Performance of TaqMan array card to detect TB drug resistance on direct specimens

Ability of the MeltPro MTB/PZA Assay to Detect Susceptibility to Pyrazinamide in Rifampin-Resistant Tuberculosis Patients

Prediction of susceptibility to pyrazinamide (PZA) directly from sputum has been challenging. The MeltPro MTB/PZA assay, based on melting curve analysis, can simultaneously detect Mycobacterium tuberculosis and the resistance to PZA from sputum. We aimed to evaluate the MeltPro MTB/PZA assay to predict PZA resistance among rifampin-resistant tuberculosis (RR-TB) patients. We prospectively enrolled RR-TB patients in the registered trials, and their baseline sputum samples were obtained to perform the assay and culture. DNA sequencing of culture isolates was analyzed and used as the reference standard. Sanger sequencing was performed for samples with discrepant results between next-generation sequencing (NGS) and the investigational assay. The main analysis was conducted in the population of patients with interpretable results by both NGS and the assay. A total of 239 patients with RR-TB were screened, and 220 underwent the MeltPro MTB/PZA assay. The assay provided no information for 25 of 220 patients (11.4%). Among the remaining 195 patients, 13 had negative culture or insufficient raw NGS sequencing data, and 15 had indeterminate assay results. A total of 167 patients were included in the main analysis. Against DNA sequencing, the sensitivity, specificity, and negative predictive value of the assay for detecting resistance to PZA were 91.4% (95% confidence interval [CI], 87.1% to 95.6%), 89.9% (95% CI, 85.3% to 94.5%), and 95.2% (95% CI, 91.9% to 98.4%), respectively. In conclusion, the MeltPro MTB/PZA assay is a fast semiautomatic molecular platform to rapidly predict resistance to PZA from sputum and holds promise as a screening tool with satisfactory sensitivity. IMPORTANCE This study evaluated the accuracy of the MeltPro MTB/PZA assay at detecting the presence of PZA resistance through registered clinical trials. Compared to DNA sequencing, the assay had high sensitivity and negative predictive value, suggesting its potential utility as a screening tool in clinical practice. The assay could serve as an ideal primary screening tool in low PZA-resistant M. tuberculosis prevalence settings and could be used as an additional test to identify PZA resistance rapidly and initially in the RR-TB population.

Pyrazinamide-resistant Tuberculosis Obscured From Common Targeted Molecular Diagnostics

Here, we describe a clinical case of pyrazinamide-resistant (PZA-R) tuberculosis (TB) reported as PZA-susceptible (PZA-S) by common molecular diagnostics. Phenotypic susceptibility testing (pDST) indicated PZA-R TB. Targeted Sanger sequencing reported wild-type PncA, indicating PZA-S TB. Whole Genome Sequencing (WGS) by PacBio and IonTorrent both detected deletion of a large portion of pncA, indicating PZA-R. Importantly, both WGS methods showed deletion of part of the primer region targeted by Sanger sequencing. Repeating Sanger sequencing from a culture in presence of PZA returned no result, revealing that 1) two minority susceptible subpopulations had vanished, 2) the PZA-R majority subpopulation harboring the pncA deletion could not be amplified by Sanger primers, and was thus obscured by amplification process. This case demonstrates how a small susceptible subpopulation can entirely obscure majority resistant populations from targeted molecular diagnostics and falsely imply homogenous susceptibility, leading to incorrect diagnosis. To our knowledge, this is the first report of a minority susceptible subpopulation masking a majority resistant population, causing targeted molecular diagnostics to call false susceptibility. The consequence of such genomic events is not limited to PZA. This phenomenon can impact molecular diagnostics' sensitivity whenever the resistance-conferring mutation is not fully within primer-targeted regions. This can be caused by structural changes of genomic context with phenotypic consequence as we report here, or by uncommon mechanisms of resistance. Such false susceptibility calls promote suboptimal treatment and spread of strains that challenge targeted molecular diagnostics. This motivates development of molecular diagnostics unreliant on primer conservation, and impels frequent WGS surveillance for variants that evade prevailing molecular diagnostics.

Highly Sensitive Detection of Isoniazid Heteroresistance in Mycobacterium Tuberculosis by Droplet Digital PCR

Purpose

The drug resistance of Mycobacterium tuberculosis constitutes a major public health threat. Existing approaches make it challenging to detect low levels of drug-resistant TB, also known as heteroresistance (HR), in a population. The recently found droplet digital PCR (ddPCR) is a sensitive method for determining the precise amount of nucleic acid in a sample. We used ddPCR to test the Mycobacterium tuberculosis heteroresistance because it delivers more exact quantitative data without the need for a reference curve.

Patients and Methods

A TaqMan-MGB probe mutation detection assay was developed in order to determine the mutant and wild-type sequences of the isoniazid resistance katG (315) gene. We produced heteroresistant MTB combinations, which were subsequently identified by ddPCR, qPCR, and MeltPro/INH. In addition, 21 clinical sputum samples with positive smears were used to validate each method’s capacity to determine HR in sputum.

Results

We discovered that ddPCR can detect mutant sequences in as few as 0.01% of a combination. DeepMelt TB/INH, which is less sensitive in comparison, cannot detect HR with high resolution and requires a mutation rate of 50% to identify. qPCR likewise has a high resolution of 0.02%, but unlike ddPCR, it cannot determine the exact number of mutations. Our assay is applicable to sputum as well. ddPCR found a katG 315 substitution in two sputums with extremely low values of HR (0.26% and 0.14%). In 21 samples of clinical sputum, the HR prevalence of INH was 9.5%.

Conclusion

This work demonstrates that a well-designed ddPCR HR detection test can detect low levels of HR with high accuracy and consistency and gives new information for the clinical diagnosis of drug resistance.

Simultaneous detection of multiple pathogens with the TaqMan Array Card

Quantitative polymerase chain reaction (qPCR) is a gold standard method for the detection and quantification of pathogenic organisms. Standard qPCR is inexpensive, sensitive and highly specific to the pathogen of interest. While qPCR assays can be multiplexed to allow the detection of multiple organisms in one reaction, it is prohibitively labour intensive to screen large numbers of samples for several pathogens at the same time. The TaqMan Array Card (TAC) is a cost-effective and accurate technique that expands the number of assays that can be simultaneously performed on a sample, with no increase in set-up time and only small reductions in sensitivity. This approach is highly beneficial in settings where there is a need to monitor a large panel of pathogens. We illustrate the application of TAC to the monitoring of gastrointestinal pathogens, which span viral, bacterial, protist and helminth taxa. This protocol outlines the laboratory set-up of a TaqMan Array Card, and some recommended data processing steps to aid in accurate interpretation of the results. A video protocol is additionally provided to assist in the use of the technique.•The TAC is designed primarily for gene expression assays, but has recently been utilised in several studies for pathogen detection in human clinical samples.•We expand the use of TAC for pathogen detection across human, animal and environmental sample types, and have developed a protocol and guidelines for the processing and interpretation of results that circumvents issues with the automated outputs.•This technique is applicable to pathogen or organism detection in any context, if quality nucleic acid extracts can be obtained from the sample type of interest.

Antibiotic heteroresistance in Mycobacterium tuberculosis isolates: a systematic review and meta-analysis

BACKGROUND

Mycobacterium tuberculosis (MTB) is responsible for tuberculosis; that continues to be a public health threat across the globe. Furthermore, increasing heteroresistance (HR)-the presence of resistant and susceptible isolates among MTB strains- has been reported from around the world. This phenomenon can lead to full resistance development and treatment failure.

METHODS

We systematically searched the relevant studies in PubMed, Scopus, and Embase (Until October 21, 2020). The study outcomes revealed the weighted pooled prevalence of antibiotic HR in MTB isolates with subgroup analysis by year, quality of study, and heteroresistance detection method.

RESULTS

A total of 38 studies which had investigated MTB isolates were included in the meta-analysis. Geographically, the highest number of studies were reported from Asia (n  =  24), followed by Africa (n  =  5). Nineteen studies reported HR to isoniazid, with a weighted pooled prevalence of 5% (95% CI 0-12) among 11,761 MTB isolates. Also, there is no important trend for the subgroup analysis by the study period (2001-2014 vs 2015-2017 vs 2018-2020). HR to rifampin was reported in 17 studies, with a weighted pooled prevalence of 7% (95% CI 2-14) among 3782 MTB isolates. HR to fluoroquinolone and ethambutol were reported in 12 and 4 studies, respectively, with weighted pooled prevalence of 10% and 1% among 2153 and 1509 MTB isolates, correspondingly.

CONCLUSION

Based on our analysis, HR in MTB isolates with different frequency rate is present worldwide. Thus, the selection of appropriate and reliable methods for HR detection is crucial for TB eradication.

Diagnostic Accuracy of Pyrazinamide Susceptibility Testing in Mycobacterium tuberculosis: A Systematic Review with Meta-Analysis

Introduction: Pyrazinamide (PZA) susceptibility testing plays a critical role in determining the appropriate treatment regimens for multidrug-resistant tuberculosis. We conducted a systematic review and meta-analysis to evaluate the diagnostic accuracy of sequencing PZA susceptibility tests against culture-based susceptibility testing methods as the reference standard. Methods: We searched the MEDLINE/PubMed, Embase, and Web of Science databases for the relevant records. The QUADAS-2 tool was used to assess the quality of the studies. Diagnostic accuracy measures (i.e., sensitivity and specificity) were pooled with a random-effects model. All statistical analyses were performed with Meta-DiSc (version 1.4, Cochrane Colloquium, Barcelona, Spain), STATA (version 14, Stata Corporation, College Station, TX), and RevMan (version 5.3, The Nordic Cochrane Centre, the Cochrane Collaboration, Copenhagen, Denmark) software. Results: A total of 72 articles, published between 2000 and 2019, comprising data for 8,701 isolates of Mycobacterium tuberculosis were included in the final analysis. The pooled sensitivity and specificity of the PZA sequencing test against all reference tests (the combination of BACTEC mycobacteria growth indicator tube 960 (MGIT 960), BACTEC 460, and proportion method) were 87% (95% CI: 85-88) and 94.7% (95% CI: 94-95). The positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and the area under the curve estimates were found to be 12.0 (95% CI: 9.0-16.0), 0.17 (95% CI: 0.13-0.21), 106 (95% CI: 71-158), and 96%, respectively. Deek's test result indicated a low likelihood for publication bias (p = 0.01). Conclusions: Our analysis indicated that PZA sequencing may be used in combination with conventional tests due to the advantage of the time to result and in scenarios where culture tests are not feasible. Further work to improve molecular tests would benefit from the availability of standardized reference standards and improvements to the methodology.

The Role of Molecular Testing in Pediatric Meningitis Surveillance in Southern and East African Countries, 2008-2017

Background

As part of the global Invasive Bacterial Vaccine-Preventable Diseases Surveillance Network, 12 African countries referred cerebrospinal fluid (CSF) samples to South Africa’s regional reference laboratory. We evaluated the utility of real-time polymerase chain reaction (PCR) in detecting and serotyping/grouping Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae (HNS).

Methods

From 2008 to 2017, CSF samples collected from children <5 years old with suspected meningitis underwent routine microbiology testing in-country, and 11 680 samples were submitted for HNS PCR at the regional reference laboratory. Unconditional logistic regression, with adjustment for geographic location, was performed to identify factors associated with PCR positivity.

Results

The overall HNS PCR positivity rate for all countries was 10% (1195 of 11 626 samples). In samples with both PCR and culture results, HNS PCR positivity was 11% (744 of 6747 samples), and HNS culture positivity was 3% (207 of 6747). Molecular serotype/serogroup was assigned in 75% of PCR-positive specimens (762 of 1016). Compared with PCR-negative CSF samples, PCR-positive samples were more often turbid (adjusted odds ratio, 6.80; 95% confidence interval, 5.67–8.17) and xanthochromic (1.72; 1.29–2.28), had elevated white blood cell counts (6.13; 4.71–7.99) and high protein concentrations (5.80; 4.34–7.75), and were more often HNS culture positive (32.70; 23.18–46.12).

Conclusion

PCR increased detection of vaccine-preventable bacterial meningitis in countries where confirmation of suspected meningitis cases is impeded by limited culture capacity.

Systematic review of mutations associated with resistance to the new and repurposed Mycobacterium tuberculosis drugs bedaquiline, clofazimine, linezolid, delamanid and pretomanid

BACKGROUND

Improved genetic understanding of Mycobacterium tuberculosis (MTB) resistance to novel and repurposed anti-tubercular agents can aid the development of rapid molecular diagnostics.

METHODS

Adhering to PRISMA guidelines, in March 2018, we performed a systematic review of studies implicating mutations in resistance through sequencing and phenotyping before and/or after spontaneous resistance evolution, as well as allelic exchange experiments. We focused on the novel drugs bedaquiline, delamanid, pretomanid and the repurposed drugs clofazimine and linezolid. A database of 1373 diverse control MTB whole genomes, isolated from patients not exposed to these drugs, was used to further assess genotype-phenotype associations.

RESULTS

Of 2112 papers, 54 met the inclusion criteria. These studies characterized 277 mutations in the genes atpE, mmpR, pepQ, Rv1979c, fgd1, fbiABC and ddn and their association with resistance to one or more of the five drugs. The most frequent mutations for bedaquiline, clofazimine, linezolid, delamanid and pretomanid resistance were atpE A63P, mmpR frameshifts at nucleotides 192-198, rplC C154R, ddn W88* and ddn S11*, respectively. Frameshifts in the mmpR homopolymer region nucleotides 192-198 were identified in 52/1373 (4%) of the control isolates without prior exposure to bedaquiline or clofazimine. Of isolates resistant to one or more of the five drugs, 59/519 (11%) lacked a mutation explaining phenotypic resistance.

CONCLUSIONS

This systematic review supports the use of molecular methods for linezolid resistance detection. Resistance mechanisms involving non-essential genes show a diversity of mutations that will challenge molecular diagnosis of bedaquiline and nitroimidazole resistance. Combined phenotypic and genotypic surveillance is needed for these drugs in the short term.

Meta-narrative review of molecular methods for diagnosis and monitoring of multidrug-resistant tuberculosis treatment in adults

Early and accurate diagnosis and rigorous clinical and microbiological monitoring of multidrug-resistant tuberculosis (MDR-TB) treatment can curb morbidity and mortality. While others are still under evaluation, the World Health Organization has recommended few novel molecular methods for MDR-TB diagnosis only. We present current molecular methods for diagnosis and monitoring of MDR-TB treatment in TB-endemic settings. A systematic meta-narrative review was conducted according to the RAMESES recommendations. Electronic databases were searched for relevant articles published in English language from January 2013 to June 2018. Based on predefined criteria, two independent reviewers extracted the key messages from relevant articles. Disagreement between them was resolved through discussion and the involvement of a third reviewer, if needed. Key messages were synthesized to create the meta-narratives for method's accuracy, drug-susceptibility capability, and laboratory infrastructure required. We included 33 articles out of 1213 records retrieved, of which 16 (48%) and 12 (36%) were conducted in high- and low-TB-endemic settings, respectively. Xpert® MTB/RIF, GenoType MTBDRplus, GenoType MTBDRsl, FlouroType™ MTBDR, TB TaqMan® array card, and DNA sequencers can accurately guide effective treatment regimens. Molecular bacterial load assay quantifies mycobactericidal impact of these regimens. Although they present inherent advantages compared to the current standard of care, they carry important limitations to implementation and/or scale-up. Therefore, considerable effort must now be directed to implementation and health systems research to maximize these forecasted benefits for individual patient's health outcomes.