Identification of rifampin-resistant Mycobacterium tuberculosis strains by hybridization, PCR, and ligase detection reaction on oligonucleotide microchips

Mutations and insights into the molecular mechanisms of resistance of Mycobacterium tuberculosis to first-line

Genetically antimicrobial resistance in Mycobacterium tuberculosis is currently one of the most important aspects of tuberculosis, considering that there are emerging resistant strains for almost every known drug used for its treatment. There are multiple antimicrobials used for tuberculosis treatment, and the most effective ones are the first-line drugs, which include isoniazid, pyrazinamide, rifampicin, and ethambutol. In this context, understanding the mechanisms of action and resistance of these molecules is essential for proposing new therapies and strategies of treatment. Additionally, understanding how and where mutations arise conferring a resistance profile to the bacteria and their effect on bacterial metabolism is an important requisite to be taken in producing safer and less susceptible drugs to the emergence of resistance. In this review, we summarize the most recent literature regarding novel mutations reported between 2017 and 2022 and the advances in the molecular mechanisms of action and resistance against first-line drugs used in tuberculosis treatment, highlighting recent findings in pyrazinamide resistance involving PanD and, additionally, resistance-conferring mutations for novel drugs such as bedaquiline, pretomanid, delamanid and linezolid.

Synthesis of Cy5-Labelled C5-Alkynyl-modified cytidine triphosphates via Sonogashira coupling for DNA labelling

New applications of palladium-catalyzed Sonogashira-type cross-coupling reaction between C5-halogenated 2'-deoxycytidine-5'-monophosphate and novel cyanine dyes with a terminal alkyne group have been developed. The present methodology allows to synthesize of fluorescently labeled C5-nucleoside triphosphates with different acetylene linkers between the fluorophore and pyrimidine base in good to excellent yields under mild reaction conditions. Modified 2'-deoxycytidine-5'-triphosphates were shown to be good substrates for DNA polymerases and were incorporated into the DNA by polymerase chain reaction.

Spoligotyping of the Mycobacterium tuberculosis complex using on-Chip PCR

AIMS

The aim of this study was to develop a rapid PCR-based method for spoligotyping of Mycobacteria in the microarray format and to compare it to conventional spoligotyping by hybridization.

METHODS AND RESULTS

The method employs the on-Chip PCR technique with primers specific for 43 spacers that separate direct repeats (DRs) in the DR region of mycobacterial DNA. The primers were immobilized on gel-based microarrays, and PCR was performed directly on the chips. The PCR fluorescence images were acquired and processed using a portable fluorescence analyzer equipped with dedicated software. Analysis takes 1.5-2 hours and can be carried out on clinical samples without additional handling. The analytical sensitivity of the method was 103 copies of target DNA. The spoligotyping results of 51 samples produced by the proposed method and by conventional reverse hybridization approach were in full concordance.

CONCLUSIONS

High throughput capacity, computerized data analysis, compact equipment, and reliable results make the on-Chip PCR an attractive alternative to intra- and interspecific spoligotyping of Mycobacterium tuberculosis complex bacteria.

SIGNIFICANCE AND IMPACT OF STUDY

Fast microarray-based spoligotyping technique using on-Chip PCR was developed.

Molecular characteristics of Mycobacterium tuberculosis drug-resistant isolates from HIV- and HIV+ tuberculosis patients in Russia

Background

High burden of drug-resistant (DR) tuberculosis (TB) is a significant threat to national TB control programs all over the world and in the Russian Federation. Different Mycobacterium tuberculosis (MTB) genotypes are hypothesized to have specific characteristics affecting TB control programs. For example, Beijing strains are supposed to have higher mutation rates compared to strains of other genotypes and subsequently higher capability to develop drug-resistance.

Results

Clinical MTB isolates from HIV- and HIV+ patients from four regions of Russia were analyzed for genotypes and mutations conferring resistance to Isoniazid, Rifampicin, Ethambutol, aminoglycosides, and fluoroquinolones. Analysis of genotypes and polymorphism of genomic loci according to the HIV status of the patients – sources of MTB isolates were performed. Studied MTB isolates from HIV- TB patients belonged to 15 genotypes and from HIV + TB patients – to 6 genotypes. Beijing clinical isolates dominated in HIV- (64,7%) and HIV+ (74,4%) groups. Other isolates were of LAM (including LAM1 and LAM9), Ural, and 4 minor groups of genotypes (including 5 subclones T). The spectrum of genotypes in the HIV- group was broader than in the HIV+ group. PR of B0/W148 Beijing was significantly lower than of other Beijing genotypes in susceptible and MDR-XDR isolates. Rates of isolates belonging to non-Beijing genotypes were higher than Beijing in susceptible isolates from HIV- patients.

Conclusions

Beijing genotype isolates prevailed in clinical isolates of all drug susceptibility profiles both from HIV- and HIV+ patients, although B0/W148 Beijing genotype did not dominate in this study. Genome loci and mutations polymorphisms were more pronounced in clinical isolates from HIV- patients, than from HIV+.

Development of Multiplex RT-PCR with Immobilized Primers for Identification of Infectious Human Pneumonia Pathogens

A prototype of a system for the detection of infectious human pneumonia pathogens based on multiplex solid-phase reverse transcription PCR (RT-PCR) was developed. Primers were designed to identify the DNA of six bacterial pneumonia pathogen strains, and the RNA of two viral pathogens of pneumonia: influenza A and SARS-CoV-2. The signal accumulation of elongated immobilized primers occurs due to the incorporation of fluorescently labeled nucleotides in the chain. The signal is detected after all the components of the mixture are removed, which significantly reduces the background signal and increases the sensitivity of the analysis. The use of a specialized detector makes it possible to read the signals of elongated primers directly through the transparent cover film of the reaction chamber. This solution is designed to prevent cross-contamination and is suitable for simultaneous testing of a large number of test samples. The proposed platform is able to detect the presence of several pathogens of pneumonia in a sample and has an open architecture that allows expansion of the range of pathogenic bacteria and viruses that can be detected.

Hydrogel Droplet Microarray for Genotyping Antimicrobial Resistance Determinants in Neisseria gonorrhoeae Isolates

A multiplex assay based on a low-density hydrogel microarray was developed to identify genomic substitutions in N. gonorrhoeae that determine resistance to the currently recommended treatment agents ceftriaxone and azithromycin and the previously used drugs penicillin, tetracycline, and ciprofloxacin. The microarray identifies 74 drug resistance determinants in the N. gonorrhoeae penA, ponA, porB, gyrA, parC, rpsJ, mtrR, bla_TEM, tetM, and 23S rRNA genes. The hydrogel elements were formed by automated dispensing of nanoliter-volume droplets followed by UV-induced copolymerization of NH₂-containing oligonucleotides with gel-forming monomers. Polybutylene terephthalate plates without special modifications were used as microarray substrates. Sequences and concentrations of immobilized oligonucleotides, gel composition, and hybridization conditions were carefully selected, and the median discrimination ratio ranged from 2.8 to 29.4, allowing unambiguous identification of single-nucleotide substitutions. The mutation identification results in a control sample of 180 N. gonorrhoeae isolates were completely consistent with the Sanger sequencing results. In total, 648 clinical N. gonorrhoeae isolates obtained in Russia during the last 5 years were analyzed and genotyped using these microarrays. The results allowed us to draw conclusions about the present situation with antimicrobial susceptibility of N. gonorrhoeae in Russia and demonstrated the possibility of using hydrogel microarrays to control the spread of antibiotic resistance.

Profiling and identification of novel rpoB mutations in rifampicin-resistant Mycobacterium tuberculosis clinical isolates from Pakistan

INTRODUCTION

Rifampicin (RIF) is one of the most effective anti-tuberculosis first-line drugs prescribed along with isoniazid. However, the emergence of RIF resistance Mycobacterium tuberculosis (MTB) isolates is a major issue towards tuberculosis (TB) control program in high MDR TB-burdened countries including Pakistan. Molecular data behind phenotypic resistance is essential for better management of RIF resistance which has been linked with mutations in rpoB gene. Since molecular studies on RIF resistance is limited in Pakistan, the current study was aimed to investigate the molecular data of mutations in rpoB gene behind phenotypic RIF resistance isolates in Pakistan.

METHOD

A total of 322 phenotypically RIF-resistant isolates were randomly selected from National TB Reference Laboratory, Pakistan for sequencing while 380 RIF resistance whole-genome sequencing (WGS) of Pakistani isolates (BioProject PRJEB25972), were also analyzed for rpoB mutations.

RESULT

Among the 702 RIF resistance samples, 675 (96.1%) isolates harbored mutations in rpoB in which 663 (94.4%) were detected within the Rifampicin Resistance Determining Region (RRDR) also known as a mutation hot spot region, including three novel. Among these mutations, 657 (97.3%) were substitutions including 603 (89.3%) single nucleotide polymorphism, 49 (7.25%) double and five (0.8%) triple. About 94.4% of Phenotypic RIF resistance strains, exhibited mutations in RRDR, which were also detectable by GeneXpert.

CONCLUSION

Mutations in the RRDR region of rpoB is a major mechanism of RIF resistance in MTB circulating isolates in Pakistan. Molecular detection of drug resistance is a faster and better approach than phenotypic drug susceptibility testing to reduce the time for transmission of RIF resistance strains in population. Such insights will inform the deployment of anti-TB drug regimens and disease control tools and strategies in high burden settings, such as Pakistan.

Mutations of rpoB, katG, inhA and ahp genes in rifampicin and isoniazid-resistant Mycobacterium tuberculosis in Kyrgyz Republic

Background

The aim of this study was to identify mutations of rpoB, katG, inhA and ahp-genes associated Mycobacterium tuberculosis resistance to rifampicin (RIF) and isoniazid (INH) in Kyrgyz Republic. We studied 633 smear samples from the primary pulmonary tuberculosis (TB) patients. We verified Mycobacterium tuberculosis susceptibility to RIF and INH using culture method of absolute concentrations, and commercially available test named “TB-BIOCHIP” (Biochip-IMB, Moscow, Russian Federation).

Results

For RIF-resistance, TB-BIOCHIP’s sensitivity and specificity were 88% and 97%, 84% and 95% for INH-resistance, and 90% and 97% for multi-drug resistance (MDR). In RIF-resistant strains, TB-BIOCHIP showed mutations in codons 531 (64.8%), 526 (17.3%), 516 (8.1%), 511 (5.4%), 533 (3.2%), 522 (0.6%) and 513 (0.6%) of rpoB gene. The most prevalent was Ser531 > Leu mutation (63.7%). 91.2% of mutations entailing resistance to INH were in katG gene, 7% in inhA gene, and 1.8% in ahpC gene. Ser315→Thr (88.6%) was the most prevalent mutation leading to resistance to INH.

Conclusions

In Kyrgyz Republic, the most prevalent mutation in RIF-resistant strains was Ser531 → Leu in rpoB gene, as opposed to Ser315 → Thr in katG gene in INH-resistant Mycobacterium tuberculosis. In Kyrgyz Republic, the major reservoir of MDR Mycobacterium tuberculosis were strains with combined mutations Ser531 → Leu in rpoB gene and Ser315 → Thr in katG gene. TB-BIOCHIP has shown moderate sensitivity with the advantage of obtaining results in only two days.

Immuno-diagnosis of Mycobacterium tuberculosis in sputum, and reduction of timelines for its positive cultures to within 3 h by pathogen-specific thymidylate kinase expression assays

BACKGROUND

Laboratory diagnosis of Tuberculosis (TB) is traditionally based on microscopy and or culture. Microscopy is however, only sensitive to a specified degree of bacillary load not present in HIV co-infected persons. Traditional cultures of Mycobacterium tuberculosis (M. tb), on the other hand, take weeks to read-thereby delaying the critical decision whether or not, to treat. Although nucleic acids amplification tests (NAATS) applied directly on sputum or cultures can increase the sensitivity for TB diagnosis among those with HIV co-infection as well as reduce time-lines for positive culture detection, they do not replace the need for smear microscopy and culture. We have previously proposed the M. tb DNA-synthetic enzyme thymidylate kinase (aka TMKmt) as an organism-specific growth and proliferation biomarker to reduce time-lines for detection of positive TB cultures. In this study, we explored the secretory levels of TMKmt in M. tb cultures and sputum, towards improving the overall laboratory diagnosis of TB.

METHODS AND RESULTS

Modelling of TMKmt secretion in vitro was done by cloning, expressing and SDS-PAGE/MALDI-TOF detection of purified recombinant TMKmt in E. coli. TMKmt expression profiling in M. tb was done by qRT-PCR assay of related messenger ribonucleic acids (mRNA) and TMKmt antigen detection by Enzyme linked Immuno-absorbent Assay (EIA) among cultures of a pathogenic wild-type Ugandan strain (genotype 1) alongside the H37Rv laboratory strain. Owing to the high-load of pathogen in-culture, direct EIA on limiting dilutions of sputum were done to examine for assay sensitivity. A rise in TMKmt antigen levels was observed at 3 h post-innoculation among in vitro cultures of E. coli. The 1st of several cyclic spikes in TMKmt mRNA and antigen levels were detected at 2.5 h among in vitro cultures of the pathogenic wild-type Ugandan isolate alongside the laboratory M. tb strain. TMKmt antigen was detected up to between 1 × 10-4-1 × 10-5 (containing 10 and 1 CFUs/ml) dilutions of a microscopically designated 1+ (est. Acid Fast Bacillary load of 1 × 105) patient sample.

CONCLUSIONS

Detection of TMKmt expressed mRNA and Ag offers us opportune for instant diagnosis of M. tb in sputum, and reduction of timelines for positive pathogen detection in cultures to within 3 h.

Systematic review, meta-analysis and economic modelling of molecular diagnostic tests for antibiotic resistance in tuberculosis

BACKGROUND

Drug-resistant tuberculosis (TB), especially multidrug-resistant (MDR, resistance to rifampicin and isoniazid) disease, is associated with a worse patient outcome. Drug resistance diagnosed using microbiological culture takes days to weeks, as TB bacteria grow slowly. Rapid molecular tests for drug resistance detection (1 day) are commercially available and may promote faster initiation of appropriate treatment.

OBJECTIVES

To (1) conduct a systematic review of evidence regarding diagnostic accuracy of molecular genetic tests for drug resistance, (2) conduct a health-economic evaluation of screening and diagnostic strategies, including comparison of alternative models of service provision and assessment of the value of targeting rapid testing at high-risk subgroups, and (3) construct a transmission-dynamic mathematical model that translates the estimates of diagnostic accuracy into estimates of clinical impact.

REVIEW METHODS AND DATA SOURCES

A standardised search strategy identified relevant studies from EMBASE, PubMed, MEDLINE, Bioscience Information Service (BIOSIS), System for Information on Grey Literature in Europe Social Policy & Practice (SIGLE) and Web of Science, published between 1 January 2000 and 15 August 2013. Additional 'grey' sources were included. Quality was assessed using quality assessment of diagnostic accuracy studies version 2 (QUADAS-2). For each diagnostic strategy and population subgroup, a care pathway was constructed to specify which medical treatments and health services that individuals would receive from presentation to the point where they either did or did not complete TB treatment successfully. A total cost was estimated from a health service perspective for each care pathway, and the health impact was estimated in terms of the mean discounted quality-adjusted life-years (QALYs) lost as a result of disease and treatment. Costs and QALYs were both discounted at 3.5% per year. An integrated transmission-dynamic and economic model was used to evaluate the cost-effectiveness of introducing rapid molecular testing (in addition to culture and drug sensitivity testing). Probabilistic sensitivity analysis was performed to evaluate the impact on cost-effectiveness of diagnostic and treatment time delays, diagnosis and treatment costs, and associated QALYs.

RESULTS

A total of 8922 titles and abstracts were identified, with 557 papers being potentially eligible. Of these, 56 studies contained sufficient test information for analysis. All three commercial tests performed well when detecting drug resistance in clinical samples, although with evidence of heterogeneity between studies. Pooled sensitivity for GenoType® MTBDRplus (Hain Lifescience, Nehren, Germany) (isoniazid and rifampicin resistance), INNO-LiPA Rif.TB® (Fujirebio Europe, Ghent, Belgium) (rifampicin resistance) and Xpert® MTB/RIF (Cepheid Inc., Sunnyvale, CA, USA) (rifampicin resistance) was 83.4%, 94.6%, 95.4% and 96.8%, respectively; equivalent pooled specificity was 99.6%, 98.2%, 99.7% and 98.4%, respectively. Results of the transmission model suggest that all of the rapid assays considered here, if added to the current diagnostic pathway, would be cost-saving and achieve a reduction in expected QALY loss compared with current practice. GenoType MTBDRplus appeared to be the most cost-effective of the rapid tests in the South Asian population, although results were similar for GeneXpert. In all other scenarios GeneXpert appeared to be the most cost-effective strategy.

CONCLUSIONS

Rapid molecular tests for rifampicin and isoniazid resistance were sensitive and specific. They may also be cost-effective when added to culture drug susceptibility testing in the UK. There is global interest in point-of-care testing and further work is needed to review the performance of emerging tests and the wider health-economic impact of decentralised testing in clinics and primary care, as well as non-health-care settings, such as shelters and prisons.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42011001537.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Association of MDR-TB isolates with clinical characteristics of patients from Northern region of India

PURPOSE

We sought to determine the characteristics and relative frequency of transmission of MDR-TB in North India and their association with the clinical and epidemiological characteristics of TB-patients.

MATERIALS AND METHODS

To achieve the objectives PCR-SSCP, MAS-PCR and direct DNA sequencing were used against 101 Mycobacterium tuberculosis isolates.

RESULTS

Multidrug-resistant-TB isolates were found to be significantly higher (P=0.000) in previously treated patients in comparison to newly diagnosed patients. Further, significant differences (P=0.003) were observed between different age groups (Mean±SD, 28.6±11.77) of the TB patients and multidrug resistance. Most frequent mutations were observed at codons 531 and 315 of rpoB and katG genes, respectively, in MDR-TB isolates.

CONCLUSION

Routine surveillance of resistance to anti-TB drugs will improve timely recognition of MDR-TB cases and help prevent further transmission in Northern India.

A systematic review of rapid drug susceptibility tests for multidrug-resistant tuberculosis using rifampin resistance as a surrogate

BACKGROUND

The emergence of multidrug-resistant tuberculosis (MDR-TB) has prompted the development of rapid drug susceptibility assays with a focus on rifampin in recent years. Systematic reviews with evaluation of predictive values for different assays are scarce.

METHOD

MEDLINE was searched on 6 September 2008 for English articles that contain concurrent original data for generating summary measures of sensitivity, specificity and likelihood ratios of rapid rifampin susceptibility assays.

RESULTS/CONCLUSIONS

Significant heterogeneity was found in likelihood ratios across studies of all assays except nitrate reductase assay and colorimetric assays. Although rapid assays are fairly reliable for ruling out MDR-TB, careful consideration of clinical risk factors is required before using these assays to rule in MDR-TB under different epidemiological settings.

Performance of Cepheid ® Xpert MTB/RIF ® and TB-Biochip ® MDR in two regions of Russia with a high prevalence of drug-resistant tuberculosis

The purpose of this study was to assess the performance of Cepheid® Xpert MTB/RIF® ("Xpert") and TB-Biochip® MDR ("TB-Biochip"). Sputum specimens from adults with presumptive tuberculosis (TB) were homogenized and split for: (1) direct Xpert and microscopy, and (2) concentration for Xpert, microscopy, culture [Lowenstein-Jensen (LJ) solid media and Mycobacteria Growth Indicator Tube® (MGIT)], indirect drug susceptibility testing (DST) using the absolute concentration method and MGIT, and TB-Biochip. In total, 109 of 238 (45.8 %) specimens were culture-positive for Mycobacterium tuberculosis complex (MTBC), and, of these, 67 isolates were rifampicin resistant (RIF-R) by phenotypic DST and 64/67 (95.5 %) were isoniazid resistant (INH-R). Compared to culture of the same specimen, a single direct Xpert was more sensitive for detecting MTBC [95.3 %, 95 % confidence interval (CI), 90.0-98.3 %] than direct (59.6 %, 95 % CI, 50.2-68.5 %) or concentrated smear (85.3 %, 95 % CI, 77.7-91.1 %) or LJ culture (80.8 %, 95 % CI, 72.4-87.5 %); the specificity was 86.0 % (95 % CI, 78.9-91.3 %). Compared with MGIT DST, Xpert correctly identified 98.2 % (95 % CI, 91.5-99.9 %) of RIF-R and 95.5 % (95 % CI, 85.8-99.2 %) of RIF-susceptible (RIF-S) specimens. In a subset of 104 specimens, the sensitivity of TB-Biochip for MTBC detection compared to culture was 97.3 % (95 % CI, 91.0-99.5 %); the specificity was 78.1 % (95 % CI, 61.5-89.9 %). TB-Biochip correctly identified 100 % (95 % CI, 94.2-100 %) of RIF-R, 94.7 % (95 % CI, 76.7-99.7 %) of RIF-S, 98.2 % (95 % CI, 91.4-99.9 %) of INH-R, and 78.6 % (95 % CI, 52.1-94.2 %) of INH-S specimens compared to MGIT DST. Xpert and Biochip were similar in accuracy for detecting MTBC and RIF resistance compared to conventional culture methods.

Study of the rifampin monoresistance mechanism in Mycobacterium tuberculosis

Rifampin (RIF) susceptibility is a key factor in determining the treatment effectiveness of the standardized treatment regimens. In Mycobacterium tuberculosis, both target gene mutation and the efflux pump play major roles in the resistance to antituberculosis drugs. By eliminating RIF-resistant strains with rpoB mutation, the choice of RIF-monoresistant strains may allow us to identify the RIF-specific efflux pump genes. This study explored the RIF monoresistance mechanism in M. tuberculosis. Data from DNA sequencing and MIC measurements revealed that specific mutations, including Ser531Leu and His526Asp in RpoB, show high-level drug resistance. Three-dimensional structure modeling provided further evidence that the affinity between RIF and RpoB mutants was in accordance with the drug resistance level of the corresponding isolates. Furthermore, transcription-level analysis among the nonmutated isolates indicated that three efflux pumps (Rv0783, Rv2936, and Rv0933) might be involved in exporting RIF from the cell. Compared to 8 μg/ml for wild-type Escherichia coli, the MICs for the transgenic E. coli strains with either Rv0783 or Rv2936 were 32 and 16 μg/ml, respectively. In conclusion, our study indicated that several RpoB mutant types, including Ser531Leu and His526Asp, show high-level RIF resistance attributed to low affinity between RpoB mutant proteins and RIF. In addition, this work demonstrates that Rv2936 and Rv0783 may be responsible for low-level resistance to RIF by exporting RIF from cells. The predicted structure of RpoB and the newly identified efflux pumps in this study will provide a novel approach to design new drugs and develop novel diagnosis technologies.

Capillary electrophoresis-single strand conformation polymorphism for the detection of multiple mutations leading to tuberculosis drug resistance

Drug resistant tuberculosis (TB) is a major health problem in both developed and developing countries. Mutations in the Mycobacterium (M.) tuberculosis bacterial genome, such as those to the rpoB gene and mabA-inhA promoter region, have been linked to TB drug resistance in against rifampicin and isoniazid, respectively. The rapid, accurate, and inexpensive identification of these and other mutations leading to TB drug resistance is an essential tool for improving human health. Capillary electrophoresis (CE) single strand conformation polymorphism (SSCP) can be a highly sensitive technique for the detection of genetic mutation that has not been previously explored for drug resistance mutations in M. tuberculosis. This work explores the potential of CE-SSCP through the optimization of variables such as polymer separation matrix concentration, capillary wall coating, electric field strength, and temperature on resolution of mutation detection. The successful detection of an rpoB gene mutation and two mabA-inhA promoter region mutations while simultaneously differentiating a TB-causing mycobacteria from a non-TB bacteria was accomplished using the optimum conditions of 4.5% (w/v) PDMA in a PDMA coated capillary at 20°C using a separation voltage of 278 V/cm. This multiplexed analysis that can be completed in a few hours demonstrates the potential of CE-SSCP to be an inexpensive and rapid analysis method.

Laboratory diagnosis of tuberculosis in resource-poor countries: challenges and opportunities

With an estimated 9.4 million new cases globally, tuberculosis (TB) continues to be a major public health concern. Eighty percent of all cases worldwide occur in 22 high-burden, mainly resource-poor settings. This devastating impact of tuberculosis on vulnerable populations is also driven by its deadly synergy with HIV. Therefore, building capacity and enhancing universal access to rapid and accurate laboratory diagnostics are necessary to control TB and HIV-TB coinfections in resource-limited countries. The present review describes several new and established methods as well as the issues and challenges associated with implementing quality tuberculosis laboratory services in such countries. Recently, the WHO has endorsed some of these novel methods, and they have been made available at discounted prices for procurement by the public health sector of high-burden countries. In addition, international and national laboratory partners and donors are currently evaluating other new diagnostics that will allow further and more rapid testing in point-of-care settings. While some techniques are simple, others have complex requirements, and therefore, it is important to carefully determine how to link these new tests and incorporate them within a country's national diagnostic algorithm. Finally, the successful implementation of these methods is dependent on key partnerships in the international laboratory community and ensuring that adequate quality assurance programs are inherent in each country's laboratory network.

Evaluation of one- and two-color gene expression arrays for microbial comparative genome hybridization analyses in routine applications

DNA microarray technology has already revolutionized basic research in infectious diseases, and whole-genome sequencing efforts have allowed for the fabrication of tailor-made spotted microarrays for an increasing number of bacterial pathogens. However, the application of microarrays in diagnostic microbiology is currently hampered by the high costs associated with microarray experiments and the specialized equipment needed. Here, we show that a thorough bioinformatic postprocessing of the microarray design to reduce the amount of unspecific noise also allows the reliable use of spotted gene expression microarrays for gene content analyses. We further demonstrate that the use of only single-color labeling to halve the costs for dye-labeled nucleotides results in only a moderate decrease in overall specificity and sensitivity. Therefore, gene expression microarrays using only single-color labeling can also reliably be used for gene content analyses, thus reducing the costs for potential routine applications such as genome-based pathogen detection or strain typing.

Basic concepts of microarrays and potential applications in clinical microbiology

The introduction of in vitro nucleic acid amplification techniques, led by real-time PCR, into the clinical microbiology laboratory has transformed the laboratory detection of viruses and select bacterial pathogens. However, the progression of the molecular diagnostic revolution currently relies on the ability to efficiently and accurately offer multiplex detection and characterization for a variety of infectious disease pathogens. Microarray analysis has the capability to offer robust multiplex detection but has just started to enter the diagnostic microbiology laboratory. Multiple microarray platforms exist, including printed double-stranded DNA and oligonucleotide arrays, in situ-synthesized arrays, high-density bead arrays, electronic microarrays, and suspension bead arrays. One aim of this paper is to review microarray technology, highlighting technical differences between them and each platform's advantages and disadvantages. Although the use of microarrays to generate gene expression data has become routine, applications pertinent to clinical microbiology continue to rapidly expand. This review highlights uses of microarray technology that impact diagnostic microbiology, including the detection and identification of pathogens, determination of antimicrobial resistance, epidemiological strain typing, and analysis of microbial infections using host genomic expression and polymorphism profiles.

Separate production of single-stranded DNA is not necessary: circuit denaturation of double-stranded DNA followed by hybridization of single strands on oligonucleotide microchips

An approach to circuit renaturation-hybridization of dsDNA on oligonucleotide microchips is described. A close circuit cycling device has been developed, and the feasibility of the proposed technique was demonstrated on two platforms. First, a commercial microchip for detection of rifampicin resistance in Mycobacterium tuberculosis was used. Hybridization of a 126 nt long single-stranded DNA (ssDNA) fragment of the rpoB gene according to manufacturer's protocol has been compared to hybridization of the same double-stranded DNA (dsDNA) fragment using the developed approach. Hybridization signals obtained by both methods were comparable in intensity and correlated closely. Second, a 22 nt long hairpin-forming oligonucleotide was designed and hybridized with a custom microchip containing probes complementary to both strands of the oligonucleotide. Conventional hybridization of this oligonucleotide did not yield any significant signals. Cleavage of the hairpin loop resulted in the formation of a 9 bp long intermolecular duplex. Hybridization of the duplex using the suggested technique yielded strong signals. The proposed approach allows analyzing target DNA in double-stranded form bypassing the preparation of single-stranded targets. Moreover, both complementary chains could be analyzed simultaneously, providing a reliable internal control. Being combined with fragmentation this method opens new possibilities in analyzing ssDNA with complex secondary structure.

Kinetic effects on signal normalization in oligonucleotide microchips with labeled immobilized probes

Among various factors affecting operation of oligonucleotide microchips, the variations in concentration and in homogeneous distribution of immobilized probes over the cells are one of the most important. The labeling of immobilized probes ensures the complete current monitoring on the probe distribution and is reliable and convenient. Using hydrogel-based oligonucleotide microchips, the applicability of Cy3-labeled immobilized probes for quality control and signal normalization after hybridization with Cy5-labeled target DNA was investigated. This study showed that proper signal normalization should be different in thermodynamic conditions and in transient regime with hybridization far from saturation. This kinetic effect holds for both hydrogel-based and surface oligonucleotide microchips. Besides proving basic features, the technique was assessed on a sampling batch of 50 microchips developed for identifying mutations responsible for rifampicin and isoniazid resistance of Mycobacterium tuberculosis.

High-level rifampin resistance correlates with multiple mutations in the rpoB gene of pulmonary tuberculosis isolates from the Afghanistan border of Iran

The aim of this study was to investigate the significance of multiple mutations in the rpoB gene as well as predominant nucleotide changes and their correlation with high levels of resistance to rifampin (rifampicin) in Mycobacterium tuberculosis isolates that were randomly collected from the sputa of 46 patients with primary and secondary cases of active pulmonary tuberculosis from the southern region (Afghanistan border) of Iran where tuberculosis is endemic. Drug susceptibility testing was performed using the CDC standard conventional proportional method. DNA extraction, rpoB gene amplification, and DNA sequencing analysis were performed. Thirty-five (76.09%) isolates were found to have multiple mutations (two to four) in the rpoB (beta-subunit) gene. Furthermore, we demonstrate that the combination of mutations with more prevalent nucleotide changes were observed in codons 523, 526, and 531, indicating higher frequencies of mutations among patients with secondary infection. In this study, 76.08% (n = 35) of all isolates found to have mutation combinations involving nucleotide changes in codons 523 (GGG-->GCG), 531 (TCG-->TTG or TTC), and 526 (CAC-->CGC, TTC, AAC, or CAA) demonstrated an association with higher levels of resistance to rifampin (MIC, >or=100 microg/ml).

Diagnostic microarrays in hematologic oncology: applications of high- and low-density arrays

Microarrays have become important tools for high-throughput analysis of gene expression, chromosome aberrations, and gene mutations in cancer cells. In addition to high-density experimental microarrays, low-density, gel-based biochip technology represents a versatile platform for translation of research into clinical practice. Gel-based microarrays (biochips) consist of nanoliter gel drops on a hydrophobic surface with different immobilized biopolymers (primarily nucleic acids and proteins). Because of the high immobilization capacity of the gel, such biochips have a high probe concentration and high levels of fluorescence signals after hybridization, which allow the use of simple, portable detection systems. The notable accuracy of the analysis is reached as a result of the high level of discrimination between positive and negative gel-bound probes. Different applications of biochips in the field of hematologic oncology include analysis of chromosomal translocations in leukemias, diagnostics of T-cell lymphomas, and pharmacogenetics.

Multicenter evaluation of Bactec MGIT 960 system for second-line drug susceptibility testing of Mycobacterium tuberculosis complex

The Bactec MGIT 960 system for testing susceptibility to second-line drugs was evaluated with 117 clinical strains in a multicenter study. The four drugs studied were levofloxacin, amikacin, capreomycin, and ethionamide. The critical concentration established for levofloxacin and amikacin was 1.5 microg/ml, that established for capreomycin was 3.0 microg/ml, and that established for ethionamide was 5.0 microg/ml. The overall level of agreement between the agar proportion method and the MGIT 960 system was 96.4%, and the levels of agreement for the individuals drugs were 99.1% for levofloxacin, 100% for amikacin, 97.4% for capreomycin, and 88.9% for ethionamide. The rate of reproducibility of the drug susceptibility testing results between the participating laboratories was 99.5%.

Oligonucleotide microchip for subtyping of influenza A virus

BACKGROUND

Influenza A viruses are classified into subtypes depending on the antigenic properties of their two outer glycoproteins, hemagglutinin (HA) and neuraminidase (NA). Sixteen subtypes of HA and nine of NA are known. Lately, the circulation of some subtypes (H7N7, H5N1) has been closely watched because of the epidemiological threat they present.

OBJECTIVES

This study assesses the potential of using gel-based microchip technology for fast and sensitive molecular subtyping of the influenza A virus.

METHODS

The method employs a microchip of 3D gel-based elements containing immobilized probes. Segments of the HA and NA genes are amplified using multiplex RT-PCR and then hybridized with the microchip.

RESULTS

The developed microchip was validated using a panel of 21 known reference strains of influenza virus. Selected strains represented different HA and NA subtypes derived from avian, swine and human hosts. The whole procedure takes 10 hours and enables one to identify 15 subtypes of HA and two subtypes of NA. Forty-one clinical samples isolated during the poultry fall in Novosibirsk (Russia, 2005) were successfully identified using the proposed technique. The sensitivity and specificity of the method were 76% and 100%, respectively, compared with the 'gold standard' techniques (virus isolation with following characterization by immunoassay).

CONCLUSIONS

We conclude that the method of subtyping using gel-based microchips is a promising approach for fast detection and identification of influenza A, which may greatly improve its monitoring.

Genetic evaluation of relationship between mutations in rpoB and resistance of Mycobacterium tuberculosis to rifampin

Background

Rifampin is a first line antituberculosis drug active against bacilli in logarithmic and stationary phase, which interferes with RNA synthesis by binding to bacterial RNA polymerase. Tubercle bacilli achieve resistance to rifampin by accumulation of mutations in a short-81 bp region of the rpoB gene. Among many mutations identified in the rpoB gene, few were verified by molecular genetic methods as responsible for resistance to rifampin (RMP).

Results

In this study eight different mutations identified in an 81 bp section of a "hot spot" region of the rpoB gene of RMP resistant Mycobacterium tuberculosis clinical strains were evaluated in respect to drug resistance. It was found that: mutations in positions 526 (H/D), 516 (D/V) and 531 (S/L) result in high level resistance to rifampin; mutations in positions 516 (D/Y), 515 (M/I), 510 (Q/H) or a double mutation in codons 512 (S/I) and 516 (D/G) relate to low level of resistance. Gene rpoB carrying mutations in codon 513 (Q/L) introduced into an M. tuberculosis laboratory strain did not cause resistance to rifampin, however the same gene introduced into two different clinical strains did, with the level of resistance depending on the host strain.

Conclusion

Mutations in an 81 bp "hot spot" region of the rpoB of M. tuberculosis lead to different levels of resistance to rifampin. Some mutations in this "hot spot" region of rpoB require a specific genetic background for the host strain to develop resistance to rifampin. Therefore, the identification of such mutations in a clinical M. tuberculosis strain is not enough to classify the given strain as resistant to rifampin.

DNA microarrays in the clinic: infectious diseases

We argue that the most-promising area of clinical application of microarrays in the foreseeable future is the diagnostics and monitoring of infectious diseases. Microarrays for the detection and characterization of human pathogens have already found their way into clinical practice in some countries. After discussing the persistent, yet often underestimated, importance of infectious diseases for public health, we consider the technologies that are best suited for the detection and clinical investigation of pathogens. Clinical application of microarray technologies for the detection of mycobacteria, Bacillus anthracis, HIV, hepatitis and influenza viruses, and other major pathogens, as well as the analysis of their drug-resistance patterns, illustrate our main thesis.

Detection of antimicrobial resistance genes of pathogenic Salmonella from swine with DNA microarray

A glass-based microarray was developed to detect 11 antimicrobial resistance genes that confer resistance to aminoglycosides, tetracyclines, sulfonamides, and chloramphenicols. The target genes for microarray were generated from Salmonella isolates by PCR and confirmed by sequencing. The specificity of the microarray was tested using 11 positive DNA probes. The sensitivity was tested with tetA gene and Salmonella isolates. Using detection threshold of signal-to-noise ratio (S/N) > or = 1.5 or median pixel intensity > or =1000, antimicrobial resistance genes carried by 30 Salmonella isolates were detected. Common genes included sul I(76.7%, 23/30), aph(3')-IIa (60%, 18/30), tetC (60%, 18/30), cat] (43.3%, 13/30), tetA (40%, 12/30) and aadA1 (36.7%, 11/30), and the results were confirmed to be correct by PCR.

Phase variation and microevolution at homopolymeric tracts in Bordetella pertussis

BACKGROUND

Bordetella pertussis, the causative agent of whooping cough, is a highly clonal pathogen of the respiratory tract. Its lack of genetic diversity, relative to many bacterial pathogens, could limit its ability to adapt to a hostile and changing host environment. This limitation might be overcome by phase variation, as observed for other mucosal pathogens. One of the most common mechanisms of phase variation is reversible expansion or contraction of homopolymeric tracts (HPTs).

RESULTS

The genomes of B. pertussis and the two closely related species, B. bronchiseptica and B. parapertussis, were screened for homopolymeric tracts longer than expected on the basis of chance, given their nucleotide compositions. Sixty-nine such HPTs were found in total among the three genomes, 74% of which were polymorphic among the three species. Nine HPTs were genotyped in a collection of 90 geographically and temporally diverse B. pertussis strains using the polymerase chain reaction/ligase detection reaction (PCR/LDR) assay. Six HPTs were polymorphic in this collection of B. pertussis strains. Of note, one of these polymorphic HPTs was found in the fimX promoter, where a single base insertion variant was present in seven strains, all of which were isolated prior to introduction of the pertussis vaccine. Transcript abundance of fimX was found to be 3.8-fold lower in strains carrying the longer allele. HPTs in three other genes, tcfA, bapC, and BP3651, varied widely in composition across the strain collection and displayed allelic polymorphism within single cultures.

CONCLUSION

Allelic polymorphism at homopolymeric tracts is common within the B. pertussis genome. Phase variability may be an important mechanism in B. pertussis for evasion of the immune system and adaptation to different niches in the human host. High sensitivity and specificity make the PCR/LDR assay a powerful tool for investigating allelic variation at HPTs. Using this method, allelic diversity and phase variation were demonstrated at several B. pertussis loci.

Molecular characteristics of rifampicin- and isoniazid-resistant Mycobacterium tuberculosis isolates from the Russian Federation

OBJECTIVES

Three Mycobacterium tuberculosis genetic loci--rpoB and katG genes and the fabG1(mabA)-inhA operon promoter region--were studied to reveal the mutations associated with rifampicin and isoniazid resistance.

METHODS

Four hundred and twelve isolates of M. tuberculosis from different regions of the Russian Federation were collected during 1997-2005. A matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS)-based minisequencing method was used for the detection of mutations.

RESULTS

Thirteen different variants of single mutations in codons 533, 531, 526, 516, 513 and 511 of the rifampicin resistance-determining region of the rpoB gene as well as the TTG insertion in the 514a position were found among the rifampicin-resistant isolates. Single nucleotide substitutions in codons 531, 526 and 516 (64.8%, 10.3% and 7.7%, respectively) were the most prevalent mutations. Codon 526 was shown to be the most variable of all. No mutations were detected in rpoB genes for 29 (10.7%) of the rifampicin-resistant isolates. 76.9% of the isoniazid-resistant isolates carried single mutations in codon 315 of the katG gene. For another 12.9% of them, double mutations in the katG gene and the fabG1(mabA)-inhA promoter region were revealed. No mutations were detected in 8.2% of the isoniazid-resistant isolates.

CONCLUSIONS

Molecular analysis of the loci of rpoB and katG genes and the inhA promoter region of 412 M. tuberculosis clinical isolates from various parts of the Russian Federation was carried out. The new MALDI-TOF MS-based method may be used for rapid and accurate monitoring of the spread of drug resistance.

Molecular characterization of rpoB gene mutations in rifampicine-resistant Mycobacterium tuberculosis isolates from tuberculosis patients in Belarus

The aim of this study was to investigate the frequency, location and type of rpoB mutations in Mycobacterium tuberculosis isolated from patients in Belarus. Tuberculosis cases are increasing every year in Belarus. Moreover, resistance to anti-tuberculosis drugs, especially to rifampicine, has increased. In this study, 44 rifampicine-resistance M. tuberculosis clinical isolates (including multidrug-resistant isolates) were subjected to DNA sequencing analysis of the hypervariable region (hot-spot) of the rpoB gene originating from different geographical regions in Belarus. Sixteen different types of mutations were identified. The most common point mutations were in codons 510 (47.7%), 526 (45.5%), 523 (40.86%) and 531 (29.5%). Eleven isolates (27.7%) carried one mutation and 23 (52%), 7 (16%), 3 (7%) of isolates carried 2, 3 and 4 mutations, respectively. A characteristic, prominent finding of this study was high frequency of multiple mutations in different codons of the rpoB gene (27.7%) and also the detection of unusual types of mutations in the 510 codon, comprising CAG mutations (deletion or changing, to CTG, CAC or CAT). In our study, the change TTG in codon 531 was found in 92% of isolates and the change TGC in 8% of isolates. A TAC change in codon 526 was not found, but the GAC change was found in all isolates. Isolates of M. tuberculosis isolated in Belarus were characterized by the wide spectrum of the important mutations and might belong to the epidemic widespread clones.

Evaluation of the TB-Biochip oligonucleotide microarray system for rapid detection of rifampin resistance in Mycobacterium tuberculosis

The TB-Biochip oligonucleotide microarray system is a rapid system to detect mutations associated with rifampin (RIF) resistance in mycobacteria. After optimizing the system with 29 laboratory-generated rifampin-resistant mutants of Mycobacterium tuberculosis, we evaluated the performance of this test using 75 clinical isolates of Mycobacterium tuberculosis. With this small sample set, the TB-Biochip system displayed a sensitivity of 80% and a specificity of 100% relative to conventional drug susceptibility testing results for RIF resistance. For these samples (approximately 50% tested positive), the positive predictive value was 100% and the negative predictive value was 85%. Four of the seven observed discrepancies were attributed to rare and new mutations not represented in the microarray, while three of the strains with discrepant results did not carry mutations in the RIF resistance-determining region. The results of this study confirm the utility of the system for rapid detection of RIF resistance and suggest approaches to increasing its sensitivity.

Impact of prehybridization PCR amplification on microarray detection of nitrifying bacteria in wastewater treatment plant samples

A gel-based microarray that included a set of 26 oligonucleotide probes targeting all nitrifying bacteria at varying levels of specificity suggested the presence of targeted microorganisms when hybridized to RNA isolated from a wastewater treatment plant, but could not discriminate between perfectly matched and mismatched sequences due in part to low signal intensity. To enhance sensitivity and improve discrimination, polymerase chain reaction was used to selectively amplify the 16S rRNA genes of specific nitrifier groups. RNA transcribed from these DNA templates was hybridized to the microarray and thermal dissociation analysis was used to characterize the specificity of hybridization. Amplification with Nitrospira-specific primers resulted in the selective amplification of this target group, confirmed by both a significant increase in signal intensity and a melting profile identical to the reference RNA. In contrast, Nitrobacter was not detected in the environmental samples with probe Nbac1000 despite pre-amplification with Nitrobacter-specific primers, indicating the absence of strains containing this Nitrobacter-specific sequence. Pre-amplification using primers specific for beta-Proteobacterial ammonia-oxidizing bacteria resulted in a significant increase in signal intensity for probe Nso190, but melting profiles for probe Nso190 showed a slight deviation between amplified RNA and the reference microorganism, suggesting that the amplification products contained some sequences that varied by a single nucleotide difference in the probe target region.

LAB ON A CD

In this paper, centrifuge-based microfluidic platforms are reviewed and compared with other popular microfluidic propulsion methods. The underlying physical principles of centrifugal pumping in microfluidic systems are presented and the various centrifuge fluidic functions, such as valving, decanting, calibration, mixing, metering, heating, sample splitting, and separation, are introduced. Those fluidic functions have been combined with analytical measurement techniques, such as optical imaging, absorbance, and fluorescence spectroscopy and mass spectrometry, to make the centrifugal platform a powerful solution for medical and clinical diagnostics and high throughput screening (HTS) in drug discovery. Applications of a compact disc (CD)-based centrifuge platform analyzed in this review include two-point calibration of an optode-based ion sensor, an automated immunoassay platform, multiple parallel screening assays, and cellular-based assays. The use of modified commercial CD drives for high-resolution optical imaging is discussed as well. From a broader perspective, we compare technical barriers involved in applying microfluidics for sensing and diagnostic use and applying such techniques to HTS. The latter poses less challenges and explains why HTS products based on a CD fluidic platform are already commercially available, whereas we might have to wait longer to see commercial CD-based diagnostics.