Highly-sensitive detection of Salmonella typhi in clinical blood samples by magnetic nanoparticle-based enrichment and in-situ measurement of isothermal amplification of nucleic acids

Naked-Eye Detection of LAMP-Produced Nucleic Acids in Saliva Using Chitosan-Capped AuNPs in a Single-Tube Assay

Loop-mediated isothermal amplification (LAMP) is a low-technology molecular assay that is highly adaptable to point-of-care (POC) applications. However, achieving sensitive naked-eye detection of the amplified target in a crude sample is challenging. Herein, we report a simple yet highly efficient and sensitive methodology for the colorimetric visualization of a single target copy in saliva using chitosan-capped gold nanoparticles (Chit-AuNPs) synthesized via a green chemistry approach. The presence or absence of free Chit in the Chit-AuNPs solution was shown to affect LAMP colorimetric detection oppositely: the observed stabilization in the negative samples and aggregation in the positive samples in the presence of free Chit were reversed in the case of neat Chit-AuNPs. The mechanism of the two assays was investigated and attributed to electrostatic and depletion effects exerted between the Chit-AuNPs, free Chit, and the solution components. The developed contamination-free, one-tube assay successfully amplified and detected down to 1-5 cfu of Salmonella and 10 copies of SARS-CoV-2 per reaction (25 μL) used, respectively, as model DNA and RNA targets in the presence of 20% saliva, making the method suitable for POC applications. Compared to the commonly used pH-sensitive dyes, Chit-AuNPs are shown to have an enhanced sensitivity toward naked-eye colorimetric observation owing to the direct detection of DNA amplicons. Thus, this is a simple, highly sensitive, fast, and versatile naked-eye detection methodology that could be coupled to any LAMP or RT-LAMP assay, avoiding the need of using complicated sample pretreatments and/or AuNPs long and laborious functionalization processes.

Surface plasmon resonance-based oligonucleotide biosensor for Salmonella Typhi detection

Due to high mortality rates, typhoid fever still is one of the major health problems in the world, particularly in developing countries. The lack of highly specific and sensitive diagnostic tests and the great resemblance of typhoid fever symptoms to other diseases made the false-negative diagnosis a major challenge in typhoid fever management. Hence, we decided to design a Surface Plasmon Resonance (SPR) based biosensor for specific detection of Salmonella typhi through DNA hybridization. The results showed that the 10 nM of the synthetic target sequence, as well as 1 nM of PCR product, were the lowest feasible detected concentrations by the designed biosensor. This genosensor was also found to significantly distinguish the complementary sequence with the accuracy of one base mismatch sequence. The surface of the chip can be regenerated with NaOH solution and used for consecutive diagnosis. Therefore, the function of the designed biosensor indicates its high potential for Salmonella typhi detection practice.

Immunological characterization of chitosan adjuvanted outer membrane proteins of Salmonella enterica serovar Typhi as multi-epitope typhoid vaccine candidate

BACKGROUND

Outer membrane proteins (OMPs) of Gram-negative bacteria have been known as potential vaccine targets due to their antigenic properties and host specificity. Here, we focused on the exploration of the immunogenic potential and protective efficacy of total OMPs of Salmonella enterica serovar Typhi due to their multi epitope properties, adjuvanted with nanoporous chitosan particles (NPCPs). The study was designed to extrapolate an effective, low cost prophylactic approach for typhoid fever being getting uncontrolled in Pakistan due to emergence of extensively drug resistant (XDR) strains.

METHODS & RESULTS

The OMPs of two S. Typhi variants (with and without Vi capsule) alone and with nanoporous chitosan particles as adjuvant were comparatively analyzed for immunogenic potential in mice. Adaptive immunity was evaluated by ELISA and relative quantification of cytokine gene expression (IL4, IL6, IL9, IL17, IL10, TNF, INF and PPIA as house keeping gene) using RT-qPCR. Statistical analysis was done using Welch's test. The protection was recorded by challenging the immunized mice with 50% ×LD50 of S. Typhi. The Vi + ve-OMPs of S. Typhi showed the most promising results by ELISA and significantly high expression of IL-6, IL-10 and IL-17 and 92.5% protective efficacy with no detectable side effects.

CONCLUSION

We can conclude that the OMPs of Vi + ve S. Typhi are the most promising candidates for future typhoid vaccines because of cost effective preparation without expensive purification steps and multi-epitope properties. Chitosan adjuvant may have applications for oral protein based vaccines but found less effective in injectable preparations.

Nanomedicine as a promising strategy for the theranostics of infectious diseases

Infectious diseases caused by bacteria, viruses, and fungi and their global spread pose a great threat to human health. The 2019 World Health Organization report predicted that infection-related mortality will be similar to cancer mortality by 2050. Particularly, the global cumulative numbers of the recent outbreak of coronavirus disease (COVID-19) have reached 110.7 million cases and over 2.4 million deaths as of February 23, 2021. Moreover, the crisis of these infectious diseases exposes the many problems of traditional diagnosis, treatment, and prevention, such as time-consuming and unselective detection methods, the emergence of drug-resistant bacteria, serious side effects, and poor drug delivery. There is an urgent need for rapid and sensitive diagnosis as well as high efficacy and low toxicity treatments. The emergence of nanomedicine has provided a promising strategy to greatly enhance detection methods and drug treatment efficacy. Owing to their unique optical, magnetic, and electrical properties, nanoparticles (NPs) have great potential for the fast and selective detection of bacteria, viruses, and fungi. NPs exhibit remarkable antibacterial activity by releasing reactive oxygen species and metal ions, exerting photothermal effects, and causing destruction of the cell membrane. Nano-based delivery systems can further improve drug permeability, reduce the side effects of drugs, and prolong systemic circulation time and drug half-life. Moreover, effective drugs against COVID-19 are still lacking. Recently, nanomedicine has shown great potential to accelerate the development of safe and novel anti-COVID-19 drugs. This article reviews the fundamental mechanisms and the latest developments in the treatment and diagnosis of bacteria, viruses, and fungi and discusses the challenges and perspectives in the application of nanomedicine.

Surface-enhanced Raman spectroscopy for comparison of serum samples of typhoid and tuberculosis patients of different stages

BACKGROUND

Surface-enhanced Raman spectroscopy (SERS) is a reliable tool for the identification and differentiation of two different human pathological conditions sharing the same symptomology, typhoid and tuberculosis (TB).

OBJECTIVES

To explore the potential of surface-enhanced Raman spectroscopy for differentiation of two different diseases showing the same symptoms and analysis by principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA).

METHODS

Serum samples of clinically diagnosed typhoid and tuberculosis infected individuals were analyzed and differentiated by SERS using silver nanoparticles (Ag NPs) as a SERS substrate. For this purpose, the collected serum samples were analyzed under the SERS instrument and unique SERS spectra of typhoid and tuberculosis were compared showing notable spectral differences in protein, lipid and carbohydrates features. Different stages of the diseased class of typhoid (Early acute and late acute stage) and tuberculosis (Pulmonary and extra-pulmonary stage) were compared with each other and with healthy human serum samples, which were significantly separated. Moreover, SERS data was analyzed using multivariate data analysis techniques including principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA) and differences were so prominent to observe.

RESULTS

SERS Spectral data of typhoid and tuberculosis showed clear differences and were significantly separated using PCA. SERS spectral data of both stages of typhoid and tuberculosis were separated according to 1st principle component. Moreover, by analyzing data using partial least square discriminate analysis, differentiation of two disease classes were considered more valid with a 100% value of sensitivity, specificity and accuracy.

CONCLUSION

SERS can be employed for identification and comparison of two different human pathological conditions sharing same symptomology.

Development of an immunoassay test system based on monoclonal antybodies and immunomagnetic particles for the detection of F. tularensis cells

Tularemia is an especially dangerous infection caused by the gram-negative bacterium Francisella tularensis. It belongs to natural focal infections, and therefore is under continuous control by quarantine services. When carrying out their activities they use a whole range of diagnostic tools. The objective of this research is to develop an enzyme immunoassay based on highly specific monoclonal antibodies and immunomagnetic particles for monitoring the tularemia pathogen. To produce hybridomas mice were immunized with cells of the vaccine strain F. tularensis subsp. holarctica 15 NIIEG. After cell fusion hybridomas were selected by a solid-phase enzyme immunoassay (ELISA) using lipopolysaccharide (LPS) of the tularemia microbe. As a result, two hybridomas, 1C2 and 3F5, were produced. MABs of the hybridomas were obtained by using BALB / c mice. The MABs were purified by sepharose A affinity chromatography and used for conjugation with magnetic particles, and for biotinylation followed by matching a pair for ELISA. The pair of IMPs and MABs 3F5 as well as biotinylated FB11-x MABs was the best in detecting tularemia cells. The use of this MAB pair in ELISA allowed the identification of 105 microbial cells/ml in a 4 ml sample and 5×103 microbial cells/ml in a 45ml sample. Interaction with F. tularensis subsp. novicida Utah112 cells was absent.

Classification of Salmonella enterica of the (Para-)Typhoid Fever Group by Fourier-Transform Infrared (FTIR) Spectroscopy

Typhoidal and para-typhoidal Salmonella are major causes of bacteraemia in resource-limited countries. Diagnostic alternatives to laborious and resource-demanding serotyping are essential. Fourier transform infrared spectroscopy (FTIRS) is a rapidly developing and simple bacterial typing technology. In this study, we assessed the discriminatory power of the FTIRS-based IR Biotyper (Bruker Daltonik GmbH, Bremen, Germany), for the rapid and reliable identification of biochemically confirmed typhoid and paratyphoid fever-associated Salmonella isolates. In total, 359 isolates, comprising 30 S. Typhi, 23 S. Paratyphi A, 23 S. Paratyphi B, and 7 S. Paratyphi C, respectively and other phylogenetically closely related Salmonella serovars belonging to the serogroups O:2, O:4, O:7 and O:9 were tested. The strains were derived from clinical, environmental and food samples collected at different European sites. Applying artificial neural networks, specific automated classifiers were built to discriminate typhoidal serovars from non-typhoidal serovars within each of the four serogroups. The accuracy of the classifiers was 99.9%, 87.0%, 99.5% and 99.0% for Salmonella Typhi, Salmonella Paratyphi A, B and Salmonella Paratyphi C, respectively. The IR Biotyper is a promising tool for fast and reliable detection of typhoidal Salmonella. Hence, IR biotyping may serve as a suitable alternative to conventional approaches for surveillance and diagnostic purposes.

Identification of aldehyde oxidase 3 as a binding protein for squid ink polysaccharides using magnetic nanoparticles

To explore the interactive molecules of squid ink polysaccharides (SIP) for further understanding the action mechanisms of SIP bio-function, this study prepared SIP binding proteins from mouse liver using superparamagnetic nanometer beads. Michaelis–Menten constant (K_m) was detected from a Lineweaver–Burk double reciprocal plot to assess effect of SIP on activity of aldehyde oxidase (AOX). Results showed that three proteins, AOX-3, regucalcin (RGN) and α1-antitrypsin (A1AT3) were separated from mouse liver by magnetic nanoparticles conjugated with SIP. Contents of AOX-3 were much more than RGN and A1AT3. SIP (0.5 mg mL⁻¹) reduced K_m value of aldehyde oxidase of mouse liver from 91.79 μmol L⁻¹ to 43.70 μmol L⁻¹.

Superparamagnetic nanometer beads bonding SIP was employed to pull down the binding protein from the liver of mouse, which was identified as aldehyde oxidase 3. By means of enzyme kinetics analysis, SIP was found to activate AOX3 enzyme activity.

Application of magnetic nanoparticles in nucleic acid detection

Nucleic acid is the main material for storing, copying, and transmitting genetic information. Gene sequencing is of great significance in DNA damage research, gene therapy, mutation analysis, bacterial infection, drug development, and clinical diagnosis. Gene detection has a wide range of applications, such as environmental, biomedical, pharmaceutical, agriculture and forensic medicine to name a few. Compared with Sanger sequencing, high-throughput sequencing technology has the advantages of larger output, high resolution, and low cost which greatly promotes the application of sequencing technology in life science research. Magnetic nanoparticles, as an important part of nanomaterials, have been widely used in various applications because of their good dispersion, high surface area, low cost, easy separation in buffer systems and signal detection. Based on the above, the application of magnetic nanoparticles in nucleic acid detection was reviewed.

Simultaneous and high sensitive detection of Salmonella typhi and Salmonella paratyphi a in human clinical blood samples using an affordable and portable device

Enteric fever is one of the leading causes of infection and subsequent fatality (greater than 1.8 million) (WHO 2018), especially in the developing countries due to contaminated water and food inter twinned with unhygienic practices. Clinical gold standard technique of culture-based method followed by biochemical tests demand 72+ hours for diagnosis while newly developed techniques (like PCR, RT-PCR, DNA microarray etc.) suffer from high limit of detection or involve high-cost infrastructure or both. In this work, a quick and highly specific method, SMOL was established for simultaneous detection of Salmonella paratyphi A and Salmonella typhi in clinical blood samples. SMOL consists of (i) pre-concentration of S. typhi and S. paratyphi A cells using magnetic nanoparticles followed by (ii) cell lysis and DNA extraction (iii) amplification of select nucleic acids by LAMP technique and (iv) detection of amplified nucleic acids using an affordable portable device (costs less than $70). To identify the viability of target cells at lower concentrations, the samples were processed at two different time periods of t = 0 and t = 4 h. Primers specific for the SPA2539 gene in S. paratyphi A and STY2879 gene in S. typhi were used for LAMP. Within 6 h SMOL was able to detect positive and negative samples from 55 human clinical blood culture samples and detect the viability of the cells. The results were concordant with culture and biochemical tests as well as by qPCR. Statistical power analysis yielded 100%. SMOL results were concordant with culture and biochemical tests as well as by qPCR. The sensitive and affordable system SMOL will be effective for poor resource settings.