Single fluorophore melting curve analysis for detection of hypervirulent Clostridium difficile.

This study demonstrates a novel detection assay able to identify and subtype strains of Clostridium difficile. Primers carefully designed for melting curve analysis amplify DNA from three C. difficile genes, tcdB, tcdC and cdtB, during quantitative (q)PCR. The tcdB gene allows for confirmation of organism presence, whilst the tcdC and cdtB genes allow for differentiation of virulence status, as deletions in the tcdC gene and the concurrent presence of the cdtB gene, which produces binary toxin, are associated with hypervirulence. Following qPCR, subtyping is then achieved by automated, inline melting curve analysis using only a single intercalating dye and verified by microchip electrophoresis. This assay represents a novel means of distinguishing between toxigenic and hypervirulent C. difficile strains NAP1/027/BI and 078 ribotype, which are highly prevalent hypervirulent strains in humans. This methodology can help rapidly detect and identify C. difficile strains that impose a significant health and economic burden in hospitals and other healthcare settings.

Simple perfusion apparatus for manipulation, tracking, and study of oocytes and embryos.

OBJECTIVE: To develop and implement a device and protocol for oocyte analysis at a single cell level. The device must be capable of high resolution imaging, temperature control, perfusion of media, drugs, sperm, and immunolabeling reagents all at defined flow rates. Each oocyte and resultant embryo must remain spatially separated and defined. DESIGN: Experimental laboratory study. SETTING: University and academic center for reproductive medicine. PATIENT(S)/ANIMAL(S): Women with eggs retrieved for intracytoplasmic sperm injection (ICSI) cycles, adult female FVBN and B6C3F1 mouse strains, sea stars. INTERVENTION(S): Real-time, longitudinal imaging of oocytes after fluorescent labeling, insemination, and viability tests. MAIN OUTCOME MEASURE(S): Cell and embryo viability, immunolabeling efficiency, live cell endocytosis quantification, precise metrics of fertilization, and embryonic development. RESULT(S): Single oocytes were longitudinally imaged after significant changes in media, markers, endocytosis quantification, and development, all with supreme control by microfluidics. Cells remained viable, enclosed, and separate for precision measurements, repeatability, and imaging. CONCLUSION(S): We engineered a simple device to load, visualize, experiment, and effectively record individual oocytes and embryos without loss of cells. Prolonged incubation capabilities provide longitudinal studies without need for transfer and potential loss of cells. This simple perfusion apparatus provides for careful, precise, and flexible handling of precious samples facilitating clinical IVF approaches.

A novel subtyping assay for detection of Clostridium difficile virulence genes.

This proof-of-concept study demonstrates the application of a novel nucleic acid detection platform to detect Clostridium difficile in subjects presenting with acute diarrheal symptoms. This method amplifies three genes associated with C. difficile infection, including genes and deletions (cdtB and tcdC) associated with hypervirulence attributed to the NAP1/027/BI strain. Amplification of DNA from the tcdB, tcdC, and cdtB genes was performed using a droplet-based sandwich platform with quantitative real-time PCR in microliter droplets to detect and identify the amplified fragments of DNA. The device and identification system are simple in design and can be integrated as a point-of-care test to help rapidly detect and identify C. difficile strains that pose significant health threats in hospitals and other health-care communities.

Microdroplet sandwich real-time rt-PCR for detection of pandemic and seasonal influenza subtypes.

As demonstrated by the recent 2012/2013 flu epidemic, the continual emergence of new viral strains highlights the need for accurate medical diagnostics in multiple community settings. If rapid, robust, and sensitive diagnostics for influenza subtyping were available, it would help identify epidemics, facilitate appropriate antiviral usage, decrease inappropriate antibiotic usage, and eliminate the extra cost of unnecessary laboratory testing and treatment. Here, we describe a droplet sandwich platform that can detect influenza subtypes using real-time reverse-transcription polymerase chain reaction (rtRT-PCR). Using clinical samples collected during the 2010/11 season, we effectively differentiate between H1N1p (swine pandemic), H1N1s (seasonal), and H3N2 with an overall assay sensitivity was 96%, with 100% specificity for each subtype. Additionally, we demonstrate the ability to detect viral loads as low as 10(4) copies/mL, which is two orders of magnitude lower than viral loads in typical infected patients. This platform performs diagnostics in a miniaturized format without sacrificing any sensitivity, and can thus be easily developed into devices which are ideal for small clinics and pharmacies.

Subtyping clinical specimens of influenza A virus by use of a simple method to amplify RNA targets.

This work presents the clinical application of a robust and unique approach for RNA amplification, called a simple method for amplifying RNA targets (SMART), for the detection and identification of subtypes of H1N1 pandemic, H1N1 seasonal, and H3N2 seasonal influenza virus. While all the existing amplification techniques rely on the diffusion of two molecules to complex RNA structures, the SMART achieves fast and efficient amplification via single-molecule diffusion. The SMART utilizes amplifiable single-stranded DNA (ssDNA) probes, which serve as reporter molecules for capturing specific viral RNA (vRNA) sequences and are subsequently separated on a microfluidic chip under zero-flow conditions. The probe amplification and detection are performed using an isothermal (41°C) amplification scheme via a modified version of nucleic acid sequence-based amplification (NASBA). In our study, 116 consecutive, deidentified, clinical nasopharyngeal swab samples were analyzed independently in a blinded fashion using the SMART, reverse transcription-PCR (RT-PCR), antigen (Ag) testing, and viral culture. The SMART was shown to have a limit of detection (LOD) of approximately 10(5) vRNA copies/ml, corresponding with a time-to-positivity (TTP) value of 70 min for real-time detection. The SMART correctly detected influenza virus in 98.3% of the samples with a subtyping accuracy of 95.7%. This work demonstrates that the SMART represents a highly accurate diagnostic platform for the detection and subtyping of influenza virus in clinical specimens and offers significant advantages over the current commercially available diagnostic tools.

Real-time droplet DNA amplification with a new tablet platform.

We present a novel droplet-based tablet platform for temporal polymerase chain reaction (PCR) in microliter droplets. The simple design of the device does not require extensive processing or external equipment, which allows for greater ease of use and integration as a point-of-care diagnostic. We demonstrate its functionality to perform both PCR and reverse-transcription PCR for λ phage DNA and H3 influenza RNA with ramp rates and cycle times consistent with traditional PCR thermal cyclers. We additionally investigate the effect of performing PCR in small volumes on the reaction performance by specifically examining adsorption of reagents at the oil/water interface. We determined that adsorption of Taq polymerase at the biphasic interface reduces yield and impairs reaction performance at standard concentrations. Thus, microdroplet PCR reactions require additional polymerase to achieve sufficient amplification and we project for applications utilizing nanodroplets or picodroplets like digital applications, even greater concentrations of polymerase are required to achieve desired results. Following the adsorption investigation, we evaluated the sensitivity of λ phage PCR on our platform to be less than 2.0 copies/µL with an efficiency of 104.4% and similar sensitivity for reverse-transcription PCR for influenza H3 RNA.