Detection of human immunodeficiency virus type 1 antiretroviral resistance mutations by high-density DNA probe arrays

Electrochemical genosensing of Salmonella, Listeria and Escherichia coli on silica magnetic particles

A magneto-genosensing approach for the detection of the three most common pathogenic bacteria in food safety, such as Salmonella, Listeria and Escherichia coli is presented. The methodology is based on the detection of the tagged amplified DNA obtained by single-tagging PCR with a set of specific primers for each pathogen, followed by electrochemical magneto-genosensing on silica magnetic particles. A set of primers were selected for the amplification of the invA (278 bp), prfA (217 bp) and eaeA (151 bp) being one of the primers for each set tagged with fluorescein, biotin and digoxigenin coding for Salmonella enterica, Listeria monocytogenes and E. coli, respectively. The single-tagged amplicons were then immobilized on silica MPs based on the nucleic acid-binding properties of silica particles in the presence of the chaotropic agent as guanidinium thiocyanate. The assessment of the silica MPs as a platform for electrochemical magneto-genosensing is described, including the main parameters to selectively attach longer dsDNA fragments instead of shorter ssDNA primers based on their negative charge density of the sugar-phosphate backbone. This approach resulted to be a promising detection tool with sensing features of rapidity and sensitivity very suitable to be implemented on DNA biosensors and microfluidic platforms.

Next generation sequencing technologies

From the investigation of disease-associated loci in humans, to monitoring the changing genomes of pathogenic viruses and bacteria, sequencing is a powerful and versatile tool. A new generation of sequencing technologies will increase the speed and lower the cost of sequencing, and promises to expand the utility of sequencing in drug discovery and development.:

Use of molecular assays for the diagnosis of influenza

Respiratory infections are the third highest cause of death worldwide and influenza has the highest mortality rate among lower respiratory tract infections (LRTIs). Diagnosis of LRTIs relies mostly on clinical symptoms and is not fully satisfactory. Influenza laboratory diagnosis improves the efficiency of prophylaxis or treatment of influenza by antiviral molecules and has a strong impact on the cost-effectiveness of curative treatment. Inappropriate treatment of patients may result in spreading of resistant strains. Molecular diagnostics play a central role in the surveillance and response of pandemic influenza due to highly pathogenic strains. Real-time assays can be used for diagnosis or surveillance purposes in humans and animals, and microarrays can be used to identify and monitor the spread of dangerous variants. Molecular assays are also useful to identify and distinguish influenza, other respiratory viruses and bacteria, although their cost-effectiveness must be proven on a large scale. As new antiviral options will be available to clinicians, a better treatment choice will benefit the patient and community. Recent progress in molecular techniques will be reviewed. Examples of real-time assays for the detection of influenza viruses, including the highly pathogenic influenza A strains H5N1 and H7N7, will be discussed. Promising new techniques that allow detailed genotyping of viruses or multiplex detection of several respiratory pathogens from a unique specimen will also be discussed. These techniques will, in the near future, significantly improve the quality of diagnosis and surveillance of respiratory pathogens.

Magneto-capillary valve for integrated purification and enrichment of nucleic acids and proteins

We describe the magneto-capillary valve (MCV) technology, a flexible approach for integrated biological sample preparation within the concept of stationary microfluidics. Rather than moving liquids in a microfluidic device, discrete units of liquid are present at fixed positions in the device and magnetic particles are actuated between the fluids. The MCV concept is characterized by the use of two planar surfaces at a capillary mutual distance, with specific features to confine the fluids by capillary forces, and the use of a gas or a phase-change material separating the stationary aqueous liquids. We have studied the physics of magneto-capillary valving by quantifying the magnetic force as a function of time and position, which reveals the balance of magnetic, capillary and frictional forces in the system. By purification experiments with a fluorescent tracer we have measured the amount of co-transported liquid, which is a key parameter for efficient purification. To demonstrate the versatility of the technology, several MCV device architectures were tested in a series of biological assays, showing the purification and enrichment of nucleic acids and proteins. Target recovery comparable to non-miniaturized commercial kits was observed for the extraction of DNA from human cells in buffer, using a device architecture with patterned air valves. Experiments using an enrichment module and patterned air valves demonstrate a 40-fold effective enrichment of DNA in buffer. DNA was also successfully purified from blood plasma using paraffin phase-change valves. Finally, the enrichment of a protein biomarker (prostate-specific antigen) using geometrical air valves resulted in a 7-fold increase of detection signal. The MCV technology is versatile, offers extensive freedom for the design of fully integrated systems, and is expected to be manufacturable in a cost-effective way. We conclude that the MCV technology can become an important enabling technology for point-of-care systems with sample in-result out performance.

Application of nanomaterials to arrays for infectious disease diagnosis

As our understanding of infectious agents increases it has become possible to identify the biological components of individual strains with greater accuracy. This ability is aiding clinical microbiologists to control both existing and emerging infectious disease problems. Microarray technologies are playing an increasingly important role in supplying relevant test data. Control of the nanoscale structures of the materials used in arrays, including the supports, reagents and analytes, is now essential. New techniques for the manufacture of nanostructured supports is now allowing rapid advances in the fields of multianalyte testing and high-volume DNA sequencing.

Absence of genotypic drug resistance and presence of several naturally occurring polymorphisms of human immunodeficiency virus-1 CRF06_cpx in treatment-naive patients in Estonia

All non-B HIV-1 subtypes and circulating recombinant forms (CRFs) are characterized by several polymorphisms in protease (PR) region. In addition, in recent years the increasing use of antiretroviral treatment (ART) has rapidly raised the spread of transmitted drug resistance. We aimed to determine the presence of naturally occurring polymorphisms and transmitted drug resistance mutations (DRMs) in ART naïve HIV-1-positive subjects in Estonia. A total of 115 drug-naive HIV-1-infected subjects (mean age 27 years; 70% male; 65% infected via intravenous drug use and 34% by heterosexual contact) were enrolled. Viral genomic RNA from plasma was directly sequenced in PR, revertase (RT), and envelope (env) regions. Phylogenetic analysis of RT and env regions revealed that 89% and 3% of sequenced viruses belonged to CRF06_cpx and subtype A1, respectively, and 6% were described as unique recombinants (signed A1-06) between CRF06_cpx and subtype A1 viruses. No primary DRMs were found in PR or RT regions indicating the absence of transmitted drug resistance. The most common polymorphisms in the PR region were K14R, M36I, H69K, and L89M seen in 96%, 100%, 99%, and 100%, respectively. The clinical relevance of these polymorphisms in terms of success of ART has to be monitored in future clinical studies.

Micro- and nanotechnology for viral detection

Since the identification of viruses at the start of the 20th century, detecting their presence has presented great challenges. In the past two decades, there has been significant progress in viral detection methods for clinical diagnosis and environmental monitoring. The earliest advances were in molecular biology and imaging techniques. Advances in microfabrication and nanotechnology have now begun to play an important role in viral detection, and improving the detection limit, operational simplicity, and cost-effectiveness of viral diagnostics. Here we provide an overview of recent advances, focusing especially on advances in simple, device-based approaches for viral detection.

Genotypic resistance testing in HIV by arrayed primer extension

The analysis of mutations that are associated with the occurrence of drug resistance is important for monitoring the antiretroviral therapy of patients infected with human immunodeficiency virus (HIV). Here, we describe the establishment and successful application of Arrayed Primer Extension (APEX) for genotypic resistance testing in HIV as a rapid and economical alternative to standard sequencing. The assay is based on an array of oligonucleotide primers that are immobilised via their 5'-ends. Upon hybridisation of template DNA, a primer extension reaction is performed in the presence of the four dideoxynucleotides, each labelled with a distinct fluorophore. The inserted label immediately indicates the sequence at the respective position. Any mutation changes the colour pattern. We designed a microarray for the analysis of 26 and 33 codons in the HIV protease and reverse transcriptase, respectively, which are of special interest with respect to drug resistance. The enormous genome variability of HIV represents a big challenge for genotypic resistance tests, which include a hybridisation step, both in terms of specificity and probe numbers. The use of degenerated oligonucleotides resulted in a significant reduction in the number of primers needed. For validation, DNA of 94 and 48 patients that exhibited resistance to inhibitors of HIV protease and reverse transcriptase, respectively, were analysed. The validation included HIV subtype B, prevalent in industrialised countries, as well as non-subtype B samples that are more common elsewhere.

Toward a new era in sequencing

Sequencing is a powerful tool that helps scientists in gaining new insights in many areas of medicine and biology. The electrophoresis-based Sanger method is currently the most popular sequencing technology and was the foundation stone of the human genome project. With the Sanger technique it became possible to sequence not only complete genomes, but also fragments of genomes. Nowadays, this standard method is very close to reach its limits.

Application of oligonucleotide arrays to high-content genetic analysis

The scope of single nucleotide polymorphism genotyping for genetic association studies has expanded recently from the use of relatively small numbers of candidate genes and markers, to include hypothesis-free, whole-genome approaches using hundreds of thousands of polymorphisms. The ability to perform such large-scale association studies has been dependant on the development of highly parallel and cost-effective genotyping platforms, of which those based on oligonucleotide arrays have proved to be the most scalable and widely adopted. It is to be expected that the new array-based genotyping methods will not only greatly expand the scope of genetic studies, but, as further content is added to arrays, will also form part of an integrated set of DNA, RNA and proteomic analyses enabling the detailed, multilayered study of complex disease-linked phenotypes.

The DNA-Chip technology as a new molecular tool for the detection of HBV mutants

Genetic variability of the Hepatitis B virus (HBV) strongly impacts the natural history of infection and the efficiency of diagnosis, vaccination and treatment. A genotypc assay able to provide genetic information on all HBV genes would be a very important tool for clinicians and epidemiologists. The DNA-Chip technology has proved to be powerful and convenient for the diagnosis of infectious diseases due to bacteria and viruses. We have designed a genotyping assay based on polymerase chain reaction and DNA-Chip for HBV Starting from a unique specimen, analysis of polymorphisms at 150 positions along the genome and 383 mutations is possible as well as the determination of the genotype. Preliminary experiments with plasmas from infected patients show that results obtained with this reagent are strongly correlated with those obtained with sequencing.

DNA probe array for the simultaneous identification of herpesviruses, enteroviruses, and flaviviruses

Viral infections of the central nervous system (CNS) are caused by a variety of viruses, namely, herpesviruses, enteroviruses, and flaviviruses. The similar clinical signs provoked by these viruses make the diagnosis difficult. We report on the simultaneous detection of these major CNS pathogens using amplification by PCR and detection of amplified products using DNA microarray technology. Consensus primers were used for the amplification of all members of each genus. Sequences specific for the identification of each virus species were selected from the sequence alignments of each target gene and were synthesized on a high-density microarray. The amplified products were pooled, labeled, and cleaved, followed by hybridization on a single array. This method was successfully used to identify herpesviruses, namely, herpes simplex virus type 1 (HSV-1), HSV-2, and cytomegalovirus; all serotypes of human enteroviruses; and five flaviviruses (West Nile virus, dengue viruses, and Langat virus). This approach, which used highly conserved consensus primers for amplification and specific sequences for identification, would be extremely useful for the detection of variants and would probably help solve some unexplained cases of encephalitis. The analytical sensitivity of the method was shown to be 500 genome equivalents ml(-1) for HSV-1, 0.3 50% tissue culture infectious doses (TCID50s) ml(-1) for the enterovirus coxsackievirus A9, and 200 TCID50s ml(-1) for West Nile virus. The clinical sensitivity of this method must now be evaluated.

Evaluation of a high-density oligonucleotide array for characterization of grlA, grlB, gyrA and gyrB mutations in fluoroquinolone resistant Staphylococcus aureus isolates

Using high-density oligonucleotide array technology, 30 Staphylococcus aureus strains were studied for the presence of mutations in genes involved in fluoroquinolone resistance: grlA, gyrA, grlB and gyrB. For the two most important genes, gyrA and grlA, correlation with sequencing reached 95.1%. If all genes were considered, correlation was 88.8%.

Prediction of HIV-1 Protease Inhibitor Resistance using a Protein–Inhibitor Flexible Docking Approach

Emergence of drug resistance remains one of the most challenging issues in the treatment of HIV-1 infection. Here we focus on resistance to HIV-1 protease inhibitors (PIs) at a molecular level, which can be analysed genotypically or phenotypically. Genotypic assays are based on the analysis of mutations associated with reduced drug susceptibility, but are problematic because of the numerous mutations and mutational patterns that confer drug resistance. Phenotypic resistance or susceptibility can be experimentally evaluated by measuring the amount of free drug bound to HIV-1 protease molecules, but this procedure is expensive and time-consuming. To overcome these problems, we have developed a docking protocol that takes protein–inhibitor flexibility into account to predict phenotypic drug resistance. For six FDA-approved PIs and a total of 1792 HIV-1 protease sequence mutants, we used a combination of inhibitor flexible docking and molecular dynamics (MD) simulations to calculate protein–inhibitor binding energies. Prediction results were expressed as fold changes of the calculated inhibitory constant ( Ki), and the samples predicted to have fold-increase in calculated Ki above the fixed cut-off were defined as drug resistant. Our combined docking and MD protocol achieved accuracies ranging from 72–83% in predicting resistance/susceptibility for five of the six drugs evaluated. Evaluating the method only on samples where our predictions concurred with established knowledge-based methods resulted in increased accuracies of 83–94% for the six drugs. The results suggest that a physics-based approach, which is readily applicable to any novel PI and/or mutant, can be used judiciously with knowledge-based approaches that require experimental training data to devise accurate models of HIV-1 PI resistance prediction.

Molecular diagnostics in virology

Molecular biology has significantly improved diagnosis in the field of clinical virology. Virus discovery and rapid implementation of diagnostic tests for newly discovered viruses has strongly beneficiated from the development of molecular techniques. Viral load and antiviral resistance or subtyping assays are now part of the biological monitoring of patients chronically infected by human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV) and CMV. It will be important to add to this panel assays for other viruses of the herpesviridae family. Qualitative assays for the detection of blood-borne viruses have increased safety of blood donation and organ transplantation. Screening of other blood-borne viruses (parvovirus B19, HAV), multiplexing of detection and test automation to improve practicability and reduce costs will be the next steps. A major evolution in the near future will be the generalization of NAT for the diagnosis of viral etiology in patients, mostly with respiratory, CNS or gastro-intestinal diseases. Major technical improvements have been made to avoid obstacles that still limit this generalization, i.e. genetic variability of viruses, multiplex detection, contamination risk. Commercial offers already exist but menus must be extended to limit the validation and documentation work associated with home-brew assays. Real-time amplification has allowed the development of new NAT platforms but automation and integration of all steps of the reaction are still required to reduce hands-on-time, time-to-result and costs, and to increase throughput.

Pharmacogenomic genotyping methodologies

“Personalized medicine” based on an individual’s genetic makeup is slowly becoming a reality as pharmacogenomics moves from the research setting to the clinical laboratory. Concordance studies between genotype and phenotype have shown that inherited mutations in several key drug-metabolizing enzymes, such as cytochrome P450 (