CFP-10 antigen can be treated as a MTC biomarker. We confirmed that by detecting the singly charged species of CFP-10 antigen, the sensitivity and the specificity of MTC samples could reach 97.4% and 100% and no CFP-10 biomarker could be found in NTM samples. This indicates with CFP-10 biomarker it is easy to distinguish MTC from NTM. Besides, the observed intensity ratio of singly and doubly charged species of CFP-10 antigen was 3.3 ± 2.6 and the CFP-10 antigen could maintain good signal intensity for a week. Our results suggest that, with the DND MALDI-TOF mass spectrometry approach, CFP-10 antigen can be used as an early diagnosis biomarker in clinical practice.

Direct detection and identification of acid-fast bacteria from smear-positive broth cultures using a pyrosequencing method

Broth culture is a standard method for detection of acid-fast bacteria (AFB) (e.g., Mycobacterium and Nocardia) from patient specimens. Direct nucleic acid-based identification from smear-positive broths expedites the infectious disease diagnosis. We developed and evaluated the performance of a pyrogram-based technique (direct-broth-pyrosequencing [DBP]) to identify AFB directly from smear-positive broths. One hundred thirteen AFB-positive broths from patient specimens were tested. Bacterial DNA was amplified by polymerase chain reaction and sequenced using the PyroMark ID system. The DBP method correctly identified the AFB species/group in 109 (97%) of the 113 broths, including 15 Mycobacterium species and 4 Nocardia species. Three broths that yielded indeterminate results were found to be AFB-AFB mixed broths and required purified colonies on solid media for definite identification. The 4th broth was repeatedly identified by sequencing to be Mycobacterium intracellulare, even though the organism was not isolated and the AccuProbe was negative. This method did not identify the AFB organisms from broths containing 2 AFB organisms, but did not produce false identification. No cross-reaction was observed when AFB-positive broths were spiked with non-AFB microorganisms, indicating that the DBP method was specific to AFB. The DBP method gives rapid (within 8 h), accurate AFB identification directly from broth cultures and provides another useful AFB identification tool in a clinical laboratory.

Mycobacterium tuberculosis pili (MTP), a putative biomarker for a tuberculosis diagnostic test

Novel biomarkers are urgently needed for point of care TB diagnostics. In this study, we investigated the potential of the pilin subunit protein encoded by the mtp gene as a diagnostic biomarker. BLAST analysis of the mtp gene on published genome databases, and amplicon sequencing were performed in Mycobacterium tuberculosis Complex (MTBC) strains and other organisms. The protein secondary structure of the amino acid sequences of non-tuberculous Mycobacteria that partially aligned with the mtp sequence was analysed with PredictProtein software. The mtp gene and corresponding amino acid sequence of MTBC were 100% homologous with H37Rv, in contrast to the partial alignment of the non-tuberculous Mycobacteria. The mtp gene was present in all 91 clinical isolates of MTBC. Except for 2 strains with point mutations, the sequence was 100% conserved among the clinical strains. The mtp gene could not be amplified in all non-tuberculous Mycobacteria and respiratory organisms. The predicted MTP protein structure of Mycobacterium avium, Mycobacterium ulcerans and Mycobacterium abscessus differed significantly from that of the M. tuberculosis, which was similar to Mycobacterium marinum. The absence of the mtp gene in non-tuberculous Mycobacteria and other respiratory bacteria suggests that its encoded product, the pilin subunit protein of M. tuberculosis may be a suitable marker for a point of care TB test.

The application of anti-ESAT-6 monoclonal antibody fluorescent probe in ex vivo near-infrared fluorescence imaging in mice with pulmonary tuberculosis

Here, we aimed to assess the feasibility of anti-ESAT-6 monoclonal antibody (mAb) coupling with IR783 and rhodamine fluorescent probe in the detection of ESAT-6 expression in tuberculosis tissue of mice using near-infrared fluorescence imaging. IR783 and rhodamine were conjugated to the anti-ESAT-6 mAb or IgG. Mice in the experimental group were injected with fluorescence-labeled mAb probe, and mice in the control group were injected with fluorescence-labeled non-specific IgG antibody. Twenty-four hours later, the lung tissue of mice was examined using ex vivo near-infrared fluorescence imaging. In addition, the contrast-to-noise ratio (CNR) was calculated by measuring the signal intensities of the pulmonary lesions, normal lung tissue and background noise. The frozen lung tissue section was examined under fluorescence microscopy and compared with hemoxylin and eosin (HE) staining. The ex vivo near-infrared fluorescence imaging showed that the fluorescence signal in the lung tuberculosis lesions in the experimental group was significantly enhanced, whereas there was only a weak fluorescence signal or even no fluorescence signal in the control group. CNR values were 64.40 ± 7.02 (n = 6) and 8.75 ± 3.87 (n = 6), respectively (t = 17.01, p < 0.001). The fluorescence accumulation distribution detected under fluorescence microscopy was consistent with HE staining of the tuberculosis region. In conclusion, anti-ESAT-6 mAb fluorescent probe could target and be applied in specific ex vivo imaging of mice tuberculosis, and may be of further use in tuberculosis in living mice.

Tuberculosis diagnosis using immunodominant, secreted antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major public health concern in most low-income countries. Hence, rapid and sensitive TB diagnostics play an important role in detecting and preventing the disease. In addition to established diagnostic methods, several new approaches have been reported. Some techniques are simple but time-consuming, while others require complex instrumentation. One prominent and readily available approach is to detect proteins that Mycobacterium tuberculosis secretes, such as Mpt64, the 6-kDa early secreted antigenic target (Esat6), the 10-kDa culture filtrate protein (Cfp10), and the antigen 85 (Ag85) complex. Although their functions are not fully understood, a growing body of molecular evidence implicates them in M. tuberculosis virulence. Currently these biomarkers are either being used or investigated for use in skin patch tests, biosensor analyses, and immunochromatographic, immunohistochemical, polymerase chain reaction-based, and enzyme-linked immunosorbent assays. This review provides a comprehensive discussion of the roles these immunodominant antigens play in M. tuberculosis pathogenesis and compares diagnostic methods based on the detection of these proteins with more established tests for TB.

Rapid identification and drug susceptibility screening of ESAT-6 secreting Mycobacteria by a NanoELIwell assay

To meet the global needs of tuberculosis (TB) control, a nanoELIwell device was developed as a multifunctional assay for TB diagnosis and drug susceptibility testing. The device integrates on-chip culturing of mycobacteria, immunoassay, and high-resolution fluorescent imaging. Mycobacterium smegmatis and Mycobacterium kansasii were used as models of Mycobacterium tuberculosis to evaluate device integrity by using antigens, Ag85 and ESAT-6, as biomarkers. As a result, the nanoELIwell device detected antigens released from a single bacterium within 24–48-hour culture. Antimycobacterial drug-treated M. smegmatis showed significant decreased in Ag85 antigen production when treated with ethambutol and no change in antigen production when treated with rifampin, demonstrating drug susceptibility and resistance, respectively. The nanoELIwell assay also distinguished the ESAT-6-secreting M. kansasii from the non-ESAT-6-secreting M. simiae. The combination of microwell technology and ELISA assay holds potential to the development of a rapid, sensitive, and specific diagnostics and susceptibility testing of TB.

Evaluation of in-house PCR for diagnosis of smear-negative pulmonary tuberculosis in Kampala, Uganda

Background

Nucleic acid amplification tests (NAATs) have offered hope for rapid diagnosis of tuberculosis (TB). However, their efficiency with smear-negative samples has not been widely studied in low income settings. Here, we evaluated in-house PCR assay for diagnosis of smear-negative TB using Lowenstein-Jensen (LJ) culture as the baseline test. Two hundred and five pulmonary TB (PTB) suspects with smear-negative sputum samples, admitted on a short stay emergency ward at Mulago Hospital in Kampala, Uganda, were enrolled. Two smear-negative sputum samples were obtained from each PTB suspect and processed simultaneously for identification of MTBC using in-house PCR and LJ culture.

Results

Seventy two PTB suspects (35%, 72/205) were LJ culture positive while 128 (62.4%, 128/205) were PCR-positive. The sensitivity and specificity of in-house PCR for diagnosis of smear-negative PTB were 75% (95% CI 62.6-85.0) and 35.9% (95% CI 27.2-45.3), respectively. The positive and negative predictive values were 39% (95% CI 30.4-48.2) and 72.4% (95% CI 59.1-83.3), respectively, while the positive and negative likelihood ratios were 1.17 (95% CI 0.96-1.42) and 0.70 (95% CI 0.43-1.14), respectively. One hundred and seventeen LJ culture-negative suspects (75 PCR-positive and 42 PCR-negative) were enrolled for follow-up at 2 months. Of the PCR-positive suspects, 45 (60%, 45/75) were still alive, of whom 29 (64.4%, 29/45) returned for the follow-up visit; 15 (20%, 15/75) suspects died while another 15 (20%, 15/75) were lost to follow-up. Of the 42 PCR-negative suspects, 22 (52.4%, 22/42) were still alive, of whom 16 (72.7%, 16/22) returned for follow-up; 11 (26.2%, 11/42) died while nine (21.4%, 9/42) were lost to follow-up. Overall, more PCR-positive suspects were diagnosed with PTB during follow-up visits but the difference was not statistically significant (27.6%, 8/29 vs. 25%, 4/16, p = 0.9239). Furthermore, mortality was higher for the PCR-negative suspects but the difference was also not statistically significant (26.2% vs. 20% p = 0.7094).

Conclusion

In-house PCR correlates poorly with LJ culture for diagnosis of smear-negative PTB. Therefore, in-house PCR may not be adopted as an alternative to LJ culture.

Detonation nanodiamonds for rapid detection of clinical isolates of Mycobacterium tuberculosis complex in broth culture media

Routinely used molecular diagnostic methods for mycobacterium identification are expensive and time-consuming. To tackle this problem, we develop a method to streamline identification of Mycobacterium tuberculosis complex (MTBC) in broth culture media by using detonation nanodiamonds (DNDs) as a platform to effectively capture the antigen secreted by MTBC which is cultured in BACTEC MGIT 960, followed by the analysis of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). The 5 nm DNDs can capture the MTBC secretory antigen without albumin interference. With on diamond digestion, we confirm the DND captured antigen is cell filtrate protein 10 (CFP-10) because its Mascot analysis shows a score of 68. The dot blotting method further verifies a positive reaction with anti-CFP-10, indicating that CFP-10 is secreted in the medium of mycobacterium growth indicator tube (MGIT) and captured by DNDs. The minimal CFP-10 protein detection limit was 0.09 μg/mL. Furthermore, our approach can avoid the false-positive identification of MTBC by immunological methods due to cross-reactivity. Five hundred consecutive clinical specimens subjected to routine mycobacteria identification in hospital were used in this study, and the sensitivity of our method is 100% and the specificity is 98%. The analysis of each MTBC sample from culture solution can be finished within 1 h and thus shortens the turnaround time of MTBC identification of gold standard culture methods. In sum, DND MALDI-TOF MS for the detection of MTBC is rapid, specific, safe, reliable, and inexpensive.

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)

Ocular tuberculosis is difficult to diagnose but should be suspected when uveitis fails to respond to inflammation suppressive therapy. Interferon-gamma release assays (IGRAs) represent a substantial help to diagnose suspected ocular tuberculosis especially in non-endemic areas. Indocyanine green angiography (ICGA) is able to detect clinically silent choroiditis that, when associated with a positive IGRA test, should lead the clinician to suspect ocular tuberculosis, warranting specific therapy. The fact that IGRA tests can also react with some atypical strains of mycobacteria is not always known. We report here a case with resistant post-operative inflammation that presented with occult ICGA-detected choroiditis and a positive IGRA test that was most probably due to the non-tuberculous mycobacterium (NTM) Mycobacterium kansasii. A 66 year-old man presented with a resistant cystoid macular oedema (CMO) in his left eye after combined cataract and epiretinal membrane surgery. At entry, his best-corrected visual acuity (BCVA) was 0.5 for far and near OS. Intraocular inflammation measured by laser flare photometry was elevated in the left eye (54.4 ph/ms) and also in the right eye (50.9 ph/ms). Four subTenon's injections of 40 mg of triamcinolone did not produce any substantial improvement. Therefore a complete uveitis work-up was performed. Fluorescein angiography showed CMO OS and ICGA showed numerous hypofluorescent dots and fuzziness of choroidal vessels in both eyes. Among performed laboratory tests, the QuantiFERON®-TB Gold test was positive. After a pulmonological examination disclosing a right upper lobe infiltrate, the patient was started on a triple anti-tuberculous therapy. Bronchial aspirate, obtained during bronchoscopy, was Ziehl-positive and culture grew M. kansasii. Nine months later, BCVA OS increased to 1.0 and flare decreased to 40.2 ph/ms. The CMO OS resolved angiographically and did not recur with a macula still slightly thickened on OCT. Suspected ocular tuberculosis based on clinical findings and a positive IGRA test can, in rare instances, be due to atypical mycobacteria that also produce positive IGRA tests such as M. kansasii, M. szulgai, M. gordonae, M. flavescens and M. marinum. In our case failure to isolate the atypical mycobacterium would not have had negative therapeutic consequences, as M. kansasii is sensitive to the standard anti-tuberculous treatments, which is not the case with other NTMs.

Evaluation of Capilia TB assay for rapid identification of Mycobacterium tuberculosis complex in BACTEC MGIT 960 and BACTEC 9120 blood cultures

Background

Capilia TB is a simple immunochromatographic assay based on the detection of MPB64 antigen specifically secreted by the Mycobacterium tuberculosis complex (MTC). Capilia TB was evaluated for rapid identification of MTC from BACTEC MGIT 960 and BACTEC 9120 systems in Kampala, Uganda. Since most studies have mainly dealt with respiratory samples, the performance of Capilia TB on blood culture samples was also evaluated.

Methods

One thousand samples from pulmonary and disseminated tuberculosis (TB) suspects admitted to the JCRC clinic and the TB wards at Old Mulago hospital in Kampala, Uganda, were cultured in automated BACTEC MGIT 960 and BACTEC 9120 blood culture systems. BACTEC-positive samples were screened for purity by sub-culturing on blood agar plates. Two hundred and fifty three (253) samples with Acid fast bacilli (AFB, 174 BACTEC MGIT 960 and 79 BACTEC 9120 blood cultures) were analyzed for presence of MTC using Capilia TB and in-house PCR assays.

Results

The overall Sensitivity, Specificity, Positive and Negative Predictive values, and Kappa statistic for Capilia TB assay for identification of MTC were 98.4%, 97.6%, 97.7%, 98.4% and 0.96, respectively. Initially, the performance of in-house PCR on BACTEC 9120 blood cultures was poor (Sensitivity, Specificity, PPV, NPV and Kappa statistic of 100%, 29.3%,7%, 100% and 0.04, respectively) but improved upon sub-culturing on solid medium (Middlebrook 7H10) to 100%, 95.6%, 98.2%, 100% and 0.98, respectively. In contrast, the Sensitivity and Specificity of Capilia TB assay was 98.4% and 97.9%, respectively, both with BACTEC blood cultures and Middlebrook 7H10 cultured samples, revealing that Capilia was better than in-house PCR for identification of MTC in blood cultures. Additionally, Capilia TB was cheaper than in-house PCR for individual samples ($2.03 vs. $12.59, respectively), and was easier to perform with a shorter turnaround time (20 min vs. 480 min, respectively).

Conclusion

Capilia TB assay is faster and cheaper than in-house PCR for rapid identification of MTC from BACTEC MGIT 960 and BACTEC 9120 culture systems in real-time testing of AFB positive cultures.