Biology subjects

Verma, M. S.

Publications and source records attributed to Verma, M. S..

8 recordsLinked to original sources

bioRxiv2024

Propidium monoazide is unreliable for quantitative live-dead molecular assays

Propidium monoazide (PMA) is a dye that distinguishes between live and dead cells in molecular assays like Polymerase Chain Reaction (PCR). It works by cross-linking to the DNA of cells that have compromised membranes or extracellular DNA upon photoactivation, making the DNA inaccessible for amplification. Currently, PMA is used to detect viable pathogens and alleviate systemic bias in the microbiome analysis of samples using 16S rRNA gene sequencing. In these applications, treated samples consist of different amounts of dead bacteria and a range of bacterial strains, variables that can affect the performance of PMA and lead to inconsistent findings across various research studies. To evaluate the effectiveness of PMA, we used a sensitive qPCR assay and post-treatment sample concentration to determine PMA activity accurately under varying sample conditions. We report that PMA is unreliable for viability assays when the concentration and composition of the bacterial mixture are unknown. PMA is only suitable for qualitatively assessing viability in samples containing a known number of dead microbes or extracellular DNA.

bioengineering↗

bioRxiv2024

Design and development of a field-deployable water bath for loop-mediated isothermal amplification assay

Nucleic acid testing has become a prominent method for rapid microbial detection. Unlike polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP) is a simple method of nucleic acid amplification where the reaction can be performed at a constant temperature and the output provided in a colorimetric format. A transparent water bath is a desirable instrument to perform the heating and observe the visual results. However, existing methods of heating water are not convenient for loading and unloading the test samples. Here, we developed a field-deployable water bath--an isothermal heater called IsoHeat for short-which is solely dedicated to performing LAMP reactions and can heat the water up to 85{degrees}C. Using 3D-printing and laser-cutting technology, we fabricated different parts and mechanically assembled the parts to develop the entire device. Users can commence the heating by pressing the start button on the screen after entering the target temperature. Subsequently, the device heats up the water bath and maintains the target temperature through a PID algorithm-based control system. We demonstrate that IsoHeat can operate in environmental temperatures ranging from 5-33 {degrees}C and it can conduct LAMP reactions in liquid format as well as in paper-based devices. IsoHeat is more efficient and user-friendly compared to a commercially available immersion-heating device, which is often used to perform LAMP reactions. This newly developed device would be helpful to detect pathogens conveniently in the field (e.g., at point-of-care for human applications, on farms for plant and animal applications, and in production facilities for food safety applications).

bioengineering↗

bioRxiv2024

Real-time monitoring of attenuated cytomegalovirus using Raman spectroscopy allows non-destructive characterization during flow

Real-time monitoring of viral particles can have a crucial impact on vaccine manufacturing and can alleviate public health by supporting continuous supply. Spectroscopic methods such as Raman spectroscopy can provide rapid and non-invasive measurements. Here, we have developed a Raman spectroscopy-based tool to monitor the quality and quantity of viral particles in a continuous flow set-up. The attenuated human cytomegalovirus (CMV) is characterized across a wide range of concentrations (4.50 x 109 to 2.90 x 1011 particles/mL) and flow rates (100 {micro}m/s to 1000 {micro}m/s) within a square quartz capillary. This process analytical technology (PAT) tool enables the detection of viral particles even at high flow rates such as 1000 {micro}m/s. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and dynamic light scattering (DLS) demonstrated that the samples maintain their integrity even after laser exposure, reiterating the non-invasive nature of Raman spectroscopy. To the best of our knowledge, this is the first report on characterizing CMV particles using Raman spectroscopy. We have also demonstrated the limit of detection (LoD) (2.36 x 1010 particles/mL) for CMV particles in continuous flow (via the Raman spectroscopy method) by addressing the effect of flow rate, concentration, and integrity of samples. This technology could enhance our understanding of the quality control in bio-manufacturing processes required in vaccine production.

bioengineering↗

bioRxiv2024

Super-resolved protein imaging using bifunctional light-up aptamers

Efficient labeling methods for protein visualization with minimal tag size and appropriate photophysical properties are required for single-molecule localization microscopy (SMLM), providing insights into the organization and interactions of biomolecules in cells at the molecular level. Among the fluorescent light-up aptamers (FLAPs) originally developed for RNA imaging, RhoBAST stands out due to its remarkable brightness, photostability, fluorogenicity, and rapid exchange kinetics, enabling super-resolved imaging with high localization precision. Here, we expand the applicability of RhoBAST to protein imaging by fusing it to protein-binding aptamers. The versatility of such bifunctional aptamers is demonstrated by employing a variety of protein-binding DNA or RNA aptamers and different FLAPs. Moreover, fusing RhoBAST with the GFP-binding aptamer AP3 facilitates high- and super-resolution imaging of GFP-tagged proteins, which is particularly valuable in view of the widespread availability of plasmids and stable cell lines expressing proteins fused to GFP. The bifunctional aptamers compare favorably with standard antibody-based immunofluorescence protocols, as they are 7-fold smaller than antibody conjugates and exhibit higher bleaching-resistance. We demonstrate the effectiveness of our approach in super-resolution microscopy in secondary mammalian cell lines and primary neurons by RhoBAST-PAINT, an SMLM protein imaging technique that leverages the transient binding of the fluorogenic rhodamine dye SpyRho to RhoBAST.

biophysics↗

bioRxiv2023

A portable, easy-to-use paper-based biosensor for rapid in-field detection of fecal contamination on fresh produce farms

Laboratory-based nucleic acid amplification tests (NAATs) are highly sensitive and specific, but they require the transportation of samples to centralized testing facilities and have long turnaround times. During the Coronavirus Disease 2019 (COVID-19) pandemic, substantial advancement has been achieved with the development of paper-based point-of-care (POC) NAATs, offering features such as low cost, being easy to use, and providing rapid sample-to-answer times. Although most of the POC NAATs innovations target clinical settings, we have developed a portable, paper-based loop-mediated isothermal amplification (LAMP) testing platform for on-farm applications, capable of detecting Bacteroidales as a fecal contamination biomarker. Our integrated platform includes a drop generator, a heating and imaging unit, and paper-based biosensors, providing sensitive results (limit of detection 3 copies of Bacteroidales per cm2) within an hour of sample collection. We evaluated this integrated platform on a commercial lettuce farm with a concordance of 100% when compared to lab-based tests. Our integrated paper-based LAMP testing platform holds great promise as a reliable and convenient tool for on-site NAATs. We expect that this innovation will encourage the fresh produce industry to adopt NAATs as a complementary tool for decision-making in growing and harvesting. We also hope that our work can stimulate further research in the development of on-farm diagnostic tools for other agricultural applications, leading to improved food safety and technology innovation.

bioengineering↗

bioRxiv2023

Bacteroidales as a Fecal Contamination Indicator in Fresh Produce Industry: A Baseline Measurement

Foodborne outbreaks caused by fecal contamination of fresh produce represent a serious concern to public health and the economy. As the consumption of fresh produce increases, public health officials and organizations have pushed for improvements in food safety procedures and environmental assessments to reduce the risk of contamination. Visual inspections and the establishment of "buffer zones" between animal feeding operations and producing fields are the current best practices for environmental assessments. However, a generalized distance guideline and visual inspections may not be enough to account for all environmental risk variables. Here, we report a baseline measurement surveying the background Bacteroidales concentration, as a quantitative fecal contamination indicator, in Californias Salinas Valley. We collected a total of 1632 samples from two romaine lettuce commercial fields at the time of harvesting through two seasons in a year. The Bacteroidales concentration was very low (0 - 2.00 copies/cm2). Furthermore, we established a practical methodology for evaluating the risk of fecal contamination in a real-world setting, complementing the current environmental assessment practices. This method can identify site-specific risks and offer fresh produce stakeholders a more comprehensive understanding of their fields. We anticipate this work can encourage the use of Bacteroidales in the fresh produce industry to monitor fecal contamination and prevent future foodborne outbreaks.

bioengineering↗

bioRxiv2023

A drop dispenser for simplifying on-farm detection of foodborne pathogens

Rapid nucleic-acid biosensors are useful for on-farm detection of foodborne pathogens on fresh produce during pre-season and pre-harvest stages. Such tools aim to be user-friendly so that a producer could operate them in a few simple steps and detect multiple targets. Currently, an easy-to-use device for on-farm applications does not exist commercially. One of the bottlenecks is the delivery of a prescribed amount of sample to the reaction sites of the biosensor using a simple and precise approach. Here, we developed drop dispensers using 3D printing and a hydrophilic surface chemistry treatment to generate precise drops (DNA/bacterial samples) of a few micro-liters ([~]20 to [~]33 {micro}L). We tested multiple copies of these devices over time of repeated application to estimate their shelf-lives which is about one month. In addition to drop generation tests, we employed these devices in nucleic-acid testing. The tests used loop-mediated isothermal amplification (LAMP) to detect DNA or whole cells of Shiga-toxin-producing Escherichia coli O157:H7. These tests were performed to simulate the on-farm sample collection (using collection flags that we previously designed) and delivery using the drop dispensers. Our results showed that these devices performed similarly to standard commercial pipettors in LAMP assays, providing a limit of detection of 7.8x106 cell/mL for whole-cell detection. This drop dispenser will eventually be part of a user-friendly consumable kit that will enable performing LAMP assays by non-specialist users for a cost of USD 4 per test.

bioengineering↗

bioRxiv2023

Modelling complex growth profiles of Bacteroides fragilis and Escherichia coli on various carbohydrates in an anaerobic environment

Previously published models for microbial growth focus only on either death or growth and are unable to account for differently shaped growth curves. Currently, there is no model capable of incorporating combinations of microbial growth trends. This study creates a bacterial growth model that incorporates growth, death, lag, and tail phases as well as applies this model to the growth trends of Bacteroides fragilis and Escherichia coli on 13 different carbohydrate substances. Growth trends were collected by measuring the optical densities over 72 hours for either B. fragilis or E. coli in a chemically defined media supplemented by a mono- or disaccharide. The Digital Environment to Enable Data-driven Science (DEEDS) platform was utilized to parse data and apply the developed model to obtain parameter values. E. coli was found to grow on the chemically defined media alone while B. fragilis was unable to grow on it alone. E. coli growth was led by 10 mM concentration of substrates while B. fragilis growth was substrate dependent. Bacterial death only occurred for B. fragilis but was found to be dependent on concentration for the two most significant substrates. A singular model was developed that does not require prior knowledge of metabolomics and is capable of incorporating a combination of growth and death trends.

microbiology↗