Predicting the outcome of therapy for pulmonary tuberculosis

New Insights into Biomarkers for Evaluating Therapy Efficacy in Pulmonary Tuberculosis: A Narrative Review

Evaluating therapy efficacy is crucial for patients with tuberculosis (TB), especially those with drug-resistant tuberculosis (DR-TB). The World Health Organization currently recommends sputum smear and culture as the standard methods for evaluating pulmonary tuberculosis (PTB) therapy efficacy. However, these approaches have limitations including low sensitivity, lengthy culture periods, and susceptibility to contamination. There is an urgent need for dependable biomarkers to evaluate therapy efficacy in patients with PTB. Numerous new biomarkers of Mycobacterium tuberculosis (MTB) and the host have been used in recent studies to evaluate PTB therapy efficacy. A systematic review and update of these biomarkers can facilitate the discovery of novel biomarkers and assessment models, as well as provide a solid scientific basis for alternative indicators of evaluating therapy efficacy. In this review we summarize the recent advancements and limitations of biomarkers used to monitor therapy efficacy, highlighting the importance of utilizing a combination of biomarkers. Although some biomarkers have potential in evaluating the efficacy of therapy in patients with PTB, they also have some limitations. Further research, validation, and optimization are required to identify the most reliable and effective alternative biomarkers and apply them to clinical practice.

Increased Neutrophil Count and Decreased Neutrophil CD15 Expression Correlate With TB Disease Severity and Treatment Response Irrespective of HIV Co-infection

Tuberculosis remains a leading cause of death globally despite curative treatment, partly due to the difficulty of identifying patients who will not respond to therapy. Simple host biomarkers that correlate with response to drug treatment would facilitate improvement in outcomes and the evaluation of novel therapies. In a prospective longitudinal cohort study, we evaluated neutrophil count and phenotype at baseline, as well as during TB treatment in 79 patients [50 (63%) HIV-positive] with microbiologically confirmed drug susceptible TB undergoing standard treatment. At time of diagnosis, blood neutrophils were highly expanded and surface expression of the neutrophil marker CD15 greatly reduced compared to controls. Both measures changed rapidly with the commencement of drug treatment and returned to levels seen in healthy control by treatment completion. Additionally, at the time of diagnosis, high neutrophil count, and low CD15 expression was associated with higher sputum bacterial load and more severe lung damage on chest x-ray, two clinically relevant markers of disease severity. Furthermore, CD15 expression level at diagnosis was associated with TB culture conversion after 2 months of therapy (OR: 0.14, 95% CI: 0.02, 0.89), a standard measure of early TB treatment success. Importantly, our data was not significantly impacted by HIV co-infection. These data suggest that blood neutrophil metrics could potentially be exploited to develop a simple and rapid test to help determine TB disease severity, monitor drug treatment response, and identify subjects at diagnosis who may respond poorly to treatment.

Screening and identification of potential protein biomarkers for evaluating the efficacy of intensive therapy in pulmonary tuberculosis

This research aimed to discover potential biomarkers for evaluating the therapeutic efficacy of intensive therapy in pulmonary tuberculosis (TB). Protein profiles in 2-months intensively treated TB patients, untreated TB patients, and healthy controls were investigated with iTRAQ-2DLC-MS/MS technique. 71 differential proteins were identified in 2-months intensively treated TB patients. Significant differences in complement component C7 (CO7), apolipoprotein A-IV (APOA4), apolipoprotein C-II (APOC2), and angiotensinogen (ANGT) were found by ELISA validation. CO7 and ANGT were also found significantly different in sputum negative patients, compared with sputum positive patients after intensive treatment. Clinical analysis showed that after 2-months intensive treatment several indicators were significantly changed, and the one-year cure rate of sputum negative patients were significantly higher than sputum positive patients. Diagnostic models consisting of APOC2, CO7 and APOA4 were established to distinguish intensively treated TB patients from untreated TB patients and healthy controls with the AUC value of 0.910 and 0.935. Meanwhile, ANGT and CO7 were combined to identify sputum negative and sputum positive TB patients after intensive treatment with 89.36% sensitivity, 71.43% specificity, and the AUC value of 0.853. The results showed that APOC2, CO7, APOA4, and ANGT may be potential biomarkers for evaluating the efficacy of intensive anti-TB therapy.

Comparing efficacies of moxifloxacin, levofloxacin and gatifloxacin in tuberculosis granulomas using a multi-scale systems pharmacology approach

Granulomas are complex lung lesions that are the hallmark of tuberculosis (TB). Understanding antibiotic dynamics within lung granulomas will be vital to improving and shortening the long course of TB treatment. Three fluoroquinolones (FQs) are commonly prescribed as part of multi-drug resistant TB therapy: moxifloxacin (MXF), levofloxacin (LVX) or gatifloxacin (GFX). To date, insufficient data are available to support selection of one FQ over another, or to show that these drugs are clinically equivalent. To predict the efficacy of MXF, LVX and GFX at a single granuloma level, we integrate computational modeling with experimental datasets into a single mechanistic framework, GranSim. GranSim is a hybrid agent-based computational model that simulates granuloma formation and function, FQ plasma and tissue pharmacokinetics and pharmacodynamics and is based on extensive in vitro and in vivo data. We treat in silico granulomas with recommended daily doses of each FQ and compare efficacy by multiple metrics: bacterial load, sterilization rates, early bactericidal activity and efficacy under non-compliance and treatment interruption. GranSim reproduces in vivo plasma pharmacokinetics, spatial and temporal tissue pharmacokinetics and in vitro pharmacodynamics of these FQs. We predict that MXF kills intracellular bacteria more quickly than LVX and GFX due in part to a higher cellular accumulation ratio. We also show that all three FQs struggle to sterilize non-replicating bacteria residing in caseum. This is due to modest drug concentrations inside caseum and high inhibitory concentrations for this bacterial subpopulation. MXF and LVX have higher granuloma sterilization rates compared to GFX; and MXF performs better in a simulated non-compliance or treatment interruption scenario. We conclude that MXF has a small but potentially clinically significant advantage over LVX, as well as LVX over GFX. We illustrate how a systems pharmacology approach combining experimental and computational methods can guide antibiotic selection for TB.

Tuberculosis (TB) is caused by infection with the bacterium Mycobacterium tuberculosis (Mtb) and kills 1.5 million people each year. TB requires at least 6 months of treatment with up to four drugs, and is characterized by formation of granulomas in patient lungs. Granulomas are spherical collections of host cells and bacteria. Fluoroquinolones (FQs) are a class of drug that could help shorten TB treatment. Three FQs that are used to treat TB are: moxifloxacin (MXF), levofloxacin (LVX) or gatifloxacin (GFX). To date, it is unclear if one FQ is better than the others at treating TB, in part because little is known about how these drugs distribute and work inside the lung granulomas. We use computer simulations of Mtb infection and FQ treatment within granulomas to predict which FQ is better and why. Our computer model is calibrated to multiple experimental data sets. We compare the three FQs by multiple metrics, and predict that MXF is better than LVX and GFX because it kills bacteria more quickly, and it works better when patients miss doses. However, all three FQs are unable to kill a part of the bacterial population living in the center of granulomas. Our results can now inform future experimental studies.

Early interventions for diabetes related tuberculosis associate with hastened sputum microbiological clearance in Virginia, USA

Background

Diabetes complicates tuberculosis (TB) treatment including a prolonged time of sputum culture conversion to negative growth. Since 2013 in Virginia, interventions early in the treatment course have used therapeutic drug monitoring and dose correction for isoniazid and rifampin after 2 weeks of TB treatment in patients with diabetes along with nurse manager initiated diabetes education and linkage to care.

Methods

A retrospective cohort study of the state TB registry was performed for patients initiating drug-susceptible pulmonary TB treatment that were matched for age, gender, chest imaging and sputum smear status to compare time to sputum culture conversion and other clinical outcomes in the pre-and post-intervention groups.

Results

Three hundred sixty-three patients had documented time to sputum culture conversion in the pre-and post-intervention periods, including 56 (15%) with diabetes. Seventy-four (57%) of all patients with diabetes were ≥60 years of age at treatment initiation. Twenty-six patients with diabetes were matched in each group. Mean time to sputum culture conversion in the post-intervention group was 42 ± 22 days compared to the pre-intervention group of 62 ± 31 days (p = 0.01). In the post-intervention group 21 (80%) of patients with diabetes had culture conversion by 2 months compared to 13 (50%) in the pre-intervention group (p = 0.04).

Conclusions

Early interventions for diabetes related TB in the programmatic setting may hasten sputum culture conversion.

Comparative Proteomics of Activated THP-1 Cells Infected with Mycobacterium tuberculosis Identifies Putative Clearance Biomarkers for Tuberculosis Treatment

Biomarkers for determining clearance of Mycobacterium tuberculosis (Mtb) infection during anti-tuberculosis therapy or following exposure could facilitate enhanced monitoring and treatment. We screened for biomarkers indicating clearance of Mtb infection in vitro. A comparative proteomic analysis was performed using GeLC MSI/MS. Intracellular and secreted proteomes from activated THP-1 cells infected with the Mtb H37Rv strain (MOI = 1) and treated with isoniazid and rifampicin for 1 day (infection stage) and 5 days (clearance stage) were analyzed. Host proteins associated with early infection (n = 82), clearance (n = 121), sustained in both conditions (n = 34) and suppressed by infection (n = 46) were elucidated. Of the potential clearance markers, SSFA2 and CAECAM18 showed the highest and lowest protein intensities, respectively. A western blot of CAECAM18 validated the LC MS/MS result. For three clearance markers (SSFA2, PARP14 and PSME4), in vivo clinical validation was concordantly reported in previous patient cohorts. A network analysis revealed that clearance markers were enriched amongst four protein interaction networks centered on: (i) CD44/CCND1, (ii) IFN-β1/NF-κB, (iii) TP53/TGF-β and (iv) IFN-γ/CCL2. After infection, proteins associated with proliferation, and recruitment of immune cells appeared to be enriched possibly reflecting recruitment of defense mechanisms. Counteracting proteins (CASP3 vs. Akt and NF-κB vs. TP53) associated with apoptosis regulation and its networks were enriched among the early and sustained infection biomarkers, indicating host-pathogen competition. The BRCA1/2 network was suppressed during infection, suggesting that cell proliferation suppression is a feature of Mtb survival. Our study provides insights into the mechanisms of host-Mtb interaction by comparing the stages of infection clearance. The identified clearance biomarkers may be useful in monitoring tuberculosis treatment.

Improving the tuberculosis drug development pipeline

Mycobacterium tuberculosis is considered one of the most successful pathogens and multidrug-resistant tuberculosis, a disease that urgently requires new chemical entities to be developed for treatment. There are currently several new molecules under clinical investigation in the tuberculosis (TB) drug development pipeline. However, the complex lifestyle of M. tuberculosis within the host presents a barrier to the development of new drugs. In this review, we highlight the reasons that make TB drug discovery and development challenging as well as providing solutions, future directions and alternative approaches to new therapeutics for TB.

Assessment of the sensitivity and specificity of Xpert MTB/RIF assay as an early sputum biomarker of response to tuberculosis treatment

BACKGROUND

An accurate biomarker is urgently needed to monitor the response to treatment in patients with pulmonary tuberculosis. The Xpert MTB/RIF assay is a commercially available real-time PCR that can be used to detect Mycobacterium-tuberculosis-specific DNA sequences in sputum samples. We therefore evaluated this assay with serial sputum samples obtained over 26 weeks from patients undergoing treatment for tuberculosis.

METHODS

We analysed sputum samples from 221 patients with smear-positive tuberculosis enrolled at two sites (Cape Town, South Africa, and Mbeya, Tanzania) of a multicentre randomised clinical trial REMoxTB of antituberculosis treatment on a weekly basis (weeks 0 to 8), then at weeks 12, 17, 22, and 26 after treatment initiation. The Xpert MTB/RIF results over time were compared with the results of standard smear microscopy and culture methods.

FINDINGS

We obtained and analysed 2741 sputum samples from 221 patients. The reduction in positivity rates with Xpert MTB/RIF were slower than those with the standard methods. At week 8, positive results were obtained for 62 (29%) of 212 sputum samples with smear microscopy, 46 (26%) of 175 with solid culture (Löwenstein-Jensen medium), 77 (42%) of 183 with liquid culture (Bactec MGIT960 system), and 174 (84%) of 207 with Xpert MTB/RIF; at 26 weeks, positive results were obtained for ten (5%) of 199, four (3%) of 157, seven (4%) of 169, and 22 (27%) of 83 sputum samples, respectively. The reduction in detection of quantitative M tuberculosis DNA with Xpert MTB/RIF correlated with smear grades (ρ=-0·74; p<0·0001), solid culture grades (ρ=-0·73; p<0·0001), and time to liquid culture positivity (ρ=0·73; p<0·0001). Compared with the combined binary smear and culture results as a reference standard, the Xpert MTB/RIF assay had high sensitivity (97·0%, 95% CI 95·8-97·9), but poor specificity (48·6%, 45·0-52·2).

INTERPRETATION

The poor specificity precludes the use of the Xpert MTB/RIF assay as a biomarker for monitoring tuberculosis treatment, and should not replace standard smear microscopy and culture.

FUNDING

Global Alliance for TB Drug Development, Bill & Melinda Gates Foundation, UK Medical Research Council, German Ministry of Science and Technology.

Radiologic Responses in Cynomolgus Macaques for Assessing Tuberculosis Chemotherapy Regimens

Trials to test new drugs currently in development against tuberculosis in humans are impractical. All animal models to prioritize new regimens are imperfect, but nonhuman primates (NHPs) infected with Mycobacterium tuberculosis develop active tuberculosis (TB) disease with a full spectrum of lesion types seen in humans. Serial 2-deoxy-2-[¹⁸F]-fluoro-d-glucose (FDG) positron emission tomography (PET) with computed tomography (CT) imaging was performed on cynomolgus macaques during infection and chemotherapy with individual agents or the four-drug combination therapy most widely used globally. The size and metabolic activity of lung granulomas varied among animals and even within a single animal during development of disease. Individual granulomas within untreated animals had highly local and independent outcomes, some progressing in size and FDG uptake, while others waned, illustrating the highly dynamic nature of active TB. At necropsy, even untreated animals were found to have a proportion of sterile lesions consistent with the dynamics of this infection. A more marked reduction in overall metabolic activity in the lungs (decreased FDG uptake) was associated with effective treatment. A reduction in the size of individual lesions correlated with a lower bacterial burden at necropsy. Isoniazid treatment was associated with a transient increase in metabolic activity in individual lesions, whereas a net reduction occurred in most lesions from rifampin-treated animals. Quadruple-drug therapy resulted in the highest decrease in FDG uptake. The findings of PET-CT imaging may provide an important early correlate of the efficacy of novel combinations of new drugs that can be directly translated to human clinical trials.

Time to detection of Mycobacterium tuberculosis as an alternative to quantitative cultures

Testing new drugs is critical to improving the treatment of tuberculosis. Quantitative cultures of Mycobacterium tuberculosis on solid media have been used in Phase 1 and 2 trials, but are time and resource intensive. Time to detection (TTD) of growth of M. tuberculosis in automated liquid culture systems is an alternative. TTD has been shown to correlate with CFU in quantitative cultures, and is faster and simpler to perform. We compared TTD in the BACTEC 460 liquid culture system with CFU in a clinical trial that included 110 subjects. Comparing all sputum cultures collected between baseline and 2 months we found a strong negative correlation between log(10) CFU and TTD (rho = -0.91). In addition, when TTD at baseline was compared with 1 and 2 month sputum culture positivity, subjects whose cultures were negative after 1 and 2 months had a significantly longer median baseline TTD compared with subjects whose cultures were positive at 1 and 2 months (5 vs. 3 days and 3 vs. 2 days, respectively). TTD compares closely with CFU and represents a faster, simpler alternative to quantitative cultures.

Biomarkers and diagnostics for tuberculosis: progress, needs, and translation into practice

Human infection with Mycobacterium tuberculosis can progress to active disease, be contained as latent infection, or be eradicated by the host response. Tuberculosis diagnostics classify a patient into one of these categories. These are not fixed distinct states, but rather are continua along which patients can move, and are affected by HIV infection, immunosuppressive therapies, antituberculosis treatments, and other poorly understood factors. Tuberculosis biomarkers-host or pathogen-specific-provide prognostic information, either for individual patients or study cohorts, about these outcomes. Tuberculosis case detection remains difficult, partly because of inaccurate diagnostic methods. Investments have yielded some progress in development of new diagnostics, although the existing pipeline is limited for tests for sputum-smear-negative cases, childhood tuberculosis, and accurate prediction of reactivation of latent tuberculosis. Despite new, sensitive, automated molecular platforms for detection of tuberculosis and drug resistance, a simple, inexpensive point-of-care test is still not available. The effect of any new tests will depend on the method and extent of their introduction, the strength of the laboratories, and the degree to which access to appropriate therapy follows access to diagnosis. Translation of scientific progress in biomarkers and diagnostics into clinical and public health programmes is possible-with political commitment, increased funding, and engagement of all stakeholders.

Rate and amplification of drug resistance among previously-treated patients with tuberculosis in Kampala, Uganda

BACKGROUND

Drug-resistant Mycobacterium tuberculosis has emerged as a global threat. In resource-constrained settings, patients with a history of tuberculosis (TB) treatment may have drug-resistant disease and may experience poor outcomes. There is a need to measure the extent of and risk factors for drug resistance in such patients.

METHODS

From July 2003 through November 2006, we enrolled 410 previously treated patients with TB in Kampala, Uganda. We measured the prevalence of resistance to first- and second-line drugs and analyzed risk factors associated with baseline and acquired drug resistance.

RESULTS

The prevalence of multidrug-resistant TB was 12.7% (95% confidence interval [95% CI], 9.6%-16.3%). Resistance to second-line drugs was low. Factors associated with multidrug-resistant TB at enrollment included a history of treatment failure (odds ratio, 23.6; 95% CI, 7.7-72.4), multiple previous TB episodes (odds ratio, 15.6; 95% CI, 5.0-49.1), and cavities present on chest radiograph (odds ratio, 5.9; 95% CI, 1.2-29.5). Among a cohort of 250 patients, 5.2% (95% CI, 2.8%-8.7%) were infected with M. tuberculosis that developed additional drug resistance. Amplification of drug resistance was associated with existing drug resistance at baseline (P < .01) and delayed sputum culture conversion (P < .01).

CONCLUSIONS

The burden of drug resistance in previously treated patients with TB in Uganda is sizeable, and the risk of generating additional drug resistance is significant. There is an urgent need to improve the treatment for such patients in low-income countries.

Prediction of delayed treatment response in pulmonary tuberculosis: use of time to positivity values of Bactec cultures

New drugs that can shorten tuberculosis (TB) treatment and target drug resistant strains are urgently needed. A test which could predict patients at risk of a delayed response to treatment would facilitate clinical trials of new anti-tuberculosis drugs. A widely-used test for the assessment of response to treatment is sputum smear examination. Patients who are smear positive after 2 and 3 months of treatment are said to have delayed and significantly delayed treatment responses respectively. Time to positivity (TTP) values of Bactec cultures, from the first 2 weeks of treatment were used to predict delayed and significantly delayed treatment responses in patients with first time pulmonary tuberculosis. Changes in TTP values early in treatment were transformed to a response ratio (r). Values of r that were less than a threshold value (r(c)) indicated patients who were at risk of having delayed or significantly delayed response to treatment. Accuracy of prediction was sensitive to the timing of sputum sampling and adherence to therapy in the first 2 weeks. Based on TTP data from the first 2 weeks of treatment, significantly delayed treatment response could be predicted with a sensitivity of 75% and a specificity of 62% while the positive (PPV) and negative predictive values (NPV) were 14% and 97% respectively. While the high NPV indicates that a large proportion of patients with a satisfactory response to treatment can be reliably identified, the low PPV value underlines the need to use TTP in conjunction with other markers of disease activity to predict unfavourable treatment response in tuberculosis treatment.

[Tobacco smoking and sputum smear conversion in pulmonary tuberculosis]

BACKGROUND AND OBJECTIVE

To analyze if cigarette smoking delays the sputum smear conversion in pulmonary tuberculosis.

PATIENTS AND METHOD

Ninety eight patients were diagnosed with pulmonary tuberculosis. Patients were all not immunosuppressed, infected by human immunodeficiecy virus (HIV) or drug resistant. Sixty four of them were smokers with a pack-year index (standard deviation) of 33.69 (23.12). Delayed sputum smear conversion (DC) was considered when 2 positive sputum culture results were obtained in the second month of anti-tuberculous treatment and was associated with the following variables in 2 groups: a) total group (in which all the patients were included): age, sex, smoking habits, risk factors (alcohol consumption, diabetes mellitus, immunosuppression, drug addicion, malnutrition), time with symptoms, radiologic presentation and bacterial load, and b) smokers: age, sex, risk factors, time with symptoms, radiologic presentation, bacterial load and pack-year index. For the statistical analysis, chi2 test, Student t test and logistic regression model were used, considering the dependant variable DC.

RESULTS

In the total group, 17 patients (17.3%) had DC, 16 of them had a history of smoking and in the univariate analysis it was associated with: alcohol consumption, time with symptoms, radiologic presentation as bilateral cavitary infiltrates and smoking habits. The logistic regression analysis showed an association with smoking habits (odds ratio = 9.8; p = 0.03) and bilateral cavitary infiltrates (odds ratio = 3.61; p = 0.02). In the group of smokers, DC was associated in the univariate analysis with the female sex.

CONCLUSIONS

Smoking habits delay sputum conversion in patients with pulmonary tuberculosis not associated with HIV and non-resistant bacilli. According to these results it is necessary to assist smoking cessation in patients who are receiving antituberculous treatment.

Biomarkers of treatment response in clinical trials of novel antituberculosis agents

Global initiatives have been launched to develop improved tuberculosis chemotherapy. New drugs and potential treatment-shortening regimens require careful assessment in clinical trials, but existing markers of treatment outcome-clinical cure and relapse-require prolonged follow-up of patients. There is, therefore, a need to find alternative biomarkers or surrogate endpoints predictive of response. Effective treatment requires drugs with sterilising activity to produce clinical cure without relapse, and thus a useful biomarker for a drug under trial must predict the likelihood of relapse. We explore the strengths and weaknesses of existing biomarkers, which assess either host response or mycobacterial load. Change in mycobacterial burden is likely to be the best indicator of treatment outcome, but the optimum study techniques remain undefined. Finally, we propose methods to assess candidate markers, and how these candidate markers could be implemented in future clinical trials.

Effect of cigarette smoking on sputum smear conversion in adults with active pulmonary tuberculosis

Although factors influencing sputum smear conversion in tuberculosis have been studied well, the effect of smoking is largely unknown. Excluding those with incomplete history or drug resistant isolates, 339 patients out of the 526 sputum positive patients registered between 1998 and 2000 were studied. At the end of 2 months, smokers and non-smokers converted with almost the same frequency to a negative sputum status {P=0.065, OR (95%CI) 0.47 (0.21-1.06)}. Although gender or age had no effect on sputum conversion with respect to smoking status, expatriate smokers as a whole showed a significant difference. (P=0.039). On applying logistic regression model, smokers with far advanced radiographic abnormalities (P<0.038) or with 3+ smear status (P=0.011), were found to have a less chance of an early smear conversion. In conclusion smoking did not influence sputum smear conversion in tuberculosis. However, as expatriate smokers and smokers with advanced disease showed a delay in smear conversion, smoking should be discouraged in patients with pulmonary tuberculosis.

Detection and drug-susceptibility testing of M. tuberculosis from sputum samples using luciferase reporter phage: comparison with the Mycobacteria Growth Indicator Tube (MGIT) system

Rapid diagnosis of drug-resistant M.tuberculosis (Mtb) is desirable worldwide. We (i) describe a new luciferase reporter phage (LRP), phAE142 for this purpose; (ii) compare it to the automated MGIT 960 for time-to-detection of Mtb in clinical specimens; and (iii) evaluate its use for species confirmation and antibiotic susceptibility testing(AST) of Mtb. Twenty sputum samples were inoculated for testing by LRP, or by MGIT 960. After "positives" were identified by either method, the LRP was used for confirmation of Mtb complex (TBC) and for AST. The LRP method proved comparably efficient to MGIT 960 at detecting Mtb. Using an antibiotic uniquely inhibiting TBC with LRP provided species assignment, concurrently with AST, in a median of 3 days, with a sensitivity of 97%. Overall agreement in susceptibility results was 96%. Reliable susceptibility results and identification of TBC can be completed in a median of 12 days (range 8 to 16d) with LRP applied to sputum samples.

Oxidative stress response genes in Mycobacterium tuberculosis: role of ahpC in resistance to peroxynitrite and stage-specific survival in macrophages

The Mycobacterium tuberculosis ahpC gene, encoding the mycobacterial orthologue of alkylhydroperoxide reductase, undergoes an unusual regulatory cycle. The levels of AhpC alternate between stages of expression silencing in virulent strains grown as aerated cultures, secondary to a natural loss of the regulatory oxyR function in all strains of the tubercle bacillus, and expression activation in static bacilli by a yet undefined mechanism. The reasons for this unorthodox regulatory cycle controlling expression of an antioxidant factor are currently not known. In this work, M. tuberculosis H37Rv and Mycobacterium smegmatis mc(2)155 ahpC knockout mutants were tested for sensitivity to reactive nitrogen intermediates, in particular peroxynitrite, a highly reactive combinatorial product of reactive nitrogen and oxygen species, and sensitivity to bactericidal mechanisms in resting and activated macrophages. Both M. tuberculosis ahpC::Km(r) and M. smegmatis ahpC::Km(r) showed increased susceptibility to peroxynitrite. In contrast, inactivation of ahpC in M. tuberculosis did not cause increased sensitivity to donors of NO alone. M. tuberculosis ahpC::Km(r) also showed decreased survival in unstimulated macrophages, but the effect was no longer detectable upon IFNgamma activation. These studies establish a specific role for ahpC in antioxidant defences involving peroxynitrite and most likely additional cidal mechanisms in macrophages, with the regulatory cycle likely contributing to survival upon coming out of the stationary phase during dormancy (latent infection) or upon transmission to a new host.

Serial counts of Mycobacterium tuberculosis in sputum as surrogate markers of the sterilising activity of rifampicin and pyrazinamide in treating pulmonary tuberculosis

BACKGROUND

Since the sterilising activity of new antituberculosis drugs is difficult to assess by conventional phase III studies, surrogate methods related to eventual relapse rates are required.

METHODS

A suitable method is suggested by a retrospective analysis of viable counts of Mycobacterium tuberculosis in 12-hr sputum collections from 122 newly diagnosed patients with pulmonary tuberculosis in Nairobi, done pretreatment and at 2, 7, 14 and 28 days. Treatment was with isoniazid and streptomycin, supplemented with either thiacetazone (SHT) or rifampicin + pyrazinamide (SHRZ).

RESULTS

During days 0-2, a large kill due to isoniazid occurred, unrelated to treatment or HIV status; thereafter it decreased exponentially. SHRZ appeared to have greater sterilising activity than SHT during days 2-7 (p = 0.044), due to rifampicin, and during days 14-28, probably due mainly to pyrazinamide. The greatest discrimination between SHRZ and SHT treatments was found between regression estimates of kill over days 2-28 (p = 0.0005) in patients who remained positive up to 28 days with homogeneous kill rates. No associations were found between regression estimates and the age, sex, and extent of disease or cavitation. An increased kill in HIV seropositive patients, unrelated to the treatment effect, was evident during days 2-28 (p = 0.007), mainly during days 2-7.

CONCLUSIONS

Surrogate marker studies should either be in small groups treated with monotherapy during days 2 to about 7 or as add-ons or replacements in isoniazid-containing standard regimens from days 2 to 28 in large groups.

Mapping of Mycobacterium tuberculosis katG promoters and their differential expression in infected macrophages

Intracellular pathogenic bacteria, including Mycobacterium tuberculosis, frequently have multitiered defense mechanisms ensuring their survival in host phagocytic cells. One such defense determinant in M. tuberculosis is the katG gene, which encodes an enzyme with catalase, peroxidase, and peroxynitritase activities. KatG is considered to be important for protection against reactive oxygen and nitrogen intermediates produced by phagocytic cells. However, KatG also activates the front-line antituberculosis drug isoniazid, hence rendering M. tuberculosis exquisitely sensitive to this compound. In this context, katG expression represents a double-edged sword, as it is an important virulence determinant but at the same time its activity levels determine sensitivity to INH. Thus, it is important to delineate the regulation and expression of katG, as this not only can aid understanding of how M. tuberculosis survives and persists in the host but also may provide information of relevance for better management of INH therapy. Here, we report the first extensive analysis of the katG promoter activity examined both in vitro and in vivo. Using S1 nuclease protection analysis, we mapped the katG mRNA 5' ends and demonstrated that two promoters, P(1)furA and P(1)katG, control transcription of katG. The furA and katG genes are cotranscribed from P(1)furA. Both P(1)furA and P(1)katG promoters show induction upon challenge with hydrogen peroxide and cumene hydroperoxide. Studies carried out using the transcriptional fusions P(1)furA-gfp, P(1)katG-gfp, and P(1)furA-P(1)katG-gfp confirmed the existence of two katG promoters. In addition, we showed that both promoters are expressed in vivo during intracellular growth of virulent M. tuberculosis H37Rv. P(1)furA is induced early upon infection, and P(1)katG becomes active only upon extended growth in macrophages. These studies delineate the transcriptional organization of the furA-katG region and indicate differential regulation in vivo of the two katG promoters. These phenomena most likely reflect the differing demands at sequential stages of the infection cycle and may provide information for improved understanding of host-pathogen interactions in tuberculosis and for further optimization of INH chemotherapy.

Adult tuberculosis in the 21st century: pathogenesis, clinical features, and management

This article reviews the significant advances in the past year in the basic and clinical aspects of adult tuberculosis (TB). Further research has deepened our understanding of host susceptibility and resistance mechanisms, including cytotoxicity, apoptosis, and antimicrobial polypeptides such as granulysin. Studies have confirmed the effects of HIV infection on risk of disease and disease manifestations, and have defined the effects of HIV on TB transmission. Recent studies also indicate a possible role for extended treatment of active disease and latent infection in HIV-1 infected individuals. Multidrug-resistant disease has been reported on every continent; rapid molecular approaches to the simultaneous diagnosis of TB and detection of rifampin resistance may facilitate prompt initiation of treatment. TB remains one of the major problems in global health.

Inhibition of isoniazid-induced expression of Mycobacterium tuberculosis antigen 85 in sputum: potential surrogate marker in tuberculosis chemotherapy trials

Mycobacterium tuberculosis antigen 85 is induced in vitro by isoniazid (INH); its sustained induction in sputum during tuberculosis (TB) therapy predicts relapse. In this trial, rifampin or rifalazil inhibited the induction of sputum antigen 85 by INH in a dose-dependent fashion. This approach may facilitate the evaluation of new TB drugs.