Multiple Cross Displacement Amplification Coupled With Nanoparticles-Based Lateral Flow Biosensor for Detection of Staphylococcus aureus and Identification of Methicillin-Resistant S. aureus

Nanotechnology-Based Strategies in Parasitic Disease Management: From Prevention to Diagnosis and Treatment

Parasitic infections are a major global health issue causing significant mortality and morbidity. Despite substantial advances in the diagnostics and treatment of these diseases, the currently available options fall far short of expectations. From diagnosis and treatment to prevention and control, nanotechnology-based techniques show promise as an alternative approach. Nanoparticles can be designed with specific properties to target parasites and deliver antiparasitic medications and vaccines. Nanoparticles such as liposomes, nanosuspensions, polymer-based nanoparticles, and solid lipid nanoparticles have been shown to overcome limitations such as limited bioavailability, poor cellular permeability, nonspecific distribution, and rapid drug elimination from the body. These nanoparticles also serve as nanobiosensors for the early detection and treatment of these diseases. This review aims to summarize the potential applications of nanoparticles in the prevention, diagnosis, and treatment of parasitic diseases such as leishmaniasis, malaria, and trypanosomiasis. It also discusses the advantages and disadvantages of these applications and their market values and highlights the need for further research in this field.

Updates on developing and applying biosensors for the detection of microorganisms, antimicrobial resistance genes and antibiotics: a scoping review

Background

The inappropriate use of antibiotics in clinical and non-clinical settings contributes to the increasing prevalence of multidrug-resistant microorganisms. Contemporary endeavours are focused on exploring novel technological methodologies, striving to create cost-effective and valuable alternatives for detecting microorganisms, antimicrobial resistance genes (ARGs), and/or antibiotics across diverse matrices. Within this context, there exists an increasingly pressing demand to consolidate insights into potential biosensors and their implications for public health in the battle against antimicrobial resistance (AMR).

Methods

A scoping review was carried out to map the research conducted on biosensors for the detection of microorganisms, ARGs and/or antibiotics in clinical and environmental samples. The Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist was used. Articles published from 1999 to November 2022 and indexed in the following databases were included: MEDLINE, EMBASE, Web of Science, BIOSIS Citation index, Derwent Innovations index, and KCI-Korean Journal.

Results

The 48 studies included in the scoping review described the development and/or validation of biosensors for the detection of microorganisms, ARGs and/or antibiotics. At its current stage, the detection of microorganisms and/or ARGs has focused primarily on the development and validation of biosensors in clinical and bacterial samples. By contrast, the detection of antibiotics has focused primarily on the development and validation of biosensors in environmental samples. Asides from target and samples, the intrinsic characteristics of biosensors described in the scoping review were heterogenous. Nonetheless, the number of studies assessing the efficacy and validation of the aforementioned biosensor remained limited, and there was also a lack of comparative analyses against conventional molecular techniques.

Conclusion

Promoting high-quality research is essential to facilitate the integration of biosensors as innovative technologies within the realm of public health challenges, such as antimicrobial resistance AMR. Adopting a One-Health approach, it becomes imperative to delve deeper into these promising and feasible technologies, exploring their potential across diverse sample sets and matrices.

Highly sensitive and rapid identification of coxsackievirus A16 based on reverse transcription multiple cross displacement amplification combined with nanoparticle-based lateral flow biosensor assay

Introduction

One of the main pathogens responsible for human hand, foot, and mouth disease (HFMD), coxsackievirus A16, has put young children’s health at danger, especially in countries in the Asia-Pacific region. Early quick identification is essential for the avoidance and control of the disorder since there are no vaccinations or antiviral medications available to prevent and manage CVA16 infection.

Methods

Here, we describe the creation of an easy, speedy, and accurate CVA16 infection detection approach using lateral flow biosensors (LFB) and reverse transcriptionmultiple cross displacement amplification (RT-MCDA). A group of 10 primers was developed for the RT-MCDA system in order to amplify the genes in an isothermal amplification device while targeting the highly conserved region of the CVA16 VP1 gene. Then, without requiring any extra tools, RT-MCDA amplification reaction products might well be detected by visual detection reagent (VDR) and LFB.

Results

The outcomes showed that 64°C within 40 min was the ideal reaction setting for the CVA16-MCDA test. Target sequences with <40 copies might be found using the CVA16-MCDA. There was no cross-reaction among CVA16 strains and other strains. The findings demonstrated that the CVA16-MCDA test could promptly and successfully identify all of the CVA16-positive (46/220) samples identified by the traditional real-time quantitative polymerase chain reaction (qRT-PCR) assays for 220 clinical anal swab samples. The whole process, such as the processing of the sample (15 min), the MCDA reaction (40 min), and the documenting of the results (2 min), could be finished in 1 h.

Conclusion

The CVA16-MCDA-LFB assay, which targeted the VP1 gene, was an efficient, simple, and highly specific examination that might be used extensively in rural regions’ basic healthcare institutions and point-of-care settings.

Development of a Multiplex Polymerase Chain Reaction-Based DNA Lateral Flow Assay as a Point-of-Care Diagnostic for Fast and Simultaneous Detection of MRSA and Vancomycin Resistance in Bacteremia

To reduce high mortality and morbidity rates, timely and proper treatment of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection is required. A multiplex polymerase reaction (mPCR)-based DNA lateral flow assay (MBDLFA) was developed as a point-of-care diagnostic for simultaneous identification of S. aureus, methicillin resistance, and vancomycin resistance directly from blood or blood cultures. A mPCR was developed to detect nuc, mecA, and vanA/B; its sensitivity, specificity, and limit of detection (LOD) were determined. The developed reaction was further modified for use in MBDLFA and its sensitivity for detection of target genes from artificially inoculated blood samples was checked. The optimized mPCR successfully detected nuc, mecA, and vanA/B from genomic DNA of bacterial colonies with LODs of 107, 107, and 105 CFU/mL, respectively. The reaction was sensitive and specific. The optimized mPCR was used in MBDLFA that detected nuc, mecA, and vanA/B with LODs of 107, 108, and 104 CFU/mL, respectively, directly from artificially inoculated blood. The developed MBDLFA can be used as a rapid, cheap point-of-care diagnostic for detecting S. aureus, MRSA, and vancomycin resistance directly from blood and blood cultures in ~2 h with the naked eye. This will reduce morbidity, mortality, and treatment cost in S. aureus bacteremia.

Real-time multiple cross displacement amplification assay for rapid and sensitive detection of Haemophilus influenzae

Haemophilus influenzae is an opportunistic pathogen usually causing bacteremia, meningitis, and pneumonia in children. Here, we developed a method based on multiple cross displacement amplification (MCDA) method and real-tme fluorescence technique for rapid detection of H. influenzae. A set of 10 primers was designed for the H. influenzae real-time MCDA reaction, and a core primer was modified with a restriction endonuclease recognition sequence, a fluorescent, and a quencher according to the principle of the real-time MCDA assay. The H. influenzae real-time MCDA reactions were performed using a fluorescence instrument at 63°C for 40 min. The H. influenzae real-time MCDA assay can specifically detect H. influenzae without any cross-reaction with other bacteria as our results confirmed. The sensitivity of our assay is as low as 10 CFU per reaction. To validate its feasibility, our assay was applied to 40 DNA extracted from sputum samples. The results obtained from H. influenzae real-time MCDA were compared with that of H. influenzae–loop-mediated isothermal amplification (H. influenzae-LAMP) and MCDA-based lateral flow biosensor (MCDA-LFB). The positive rate of the real-time MCDA assay was 62.5%, which was consistent with the H. influenzae-MCDA-LFB assay, but was more sensitive than H. influenzae-LAMP (57.5%). Furthermore, the H. influenzae real-time MCDA assay takes only 40 min, which was less than that of a traditional PCR test. Taken together, the H. influenzae real-time MCDA assay reported here offers a new and valuable diagnostic tool for the reliable and rapid detection of H. influenzae.

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

Development and Application of a Multiple Cross Displacement Amplification Combined With Nanoparticle-Based Lateral Flow Biosensor Assay to Detect Candida tropicalis

Candida tropicalis is an increasingly opportunistic pathogen that causes serious invasive candidiasis threatening a patient’s life. Traditional methods to detect C. tropicalis infection depends on time-consuming, culture-based gold-standard methods. So, we sought to establish a new method that could detect target pathogens quickly, accurately, and straightforwardly. Herein, a combination of multiple cross displacement amplification (MCDA) and lateral flow biosensors (LFB) was employed to detect C. tropicalis. In the MCDA system, 10 primers were designed to identify the specific genes of C. tropicalis and amplify the genes in an isothermal amplification device. Then, MCDA amplification reaction products could be identified visibly by color change, and all the amplification products would be tested by LFB with no special equipment. The results demonstrated that the optimal reaction condition of C. tropicalis-MCDA assay was 64°C within 30 min, and only 10 fg DNA was required in each reaction. No cross-reaction was found between C. tropicalis strains and non-C. tropicalis strains. For 300 sputum samples, the results showed that MCDA-LFB assay could rapidly and successfully detect all of the C. tropicalis-positive (28/300) samples detected by the gold-standard method. The entire procedure, including specimen processing (40 min), isothermal reaction (30 min) and result reporting (within 2 min), could be completed within 75 min. Briefly, the study results demonstrated that the detection ability of C. tropicalis-MCDA-LFB assay was better than culture methods with more simplicity, rapidity, sensitivity and specificity. Hence, MCDA-LFB strategy is an effective tool to rapidly detect C. tropicalis in clinical samples, especially in resource-poor areas.

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Are Nanobiosensors an Improved Solution for Diagnosis of Leishmania?

Leishmaniasis is one of the deadliest neglected tropical diseases affecting 12-15 million people worldwide, especially in middle- and low-income countries. Rapid and accurate diagnosis of the disease is important for its adequate management and treatment. Several techniques are available for the diagnosis of leishmaniasis. Among these, parasitological and immunological tests are most widely used. However, in most cases, the utilized diagnostic techniques are not good enough, showing cross-reactivity and reduced accuracy. In recent years, many new methods have been reported with potential for improved diagnosis. This review focuses on the diagnosis of Leishmania exploring the biosensors and nanotechnology-based options for their detection. New developments including the use of nanomaterials as fluorophores, fluorescence quenchers as reducing agents and as dendrimers for signal improvement and amplification, together with the use of aptamers to replace antibodies are described. Future research opportunities to overcome the current limitations on the available diagnostic approaches are also discussed.

Faster Detection of Staphylococcus aureus in Milk and Milk Powder by Flow Cytometry

A flow cytometry (FCM)-based method was developed for the faster detection of Staphylococcus aureus in milk and milk powder. Viable S. aureus cells were recognized by highly selective, fluorescently labeled antibodies and Propidium Iodide, and then analyzed by FCM. Using a 5-h pre-enrichment period, the method could detect low numbers of S. aureus cells in 6 h, with a limit of detection of 7.50 cells/mL in milk and 8.30 cells/g in milk powder. The established method was compared with the plate-based method using 75 ultra-high-temperature-treated milk samples, 25 pasteurized milk samples, 66 raw milk samples, and 123 milk powder samples. The two methods yielded similar results for the detection of the pathogen in all sample types. The FCM-based method allows effective and faster monitoring of S. aureus contamination and can be applied to the rapid detection of microorganisms in milk and dairy products.

Visual multiple cross displacement amplification for the rapid identification of S. agalactiae immediately from vaginal and rectal swabs

Streptococcus agalactiae (S. agalactiae) is an important pathogen that can lead to neonatus and mother infection. The current existing techniques for the identification of S. agalactiae are limited by accuracy, speed and high-cost. Therefore, a new multiple cross displacement amplification (MCDA) assay was developed for test of the target pathogen immediately from vaginal and rectal swabs. MCDA primers screening were conducted targeting S. agalactiae pcsB gene, and one set of MCDA primers with better rapidity and efficiency was selected for establishing the S. agalactiae-MCDA assay. As a result, the MCDA method could be completed at a constant temperature of 61 °C, without the requirement of special equipment. The detection limit is 250 fg (31.5 copies) per reaction, all S. agalactiae strains displayed positive results, but not for non-S. agalactiae strains. The visual MCDA assay detected 16 positive samples from 200 clinical specimen, which were also detected positive by enrichment/qPCR. While the CHROMagar culture detected 6 positive samples. Thus, the MCDA assay is prefer to enrichment/qPCR and culture for detecting S. agalactiae from clinical specimen. Particularly, the whole test of MCDA takes about 63.1 min, including sample collection (3 min), DNA preparation (15 min), MCDA reaction (45 min) and result reporting (6 s). In addition, the cost was very economic, with only US$ 4.9. These results indicated that our S. agalaciae-MCDA assay is a rapid, sensitive and cost-efficient technique for target pathogen detection, and is more suitable than conventional assays for an urgent detection, especially for 'on-site' laboratories and resource-constrained settings.

A diagnostic test that uses isothermal amplification and lateral flow detection sdaA can detect tuberculosis in 60 min

AIMS

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is now the leading cause of death from infectious disease, thus rapid diagnostic and screening techniques for TB are urgently needed.

METHODS AND RESULTS

Here, a detection of MTB using multiple cross displacement amplification coupling with nanoparticles-based lateral flow device (MCDA-LFD) was developed and validated, targeting the specific sdaA gene. The whole detection procedure, including rapid genomic DNA extraction (15 min), amplification (30 min) and result reporting (2 min), was completed within 50 min. No cross-reaction with non-mycobacteria and non-tuberculous mycobacteria (NTM) strains was observed. The sensitivity of sdaA-MCDA-LFD, Xpert MTB/RIF assay and culture results was 81·6, 48·3 and 37·9%, respectively, in TB patients. Among positive culture samples, the sensitivity of sdaA-MCDA-LFD and Xpert MTB/RIF assay was 93·9% (31/33) and 81·8% (27/33), respectively. Among culture-negative samples, the sensitivity of sdaA-MCDA-LFD and Xpert MTB/RIF assay was 74·1% (40/54) and 27·8% (15/54), respectively. The specificity of sdaA-MCDA-LFD and Xpert MTB/RIF was 95·4% (62/65) and 100% (65/65) in clinical samples from non-TB patients.

CONCLUSION

The sdaA-MCDA-LFD assay was a rapid, simple, specific and sensitive TB diagnostic test.

SIGNIFICANCE AND IMPACT OF THE STUDY

The sdaA-MCDA-LFD assay holds promise for application as a useful point-of-care test to detect MTB, and will play an important role in controlling and preventing TB.

Highly Sensitive and Rapid Identification of Streptococcus agalactiae Based on Multiple Cross Displacement Amplification Coupled With Lateral Flow Biosensor Assay

Streptococccus agalactiae (S. agalactiae) is an important neonatal pathogen that is associated with mortality and morbidity. Therefore, we developed a rapid, accurate, and sensitive method based on multiple cross displacement amplification (MCDA) for the detection of the target pathogen. Four sets of MCDA primers were designed for targeting the S. agalactiae-specific groEL gene, and one set of MCDA primers with the optimum amplification efficiency was screened for establishing the S. agalactiae-MCDA assay. As a result, the newly-developed assay could be conducted at a fixed temperature (61°C) for only 30 min, eliminating the use of complex instruments. A portable and user-friendly nanoparticle-based lateral flow biosensor (LFB) assay was employed for reporting MCDA results within 2 min. Our results suggested that the detection limit of the S. agalactiae-MCDA-LFB assay is 300 fg per reaction, and no cross-reaction occurred with non-S. agalactiae strains. For 260 vaginal and rectal swabs, the detection rate of the MCDA-LFB assay was 7.7%, which was in accordance with the reference method of enrichment/qPCR, and higher by 4.6% than the CHROMagar culture. Moreover, the total procedure time of the MCDA-LFB assay was around 50 min, including sample collection, template preparation, MCDA reaction, and result reporting. Therefore, the MCDA-LFB assay is superior to enrichment/qPCR and CHROMagar culture and has great promise for point-of-care testing of S. agalactiae from vaginal and rectal swabs of pregnant women in resource-limited settings.

Establishment and application of a multiple cross displacement amplification combined with nanoparticles-based biosensor method for the detection of Bordetella pertussis

Background

Bordetella pertussis is the causative agent of pertussis, a respiratory tract infectious disease.

Efficient techniques for detection of B. pertussis isolates are important for clinical diagnosis.

Multiple cross displacement amplification (MCDA), a novel isothermal amplification based molecular detection method, has been developed to overcome the technical drawback of the current methods in recent years. This aim of this study is to develop a MCDA with Nanoparticles-based Lateral Flow Biosensor (MCDA-LFB) for the detection of B. pertussis.

Results

A set of 10 primers based on the pertussis toxin (PT) promoter region sequence of B. pertussis was designed. The B. pertussis-MCDA-LFB assay was successfully established and optimized at 64 °C for reaction of 40 min. The detection limit was determined as 10 fg/reaction of pure DNA, and no cross-reactions to non-B. pertussis strains were observed, based on the specificity validation. The whole operation, ranging from template preparation to result reporting, could be completed within 70 min without requirement of costly equipment. The B. pertussis-MCDA-LFB in clinic sample detection yielded identical positive rates with traditional culture and showed higher sensitivity than conventional PCR. The results of MCDA-LFB are easier to read due to the usage of LFB.

Conclusions

The isothermal amplification based MCDA-LFB established in the present study is a specific, sensitive, rapid and economical technique for the detection of B. pertussis.

Current state of the art in rapid diagnostics for antimicrobial resistance

Antimicrobial resistance (AMR) is a fundamental global concern analogous to climate change threatening both public health and global development progress. Infections caused by antimicrobial-resistant pathogens pose serious threats to healthcare and human capital. If the increasing rate of AMR is left uncontrolled, it is estimated that it will lead to 10 million deaths annually by 2050. This global epidemic of AMR necessitates radical interdisciplinary solutions to better detect antimicrobial susceptibility and manage infections. Rapid diagnostics that can identify antimicrobial-resistant pathogens to assist clinicians and health workers in initiating appropriate treatment are critical for antimicrobial stewardship. In this review, we summarize different technologies applied for the development of rapid diagnostics for AMR and antimicrobial susceptibility testing (AST). We briefly describe the single-cell technologies that were developed to hasten the AST of infectious pathogens. Then, the different types of genotypic and phenotypic techniques and the commercially available rapid diagnostics for AMR are discussed in detail. We conclude by addressing the potential of current rapid diagnostic systems being developed as point-of-care (POC) diagnostic tools and the challenges to adapt them at the POC level. Overall, this review provides an insight into the current status of rapid and POC diagnostic systems for AMR.

Droplet digital polymerase chain reaction for rapid broad-spectrum detection of bloodstream infections

The droplet digital polymerase chain reaction (ddPCR) is a novel molecular technique that allows rapid quantification of rare target DNA sequences. Aim of this study was to explore the feasibility of the ddPCR technique to detect pathogen DNA in whole blood and to assess the diagnostic accuracy of ddPCR to detect bloodstream infections (BSIs), benchmarked against blood cultures. Broad-range primers and probes were designed to detect bacterial 16S rRNA (and Gram stain for differentiation) and fungal 28S rRNA. To determine the detection limit of ddPCR, 10-fold serial dilutions of E. coli and C. albicans were spiked in both PBS and whole blood. The diagnostic accuracy of ddPCR was tested in historically collected frozen blood samples from adult patients suspected of a BSI and compared with blood cultures. Analyses were independently performed by two research analysts. Outcomes included sensitivity and specificity of ddPCR. Within 4 h, blood samples were drawn, and DNA was isolated and analysed. The ddPCR detection limit was approximately 1-2 bacteria or fungi per ddPCR reaction. In total, 45 blood samples were collected from patients, of which 15 (33%) presented with positive blood cultures. The overall sensitivity of ddPCR was 80% (95% CI 52-96) and specificity 87% (95% CI 69-96). In conclusion, the ddPCR technique has considerable potential and is able to detect very low amounts of pathogen DNA in whole blood within 4 h. Currently, ddPCR has a reasonable sensitivity and specificity, but requires further optimization to make it more useful for clinical practice.

Simple, Rapid and Sensitive Detection of Pseudomonas aeruginesa by Colorimetric Multiple Cross Displacement Amplification

Pseudomonas aeruginosa (P. aeruginosa) is a major opportunistic pathogen in hospital-acquired infections. Thus, early diagnosis is the best strategy for fighting against these infections. In this report, we incorporated multiple cross displacement amplification (MCDA) combined with the malachite green (MG) for rapid, sensitive, specific and visual detection of P. aeruginosa by targeting the oprl gene. The MCDA-MG assay was conducted at 67°C for only 40 min during the amplification stage, and then products were directly detected by using colorimetric indicators (MG), eliminating the use of an electrophoresis instrument or amplicon analysis equipment. The entire process, including specimen processing (35 min), amplification (40 min) and detection (5 min), can be finished within 80 min. All 30 non-P. aeruginosa strains tested negative, indicating the high specificity of the MCDA primers. The analytical sensitivity of the MCDA-MG assay was 100 fg of genomic templates per reaction in pure culture, which was in complete accordance with MCDA by gel electrophoresis and real-time turbidity. The assay was also successfully applied to detecting P. aeruginosa in stool samples. Therefore, the rapidity, simplicity, and nearly equipment-free platform of the MCDA-MG technique make it possible for clinical diagnosis, and more.

Rapid and specific duplex detection of methicillin-resistant Staphylococcus aureus genes by surface-enhanced Raman spectroscopy

Methicillin-resistant Staphylococcus aureus (MRSA) is considered to be one of the important hospital-acquired pathogens. MRSA is also commonly associated with hospital-acquired infections and mortality. Quantitative and precise detection of MRSA is essential for rapid diagnosis and subsequent effective disease management strategies. We herein developed a highly specific method for rapid MRSA detection that combines surface-enhanced Raman spectroscopy (SERS) nanotags and polymerase chain reaction (PCR). SERS provided the sensitivity and spectral multiplexing capability while PCR provided the specificity required for the assay. The method was tested by the simultaneous detection of two MRSA specific genes (mecA and femA) amplified from genomic DNA isolated from clinical specimens. Magnetic isolation and rapid duplex detection were performed to obtain a detectable signal down to 10⁴ input copies within 80 min. This demonstrated the potential of the SERS-PCR based approach for the accurate identification of MRSA at an early-diagnosis stage. This study also provides an alternative approach to the existing methods for detecting clinical targets without compromising sensitivity and selectivity, and with minimal handling steps. We thus believe that this approach will find a broad application in clinical applications.

Current and Future Perspectives on Isothermal Nucleic Acid Amplification Technologies for Diagnosing Infections

Nucleic acid amplification technology (NAAT) has assumed a critical position in disease diagnosis in recent times and contributed significantly to healthcare. Application of these methods has resulted in a more sensitive, accurate and rapid diagnosis of infectious diseases than older traditional methods like culture-based identification. NAAT such as the polymerase chain reaction (PCR) is widely applied but seldom available to resource-limited settings. Isothermal amplification (IA) methods provide a rapid, sensitive, specific, simpler and less expensive procedure for detecting nucleic acid from samples. However, not all of these IA techniques find regular applications in infectious diseases diagnosis. Disease diagnosis and treatment could be improved, and the rapidly increasing problem of antimicrobial resistance reduced, with improvement, adaptation, and application of isothermal amplification methods in clinical settings, especially in developing countries. This review centres on some isothermal techniques that have found documented applications in infectious diseases diagnosis, highlighting their principles, development, strengths, setbacks and imminent potentials for use at points of care.

A Novel Detection of Enterococcus faecalis Using Multiple Cross Displacement Amplification Linked with Gold Nanoparticle Lateral Flow Biosensor

Background

Enterococcus faecalis, an opportunistic bacterial pathogen, is one of the most frequently isolated bacterial species and cause of serious nosocomial infections in recent decades. A reliable and rapid assay for E. faecalis detection is significant for the diagnosis and follow-up treatment.

Methods

A novel assay method, named multiple cross displacement amplification linked with nanoparticle-based lateral flow biosensor (MCDA-LFB), was applied for detecting E. faecalis strains. A set of special 10 primers was designed according to E. faecalis-specific gene Ef0027. The MCDA amplification conditions, including the target DNA concentration, reaction temperature and time, were optimized. The sensitivity and specificity of MCDA method were tested in the current study, and then, the MCDA-LFB technology was applied to detect the E. faecalis strain from clinical samples.

Results

The E. faecalis specific primers were valid for the establishment of MCDA-LFB technology forthe detection of E. faecalis based on the Ef0027 gene. The MCDA amplification condition was optimized at 62°C for 35 min. The MCDA products were directly sensed and displayed with a biosensor. The full process, comprising genomic DNA template preparation (approximately 30 mins), amplification of MCDA (35 mins), and the product identification (approximately 2 mins), could be achieved in 70 mins. The MCDA technique could detect as little as 10 fg per reaction system of pure E. faecalis genomic DNA. The specificity of E. faecalis-MCDA-LFB method is 100%, with no cross-reactions to non-E. faecalis strains.

Conclusion

The MCDA-LFB technique established in the present study is a reliable, simple, rapid, sensitive and specific method to assay E. faecalis and can be applied for the detection of clinical samples.

Development and Clinical Validation of Multiple Cross Displacement Amplification Combined With Nanoparticles-Based Biosensor for Detection of Mycobacterium tuberculosis: Preliminary Results

Tuberculosis is still a major threat to global public health. Here, a novel diagnosis assay, termed as multiple cross displacement amplification combined with nanoparticle-based lateral flow biosensor (MCDA-LFB), was developed to simultaneously detect IS6110 and IS1081 of Mycobacterium tuberculosis (MTB) in DNA extracted from reference strain H37Rv and clinical samples. The amplification can be finished within 30 min at a fixed temperature (67°C), thus the whole procedure, including rapid template preparation (15 min), isothermal reaction (30 min) and result reporting (2 min), can be completed within 50 min. The limit of detection of multiplex MCDA assay was 10 fg per reaction. By using the multiplex MCDA protocol, cross-reaction with non-mycobacteria and non-tuberculous mycobacteria (NTM) strains was not observed. Among clinically diagnosed TB patients, the sensitivity of liquid culture, Xpert MTB/RIF and multiplex MCDA assay was 42.0% (50/119), 49.6% (59/119), and 88.2% (105/119), respectively. Among culture positive samples, the sensitivity of Xpert MTB/RIF and multiplex MCDA assay was 86.0% (43/50) and 98.0% (49/50), respectively. Among culture negative samples, the sensitivity of Xpert MTB/RIF and multiplex MCDA assay was 23.2% (16/69) and 81.2% (56/69), respectively. The specificity was 100% (60/60) for Xpert MTB/RIF and 98.3% (59/60) for multiplex MCDA. Therefore, the multiplex MCDA assay for MTB detection is rapid, sensitive and easy to use and may be a promising test for early diagnosis of TB.

Enhanced antibiotic activity of ampicillin conjugated to gold nanoparticles on PEGylated rosette nanotubes

PURPOSE

This work presents the preparation of a nanocomposite of ampicillin-conjugated gold nanoparticles (AuNPs) and self-assembled rosette nanotubes (RNTs), and evaluates its antibacterial properties against two strains of drug-resistant bacteria (Staphylococcus aureus [S. aureus], methicillin-resistant S. aureus [MRSA]).

MATERIALS AND METHODS

Small, nearly monodisperse AuNPs (1.43±0.5 nm in diameter) nucleated on the surface of polyethylene glycol-functionalized RNTs in a one-pot reaction. Upon conjugation with ampicillin, their diameter increased to 1.86±0.32 nm. The antibacterial activity of the nanocomposite against S. aureus and MRSA was tested using different concentrations of ampicillin. The cytocompatibility of the nanocomposite was also tested against human dermal fibroblasts.

RESULTS

Based on bacterial inhibition studies, the nanocomposite demonstrated enhanced antibiotic activity against both bacterial strains. The minimum inhibitory concentration (MIC) of the nanocomposite against S. aureus was found to be 0.58 μg/mL, which was 18% lower than ampicillin alone. The nanocomposite also exhibited a 20 hrs MIC of 4 μg/mL against MRSA, approximately 10-20 times lower than previously reported values for ampicillin alone. In addition, at concentrations of 4 μg/mL of ampicillin (70 μg/mL of AuNPs), the nanocomposite showed negligible cytotoxic effects.

CONCLUSION

Our findings offer a new approach for the treatment of drug-resistant bacteria by potentiating inhibitory effects of existing antibiotics, and delivering them using a non-toxic formulation.

A novel isothermal amplification-based method for detection of Corynebacterium striatum

Corynebacterium striatum is an emerging multidrug-resistant pathogen causing increasing numbers of infections and nosocomial outbreaks worldwide. Thus, a simple, rapid and accurate method for C. striatum is urgently required for improving diagnosis efficiency. In this study, a C. striatum-multiple cross displacement amplification (MCDA) with visual detection reagent (VR) assay (C. striatum-MCDA-VR), which was a novel isothermal amplification-based method, was established to detect the species-specific ftr1 gene of C. striatum. Amplification was performed at a constant temperature (68 °C) for only 40 min, and the reaction results could be easily elucidated by observation of reaction mixture color when employing the VR. The limit of detection of this method was 10 fg of pure C. striatum DNA. No cross-reaction was observed with non-C. striatum strains. In testing of clinical sputum samples, the C. striatum-MCDA-VR assay showed excellent sensitivity and specificity when compared with sputum smear tests and PCR. The C. striatum-MCDA-VR assay is a simple, rapid and cost-effective approach for identifying C. striatum in microbiological laboratories, especially in resource-limited settings.

Multiple Cross Displacement Amplification Coupled With Gold Nanoparticles-Based Lateral Flow Biosensor for Detection of the Mobilized Colistin Resistance Gene mcr-1

Fast dissemination of the mobilized colistin resistance (mcr) gene mcr-1 in Enterobacteriaceae causes a huge threat to the treatment of severe infection. In the current report, a multiple cross displacement amplification (MCDA) coupled with the detection of amplified products by gold nanoparticles-based lateral flow biosensor (LFB) assay (MCDA-LFB) was established to identify the mcr-1 gene with simpleness, rapidity, specificity, and sensitivity. The MCDA-LFB assay was performed at a isothermal temperature (63°C) for only 30 min during the amplification stage, and the reaction products were directly identified by using LFB which obtained the result within 2 min. The entire process of experiments, from templates extraction to result judging, was accomplished in <60 min. For the analytical specificity of this method, all of the 16 mcr-1-producing strains were positive, and all of the non-mcr-1 isolates produced the negative results. The sensitivity of mcr-1-MCDA-LFB assay was as little as 600 fg of plasmid DNA per reaction in pure culture, and approximately 4.5 × 10³ CFU/mL (~4.5 CFU/reaction) in spiked fecal samples. Therefore, this technique established in the present study is suitable for the surveillance of mcr-1 gene in clinic and livestock industry.

Label-Free Cross-Priming Amplification Coupled With Endonuclease Restriction and Nanoparticles-Based Biosensor for Simultaneous Detection of Nucleic Acids and Prevention of Carryover Contamination

Here, we reported on a label-free cross-priming amplification (CPA) scheme that utilized endonuclease restriction for simultaneous detection of nucleic acids and elimination of carryover contamination. Reaction mixtures were detected in a nanoparticle-based lateral flow biosensor (LFB). The assay exhibited attractive traits in that it did not require the use of labeled primers or labeled probes, and thus, the technique could prevent undesired results arising from unwanted hybridization between labeled primers or between a probe and labeled primer. Isothermal amplification and endonuclease restriction digestion were conducted in a single pot, and the use of a closed-tube amplification removed false-positive results due to contaminants. To validate the assay's applicability, we employed the novel technique to detect the pathogen Staphylococcus aureus in pure cultures and artificial blood samples. The assay could detect target bacterium in pure culture with a 100 fg.μL^-1 detection limit, and in spiked blood samples with a 700 cfu.mL^-1 detection limit. The whole process, including sample procedure (20-min), isothermal amplification (60-min), endonuclease digestion (10-min) and result reporting (within 2-min), could be finished within 95-min. As a poof-of-concept assay, the technique devised in the current report could be employed for detecting various other sequences if the specific CPA primers were available.

Visual and rapid detection of Acinetobacter baumannii by a multiple cross displacement amplification combined with nanoparticles-based biosensor assay

The traditional microbiological methods used for detecting Acinetobacter baumannii were usually time-consuming and labor-intensive. Thus, we sought to establish a novel rapid detecting method for target pathogen. A set of multiple cross displacement amplification (MCDA) primers was designed to recognize 10 different regions of the pgaD gene, which was conservative and specific for the bacterium. In the MCDA system, amplification primers D1 and R1 were 5'-labeled with FITC (fluorescein) and biotin, respectively. Numerous FITC- and biotin-attached duplex amplicons were formed during the amplification stage, which were detected by nanoparticles-based lateral flow biosensors (LFB) through immunoreactions (FITC on the duplex and anti-FITC on the LFB test line) and biotin/streptavidin interaction (biotin on the duplex and streptavidin on the nanoparticles). The results showed that the optimized reaction condition of MCDA-LFB method was 62 °C within 25 min. There was no cross reaction with non-A. baumannii species and the non-Acinetobacter genera, and the detection limit for DNA samples was 100 fg/reaction. For 135 sputum samples, the detection results showed that the detection ability of MCDA-LFB assay was superior to the culture methods and conventional PCR. Therefore, MCDA-LFB assay could be a potential tool for the rapid detection of A. baumannii in clinical samples and low resource areas.

Nanomaterial-based optical and electrochemical techniques for detection of methicillin-resistant Staphylococcus aureus: a review

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for a number of life-threatening complications in humans. Mutations in the genetic sequence of S. aureus due to the presence of certain genes results in resistance against β-lactamases. Thus, there is an urgent need for developing highly sensitive techniques for the early detection of MRSA to counter the rise in resistant strains. This review (142 refs.) extensively covers literature reports on nanomaterial-based optical and electrochemical sensors from the year 1983 to date, with particularly emphasis on recent advances in electrochemical sensing (such as voltammetry and impedimetric) and optical sensing (such as colorimetry and fluorometry) techniques. Among the electrochemical methods, various nanomaterials were employed for the modification of electrodes. Whereas, in optical assays, formats such as enzyme linked immunosorbent assay, lateral flow assays or in optical fiber systems are common. In addition, novel sensing platforms are reported by applying advanced nanomaterials which include gold nanoparticles, nanotitania, graphene, graphene-oxide, cadmium telluride and related quantum dots, nanocomposites, upconversion nanoparticles and bacteriophages. Finally, closing remarks and an outlook conclude the review. Graphical abstract Schematic of the diversity of nanomaterial-based methods for detection of methicillin-resistant Staphylococcus aureus (MRSA). AuNPs: gold nanoparticles; QDs: quantum dots; PVL: Panton-Valentine leukocidin; mecA gene: mec-gene complex encoding methicillin resistance.

A simple lateral flow biosensor for rapid detection of lead(ii) ions based on G-quadruplex structure-switching

A novel strip biosensor equipped with a colorimetric card shows great promise for in-field Pb²⁺ detection.