Direct Susceptibility Testing of Mycobacterium tuberculosis for Pyrazinamide by Use of the Bactec MGIT 960 System.

Pyrazinamide (PZA) is a key antituberculosis drug, yet no rapid susceptibility test is commercially available. PZA drug susceptibility testing (DST) was performed directly on sputum samples from 327 patients and compared with the indirect method by using the Bactec MGIT 960 system in the context of patient screening for participation in a drug trial. Compared to standard indirect PZA DST, direct DST was successful in only 59% of cases, but results obtained were highly accurate and available faster. Agreement between the direct and indirect methods varied from 90 to 100% in each laboratory. The median times for obtaining PZA results from the time when the specimen was collected ranged from 11 to 16 days for the direct test and 18 to 95 days for the indirect test across laboratories. The direct method is accurate and reproducible across laboratories. It can be expected to accelerate results in >50% of cases, but it cannot replace indirect DST for PZA. Phenotypic methods remain the gold standard for DST in drug trials. If future studies can optimize the method to decrease the number of uninterpretable results, direct MGIT DST could be the new phenotypic DST standard for clinical trials, providing more rapid detection of resistance to new drugs in experimental regimens.

What is the most reliable solid culture medium for tuberculosis treatment trials?

We conducted a prospective study to determine which solid medium is the most reliable overall and after two months of therapy to detect Mycobacterium tuberculosis complex (MTB). MTB isolation and contamination rates on LJ and Middlebrook 7H10 and 7H11 agar with and without selective antibiotics were examined in a single laboratory and compared against a constructed reference standard and MGIT 960 results. Of 50 smear positive adults with pulmonary TB enrolled, 45 successfully completed standard treatment. Two spot sputum specimens were collected before treatment and at week 8 and one spot specimen each at weeks 2, 4, 6, and 12. The MTB recovery rate among all solid media for pre-treatment specimens was similar. After 8 weeks, selective (S) 7H11 had the highest positivity rate. Latent class analysis was used to construct the primary reference standard. The 98.7% sensitivity of 7H11S (95% Wilson confidence interval 96.4%-99.6%) was highest among the 5 solid media (P = 0.003 by bootstrap); the 82.6% specificity of 7H10S (95% CI 75.7%-87.8%) was highest (P = 0.098). Our results support 7H11S as the medium of choice. Further studies in different areas where recovery and contamination are likely to vary, are recommended.

Treatment outcomes of new tuberculosis patients hospitalized in Kampala, Uganda: a prospective cohort study.

BACKGROUND: In most resource limited settings, new tuberculosis (TB) patients are usually treated as outpatients. We sought to investigate the reasons for hospitalisation and the predictors of poor treatment outcomes and mortality in a cohort of hospitalized new TB patients in Kampala, Uganda. METHODS AND FINDINGS: Ninety-six new TB patients hospitalised between 2003 and 2006 were enrolled and followed for two years. Thirty two were HIV-uninfected and 64 were HIV-infected. Among the HIV-uninfected, the commonest reasons for hospitalization were low Karnofsky score (47%) and need for diagnostic evaluation (25%). HIV-infected patients were commonly hospitalized due to low Karnofsky score (72%), concurrent illness (16%) and diagnostic evaluation (14%). Eleven HIV uninfected patients died (mortality rate 19.7 per 100 person-years) while 41 deaths occurred among the HIV-infected patients (mortality rate 46.9 per 100 person years). In all patients an unsuccessful treatment outcome (treatment failure, death during the treatment period or an unknown outcome) was associated with duration of TB symptoms, with the odds of an unsuccessful outcome decreasing with increasing duration. Among HIV-infected patients, an unsuccessful treatment outcome was also associated with male sex (P = 0.004) and age (P = 0.034). Low Karnofsky score (aHR = 8.93, 95% CI 1.88 - 42.40, P = 0.001) was the only factor significantly associated with mortality among the HIV-uninfected. Mortality among the HIV-infected was associated with the composite variable of CD4 and ART use, with patients with baseline CD4 below 200 cells/µL who were not on ART at a greater risk of death than those who were on ART, and low Karnofsky score (aHR = 2.02, 95% CI 1.02 - 4.01, P = 0.045). CONCLUSION: Poor health status is a common cause of hospitalisation for new TB patients. Mortality in this study was very high and associated with advanced HIV Disease and no use of ART.

How we determined the most reliable solid medium for studying treatment of tuberculosis.

Phase 2 clinical trials for tuberculosis (TB) treatment require reliable culture methods to determine presence or absence of Mycobacterium tuberculosis (Mtb) over the course of therapy, as these trials are based primarily on bacteriological endpoints. We evaluate which of 5 solid media is most reliable: Lowenstein-Jensen (LJ) egg-base medium and 4 Middlebrook agar media (nonselective 7H10 and 7H11 and selective 7H10 and 7H11). We analyze 393 specimens from 50 HIV-negative Ugandan adults with newly-diagnosed, pulmonary TB and high acid-fast bacillus smear grade. Specimens were collected every 2-4 weeks during the first 12 weeks of therapy. We compare the results for each culture to 2 composite reference standards--one that was deemed positive if any solid culture was positive for Mtb and another based on latent-class analysis. Both reference standards established that the 2 selective Middlebrook media most reliably determine the presence or absence of Mtb (P < 0.003), largely because of their lower contamination rates. We also showed that results on Middlebrook media were similar to each other, while LJ was most frequently discordant. Contaminated results appeared more likely to be truly negative than to harbor undetected Mtb.

A metabolic biosignature of early response to anti-tuberculosis treatment.

BACKGROUND: The successful treatment of tuberculosis (TB) requires long-term multidrug chemotherapy. Clinical trials to evaluate new drugs and regimens for TB treatment are protracted due to the slow clearance of Mycobacterium tuberculosis (Mtb) infection and the lack of early biomarkers to predict treatment outcome. Advancements in the field of metabolomics make it possible to identify metabolic profiles that correlate with disease states or successful chemotherapy. However, proof-of-concept of this approach has not been provided for a TB-early treatment response biosignature (TB-ETRB). METHODS: Urine samples collected at baseline and during treatment from 48 Ugandan and 39 South African HIV-seronegative adults with pulmonary TB were divided into discovery and qualification sets, normalized to creatinine concentration, and analyzed by liquid chromatography-mass spectrometry to identify small molecule molecular features (MFs) in individual patient samples. A biosignature that distinguished baseline and 1 month treatment samples was selected by pairwise t-test using data from two discovery sample sets. Hierarchical clustering and repeated measures analysis were applied to additional sample data to down select molecular features that behaved consistently between the two clinical sites and these were evaluated by logistic regression analysis. RESULTS: Analysis of discovery samples identified 45 MFs that significantly changed in abundance at one month of treatment. Down selection using an extended set of discovery samples and qualification samples confirmed 23 MFs that consistently changed in abundance between baseline and 1, 2 and 6 months of therapy, with 12 MFs achieving statistical significance (p < 0.05). Six MFs classified the baseline and 1 month samples with an error rate of 11.8%. CONCLUSIONS: These results define a urine based TB-early treatment response biosignature (TB-ETRB) applicable to different parts of Africa, and provide proof-of-concept for further evaluation of this technology in monitoring clinical responses to TB therapy.

Elucidating emergence and transmission of multidrug-resistant tuberculosis in treatment experienced patients by whole genome sequencing.

BACKGROUND: Understanding the emergence and spread of multidrug-resistant tuberculosis (MDR-TB) is crucial for its control. MDR-TB in previously treated patients is generally attributed to the selection of drug resistant mutants during inadequate therapy rather than transmission of a resistant strain. Traditional genotyping methods are not sufficient to distinguish strains in populations with a high burden of tuberculosis and it has previously been difficult to assess the degree of transmission in these settings. We have used whole genome analysis to investigate M. tuberculosis strains isolated from treatment experienced patients with MDR-TB in Uganda over a period of four years. METHODS AND FINDINGS: We used high throughput genome sequencing technology to investigate small polymorphisms and large deletions in 51 Mycobacterium tuberculosis samples from 41 treatment-experienced TB patients attending a TB referral and treatment clinic in Kampala. This was a convenience sample representing 69% of MDR-TB cases identified over the four year period. Low polymorphism was observed in longitudinal samples from individual patients (2-15 SNPs). Clusters of samples with less than 50 SNPs variation were examined. Three clusters comprising a total of 8 patients were found with almost identical genetic profiles, including mutations predictive for resistance to rifampicin and isoniazid, suggesting transmission of MDR-TB. Two patients with previous drug susceptible disease were found to have acquired MDR strains, one of which shared its genotype with an isolate from another patient in the cohort. CONCLUSIONS: Whole genome sequence analysis identified MDR-TB strains that were shared by more than one patient. The transmission of multidrug-resistant disease in this cohort of retreatment patients emphasises the importance of early detection and need for infection control. Consideration should be given to rapid testing for drug resistance in patients undergoing treatment to monitor the emergence of resistance and permit early intervention to avoid onward transmission.

Variability of infectious aerosols produced during coughing by patients with pulmonary tuberculosis.

RATIONALE: Mycobacterium tuberculosis is transmitted by infectious aerosols, but assessing infectiousness currently relies on sputum microscopy that does not accurately predict the variability in transmission. OBJECTIVES: To evaluate the feasibility of collecting cough aerosols and the risk factors for infectious aerosol production from patients with pulmonary tuberculosis (TB) in a resource-limited setting. METHODS: We enrolled subjects with suspected TB in Kampala, Uganda and collected clinical, radiographic, and microbiological data in addition to cough aerosol cultures. A subset of 38 subjects was studied on 2 or 3 consecutive days to assess reproducibility. MEASUREMENTS AND MAIN RESULTS: M. tuberculosis was cultured from cough aerosols of 28 of 101 (27.7%; 95% confidence interval [CI], 19.9-37.1%) subjects with culture-confirmed TB, with a median 16 aerosol cfu (range, 1-701) in 10 minutes of coughing. Nearly all (96.4%) cultivable particles were 0.65 to 4.7 µm in size. Positive aerosol cultures were associated with higher Karnofsky performance scores (P = 0.016), higher sputum acid-fast bacilli smear microscopy grades (P = 0.007), lower days to positive in liquid culture (P = 0.004), stronger cough (P = 0.016), and fewer days on TB treatment (P = 0.047). In multivariable analyses, cough aerosol cultures were associated with a salivary/mucosalivary (compared with purulent/mucopurulent) appearance of sputum (odds ratio, 4.42; 95% CI, 1.23-21.43) and low days to positive (per 1-d decrease; odds ratio, 1.17; 95% CI, 1.07-1.33). The within-test (kappa, 0.81; 95% CI, 0.68-0.94) and interday test (kappa, 0.62; 95% CI, 0.43-0.82) reproducibility were high. CONCLUSIONS: A minority of patients with TB (28%) produced culturable cough aerosols. Collection of cough aerosol cultures is feasible and reproducible in a resource-limited setting.

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.

A novel metabolite of antituberculosis therapy demonstrates host activation of isoniazid and formation of the isoniazid-NAD+ adduct.

One of the most effective and widely used antituberculosis (anti-TB) drugs is isoniazid (INH), a prodrug activated via oxidation that forms an adduct with NAD(+) to inhibit NADH-dependent targets of Mycobacterium tuberculosis, such as enoyl-acyl carrier protein reductase (InhA). The metabolic by-products and potentially toxic intermediates resulting from INH therapy have been identified through a large body of work. However, an INH-NAD adduct or structures related to this adduct have not been identified in specimens from human TB patients or animal models of TB. Analyses by mass spectrometry of urine collected from TB patients in a study conducted by the NIAID-funded Tuberculosis Research Unit identified 4-isonicotinoylnicotinamide (C(12)H(9)N(3)O(2)) as a novel metabolite of INH therapy. This compound was formed by M. tuberculosis strains in a KatG-dependent manner but could also be produced by mice treated with INH independent of an M. tuberculosis infection. Thus, the 4-isonicotinoylnicotinamide observed in human urine samples is likely derived from the degradation of oxidized INH-NAD adducts and provides direct evidence of host INH activation.

CDC/NIH Workshop. Tuberculosis biomarker and surrogate endpoint research roadmap.

The Centers for Disease Control and Prevention and National Institutes of Health convened a multidisciplinary meeting to discuss surrogate markers of treatment response in tuberculosis. The goals were to assess recent surrogate marker research and to provide specific recommendations for (1) the qualification and validation of biomarkers of treatment outcome; (2) the standardization of specimen and data collection for future clinical trials, including a minimum set of samples and collection time points; and (3) the creation ofa specimen repository to support biomarker testing. This article summarizes these recommendations and provides a roadmap for their implementation.

Effectiveness of the standard WHO recommended retreatment regimen (category II) for tuberculosis in Kampala, Uganda: a prospective cohort study.

BACKGROUND: Each year, 10%-20% of patients with tuberculosis (TB) in low- and middle-income countries present with previously treated TB and are empirically started on a World Health Organization (WHO)-recommended standardized retreatment regimen. The effectiveness of this retreatment regimen has not been systematically evaluated. METHODS AND FINDINGS: From July 2003 to January 2007, we enrolled smear-positive, pulmonary TB patients into a prospective cohort to study treatment outcomes and mortality during and after treatment with the standardized retreatment regimen. Median time of follow-up was 21 months (interquartile range 12-33 months). A total of 29/148 (20%) HIV-uninfected and 37/140 (26%) HIV-infected patients had an unsuccessful treatment outcome. In a multiple logistic regression analysis to adjust for confounding, factors associated with an unsuccessful treatment outcome were poor adherence (adjusted odds ratio [aOR] associated with missing half or more of scheduled doses 2.39; 95% confidence interval (CI) 1.10-5.22), HIV infection (2.16; 1.01-4.61), age (aOR for 10-year increase 1.59; 1.13-2.25), and duration of TB symptoms (aOR for 1-month increase 1.12; 1.04-1.20). All patients with multidrug-resistant TB had an unsuccessful treatment outcome. HIV-infected individuals were more likely to die than HIV-uninfected individuals (p<0.0001). Multidrug-resistant TB at enrollment was the only common risk factor for death during follow-up for both HIV-infected (adjusted hazard ratio [aHR] 17.9; 6.0-53.4) and HIV-uninfected (14.7; 4.1-52.2) individuals. Other risk factors for death during follow-up among HIV-infected patients were CD4<50 cells/ml and no antiretroviral treatment (aHR 7.4, compared to patients with CD4≥200; 3.0-18.8) and Karnofsky score <70 (2.1; 1.1-4.1); and among HIV-uninfected patients were poor adherence (missing half or more of doses) (3.5; 1.1-10.6) and duration of TB symptoms (aHR for a 1-month increase 1.9; 1.0-3.5). CONCLUSIONS: The recommended regimen for retreatment TB in Uganda yields an unacceptable proportion of unsuccessful outcomes. There is a need to evaluate new treatment strategies in these patients.

Rhomboid homologs in mycobacteria: insights from phylogeny and genomic analysis.

BACKGROUND: Rhomboids are ubiquitous proteins with diverse functions in all life kingdoms, and are emerging as important factors in the biology of some pathogenic apicomplexa and Providencia stuartii. Although prokaryotic genomes contain one rhomboid, actinobacteria can have two or more copies whose sequences have not been analyzed for the presence putative rhomboid catalytic signatures. We report detailed phylogenetic and genomic analyses devoted to prokaryotic rhomboids of an important genus, Mycobacterium. RESULTS: Many mycobacterial genomes contained two phylogenetically distinct active rhomboids orthologous to Rv0110 (rhomboid protease 1) and Rv1337 (rhomboid protease 2) of Mycobacterium tuberculosis H37Rv, which were acquired independently. There was a genome-wide conservation and organization of the orthologs of Rv1337 arranged in proximity with glutamate racemase (mur1), while the orthologs of Rv0110 appeared evolutionary unstable and were lost in Mycobacterium leprae and the Mycobacterium avium complex. The orthologs of Rv0110 clustered with eukaryotic rhomboids and contained eukaryotic motifs, suggesting a possible common lineage. A novel nonsense mutation at the Trp73 codon split the rhomboid of Mycobacterium avium subsp. Paratuberculosis into two hypothetical proteins (MAP2425c and MAP2426c) that are identical to MAV_1554 of Mycobacterium avium. Mycobacterial rhomboids contain putative rhomboid catalytic signatures, with the protease active site stabilized by Phenylalanine. The topology and transmembrane helices of the Rv0110 orthologs were similar to those of eukaryotic secretase rhomboids, while those of Rv1337 orthologs were unique. Transcription assays indicated that both mycobacterial rhomboids are possibly expressed. CONCLUSIONS: Mycobacterial rhomboids are active rhomboid proteases with different evolutionary history. The Rv0110 (rhomboid protease 1) orthologs represent prokaryotic rhomboids whose progenitor may be the ancestors of eukaryotic rhomboids. The Rv1337 (rhomboid protease 2) orthologs appear more stable and are conserved nearly in all mycobacteria, possibly alluding to their importance in mycobacteria. MAP2425c and MAP2426c provide the first evidence for a split homologous rhomboid, contrasting whole orthologs of genetically related species. Although valuable insights to the roles of rhomboids are provided, the data herein only lays a foundation for future investigations for the roles of rhomboids in mycobacteria.

The impact of mouse passaging of Mycobacterium tuberculosis strains prior to virulence testing in the mouse and guinea pig aerosol models.

BACKGROUND: It has been hypothesized that the virulence of lab-passaged Mycobacterium tuberculosis and recombinant M. tuberculosis mutants might be reduced due to multiple in vitro passages, and that virulence might be augmented by passage of these strains through mice before quantitative virulence testing in the mouse or guinea pig aerosol models. METHODOLOGY/PRINCIPAL FINDINGS: By testing three M. tuberculosis H37Rv samples, one deletion mutant, and one recent clinical isolate for survival by the quantitative organ CFU counting method in mouse or guinea pig aerosol or intravenous infection models, we could discern no increase in bacterial fitness as a result of passaging of M. tuberculosis strains in mice prior to quantitative virulence testing in two animal models. Surface lipid expression as assessed by neutral red staining and thin-layer chromatography for PDIM analysis also failed to identify virulence correlates. CONCLUSIONS/SIGNIFICANCE: These results indicate that animal passaging of M. tuberculosis strains prior to quantitative virulence testing in mouse or guinea pig models does not enhance or restore potency to strains that may have lost virulence due to in vitro passaging. It is critical to verify virulence of parental strains before genetic manipulations are undertaken and comparisons are made.

Comparison of rapid tests for detection of rifampicin-resistant Mycobacterium tuberculosis in Kampala, Uganda.

BACKGROUND: Drug resistant tuberculosis (TB) is a growing concern worldwide. Rapid detection of resistance expedites appropriate intervention to control the disease. Several technologies have recently been reported to detect rifampicin resistant Mycobacterium tuberculosis directly in sputum samples. These include phenotypic culture based methods, tests for gene mutations and tests based on bacteriophage replication. The aim of the present study was to assess the feasibility of implementing technology for rapid detection of rifampicin resistance in a high disease burden setting in Africa. METHODS: Sputum specimens from re-treatment TB patients presenting to the Mulago Hospital National TB Treatment Centre in Kampala, Uganda, were examined by conventional methods and simultaneously used in one of the four direct susceptibility tests, namely direct BACTEC 460, Etest, "in-house" phage test, and INNO- Rif.TB. The reference method was the BACTEC 460 indirect culture drug susceptibility testing. Test performance, cost and turn around times were assessed. RESULTS: In comparison with indirect BACTEC 460, the respective sensitivities and specificities for detecting rifampicin resistance were 100% and 100% for direct BACTEC and the Etest, 94% and 95% for the phage test, and 87% and 87% for the Inno-LiPA assay. Turn around times ranged from an average of 3 days for the INNO-LiPA and phage tests, 8 days for the direct BACTEC 460 and 20 days for the Etest. All methods were faster than the indirect BACTEC 460 which had a mean turn around time of 24 days. The cost per test, including labour ranged from $18.60 to $41.92 (USD). CONCLUSION: All four rapid technologies were shown capable of detecting rifampicin resistance directly from sputum. The LiPA proved rapid, but was the most expensive. It was noted, however, that the LiPA test allows sterilization of samples prior to testing thereby reducing the risk of accidental laboratory transmission. In contrast the Etest was low cost, but slow and would be of limited assistance when treating patients. The phage test was the least reproducible test studied with failure rate of 27%. The test preferred by the laboratory personnel, direct BACTEC 460, requires further study to determine its accuracy in real-time treatment decisions in Uganda.

Shortening treatment in adults with noncavitary tuberculosis and 2-month culture conversion.

RATIONALE: Cavitary disease and delayed culture conversion have been associated with relapse. Combining patient characteristics and measures of bacteriologic response might allow treatment shortening with current drugs in some patients. OBJECTIVES: To assess whether treatment could be shortened from 6 to 4 months in patients with noncavitary tuberculosis whose sputum cultures converted to negative after 2 months. METHODS: This study was a randomized, open-label equivalence trial. HIV-uninfected adults with noncavitary tuberculosis were treated daily with isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months, followed by 2 months of isoniazid and rifampin. After 4 months, patients with drug-susceptible TB whose sputum cultures on solid media were negative after 8 weeks of treatment were randomly assigned to continue treatment for 2 more months or to stop treatment. Patients were followed for relapse for 30 months after beginning treatment. MEASUREMENTS AND MAIN RESULTS: Enrollment was stopped by the safety monitoring committee after 394 patients were enrolled due to apparent increased risk for relapse in the 4-month arm. A total of 370 patients were eligible for per protocol analysis. Thirteen patients in the 4-month arm relapsed, compared with three subjects in the 6-month arm (7.0 vs. 1.6%; risk difference, 0.054; 95% confidence interval with Hauck-Anderson correction, 0.01-0.10). CONCLUSION: Shortening treatment from 6 to 4 months in adults with noncavitary disease and culture conversion after 2 months using current drugs resulted in a greater relapse rate. The combination of noncavitary disease and 2-month culture conversion was insufficient to identify patients with decreased risk for relapse.

Clinical strains of Mycobacterium tuberculosis display a wide range of virulence in guinea pigs.

Virtually all new tuberculosis vaccine candidates are tested in animals using the laboratory strains H37Rv or Erdman. However, naturally occurring M. tuberculosis infections are caused by strains that are widely different in phenotype and genotype. Very little is known about the characteristics of these clinical isolates in terms of basic biology, virulence and in vivo pathogenicity. In this study, we have used a standardized aerosol infection of guinea pigs to compare in vivo differences between clinical strains of M. tuberculosis. Strains consisted of both drug sensitive and multi-drug resistant (MDR) strains of Beijing and non-Beijing varieties. Collectively, these clinical isolates tested in the guinea pig model exhibited a wide range of virulence. Infection with certain isolates caused severe and rapidly progressive pulmonary and extra-pulmonary lesion necrosis, some of which progressed to atypical cavitary lesions in draining mediastinal and tracheobronchial lymph nodes. The two MDR-TB strains used in this study exhibited low level virulence as determined by bacterial growth, lesion scores and survival. Since infections with clinical M. tuberculosis isolates produce such varied disease, it is unknown whether new tuberculosis vaccines being developed will provide the same level of protection as seen when tested using laboratory challenge strains. The use of appropriate animal models allows for this important question to be addressed.

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.

Use of in-house PCR for identification of Mycobacterium tuberculosis in BACTEC broth cultures of respiratory specimens.

We evaluated the ability of a PCR assay to identify Mycobacterium tuberculosis complex (MTBC) from positive BACTEC 12B broth cultures. A total of 107 sputum samples were processed and inoculated into Ogawa slants and BACTEC 12B vials. At a growth index (GI) > or=30, 1.0 ml of the 12B broth was removed, stored, and assayed with PCR. Molecular results were compared to those obtained by phenotypic identification methods, including the BACTEC NAP method. The average times required to perform PCR and NAP were compared. Of the 107 broth cultures evaluated, 90 were NAP positive, while 91 were PCR positive for MTBC. Of particular interest were three contaminated BACTEC 12B broth cultures yielding microorganisms other than acid-fast bacilli growth with a MTBC that were successfully identified by PCR, resulting in a mean time of 14 days to identify MTBC before NAP identification. These results suggest that PCR could be used as an alternative to the NAP test for the rapid identification of MTBC in BACTEC 12B cultures, particularly in those that contained both MTBC and nontuberculous mycobacteria.

Use of in-house PCR for identification of Mycobacterium tuberculosis in BACTEC broth cultures of respiratory specimens

We evaluated the ability of a PCR assay to identify Mycobacterium tuberculosis complex (MTBC) from positive BACTEC® 12B broth cultures. A total of 107 sputum samples were processed and inoculated into Ogawa slants and BACTEC® 12B vials. At a growth index (GI) > 30, 1.0 ml of the 12B broth was removed, stored, and assayed with PCR. Molecular results were compared to those obtained by phenotypic identification methods, including the BACTEC® NAP method. The average times required to perform PCR and NAP were compared. Of the 107 broth cultures evaluated, 90 were NAP positive, while 91 were PCR positive for MTBC. Of particular interest were three contaminated BACTEC® 12B broth cultures yielding microorganisms other than acid-fast bacilli growth with a MTBC that were successfully identified by PCR, resulting in a mean time of 14 days to identify MTBC before NAP identification. These results suggest that PCR could be used as an alternative to the NAP test for the rapid identification of MTBC in BACTEC® 12B cultures, particularly in those that contained both MTBC and nontuberculous mycobacteria.