Rapid detection of foodborne pathogen Listeria monocytogenes by strand exchange amplification

Sensitive Methods to Detect Single-Stranded Nucleic Acids of Food Pathogens Based on Cell-Free Protein Synthesis and Retroreflection Signal Detection

Cell-free protein synthesis (CFPS) has recently gained considerable attention as a new platform for developing methods to detect various molecules, ranging from small chemicals to biological macromolecules. Retroreflection has been used as an alternative signal to develop analytical methods because it can be detected by using a simple instrument comprising a white light source and a camera. Here, we report a novel reporter protein that couples the capability of CFPS and the simplicity of retroreflection signal detection. The design of the reporter was based on two pairs of protein-peptide interactions, SpyCatcher003-SpyTag003 and MDM2-PMI(N8A). MDM2-MDM2-SpyCatcher003 was decided as the reporter protein, and the two peptides, SpyTag003 and PMI(N8A), were immobilized on the surfaces of retroreflective Janus particles and microfluidic chips, respectively. The developed retroreflection signal detection system was combined with a previously reported CFPS reaction that can transduce the presence of a single-stranded nucleic acid into protein synthesis. The resulting methods were applied to detect 16S rRNAs of several foodborne pathogens. Concentration-dependent relationships were observed over a range of 10° fM to 102 pM, with the limits of detection being single-digit femtomolar concentrations. Considering the designability of the CFPS system for other targets, the retroreflection signal detection method will enable the development of novel methods to detect various molecules.

Diverse methods of reducing and confirming false-positive results of loop-mediated isothermal amplification assays: A review

Loop-mediated isothermal amplification (LAMP), a rapid and sensitive isothermal nucleic acid amplification method, is a promising alternative to other molecular amplification techniques due to its superior specificity and sensitivity. However, due to primer dimerization, LAMP results in nonspecific and nontemplate amplification. And during the amplification confirmation process, there is carry-over contamination. These factors can result in false-positive results that overestimate the amount of DNA, preventing accurate detection. This review outlined several techniques for reducing false-positive LAMP results before amplification and confirming false-positive results after amplification. Before the amplification step, DNA polymerase activity can be decreased with organic additives such as dimethyl sulfoxide, betaine, and pullulan to prevent nonspecific amplification. The enzyme uracil-DNA-glycosylase (UDG) can eliminate false-positive results caused by carry-over contamination, and the hot-start effect with gold nanoparticles can reduce nonspecific amplification. When confirming false-positive results using clustered regularly interspaced short palindromic repeats, guide RNA accurately detects LAMP amplification, allowing differentiation from nonspecific amplification. By confirming amplification, the colorimetric change in the deoxyribozyme (DNAzyme) formed by the reaction of the G-quadruplex sequence of the LAMP amplicon and hemin can distinguish false-positive results. Lateral flow immunoassay can distinguish false-positive results by accurately recognizing hybridized probes to LAMP amplicons.

Amino-modified silica membrane capable of DNA extraction and enrichment for facilitated isothermal amplification detection of Mycoplasma pneumoniae

Herein, we developed a facile integrated Mycoplasma pneumoniae diagnosis platform by combining amino-modified silica membrane (AMSM)-based nucleic acids fast extraction and enrichment with colorimetric isothermal amplification detection. AMSM demonstrates a strong ability to capture and enrich nucleic acids in complicated biological matrices, and the purified AMSM/nucleic acids composite could be directly used to perform isothermal amplification including denaturation bubble-mediated strand exchange amplification (SEA) and loop-mediated isothermal amplification (LAMP) reactions. Through comparing clinical specimens, excellent performance of AMSM-based SEA assay with 93.33% sensitivity and 100% specificity relative to real-time PCR was observed, and for AMSM-based LAMP was 96.67% and 100%, respectively. The diagnostic procedure could be completed within 55 min, and the colorimetric-based visual result further alleviates the use of sophisticated equipment. The proposed approach possesses great potential as a simple and time-saving alternative for point-of-care testing (POCT) of M. pneumoniae in resource-limited regions.

Graphene oxide-assisted optimized narrow-thermal-cycling amplification for accurate detection of Salmonella spp

Salmonella is a rod-shaped, Gram-negative zoonotic pathogen that poses a serious global socioeconomic and public health threat. Rapid and accurate detection of Salmonella spp. is critical for effective control of its infection. In this study, an accurate, sensitive and specific graphene oxide-assisted accelerated strand exchange amplification (GO-ASEA) method for rapid detection of Salmonella spp. was developed and validated. The detection limit of the GO-ASEA method was 8.6 × 10¹ fg μL^-1 of Salmonella genomic DNA or 1 × 10¹ CFU g^-1 of Salmonella in spiked chicken faeces free of pre-enrichment. And the GO-ASEA method could specifically detect Salmonella spp. without cross-reactivity with other enteric pathogens. In addition, the novel method achieved Salmonella detection within 30 min and was validated using 209 clinical samples, showing its good clinical applicability. Therefore, the GO-ASEA method is a new optional tool for the rapid detection of pathogenic microorganisms, which is ideal for food safety monitoring and high-throughput detection.

A Review of the Nucleic Acid-Based Lateral Flow Assay for Detection of Breast Cancer from Circulating Biomarkers at a Point-of-Care in Low Income Countries

The current levels of breast cancer in African women have contributed to the high mortality rates among them. In South Africa, the incidence of breast cancer is also on the rise due to changes in behavioural and biological risk factors. Such low survival rates can be attributed to the late diagnosis of the disease due to a lack of access and the high costs of the current diagnostic tools. Breast cancer is asymptomatic at early stages, which is the best time to detect it and intervene to prevent high mortality rates. Proper risk assessment, campaigns, and access to adequate healthcare need to be prioritised among patients at an early stage. Early detection of breast cancer can significantly improve the survival rate of breast cancer patients, since therapeutic strategies are more effective at this stage. Early detection of breast cancer can be achieved by developing devices that are simple, sensitive, low-cost, and employed at point-of-care (POC), especially in low-income countries (LICs). Nucleic-acid-based lateral flow assays (NABLFAs) that combine molecular detection with the immunochemical visualisation principles, have recently emerged as tools for disease diagnosis, even for low biomarker concentrations. Detection of circulating genetic biomarkers in non-invasively collected biological fluids with NABLFAs presents an appealing and suitable method for POC testing in resource-limited regions and/or LICs. Diagnosis of breast cancer at an early stage will improve the survival rates of the patients. This review covers the analysis of the current state of NABLFA technologies used in developing countries to reduce the scourge of breast cancer.

Sensitive Detection of Staphylococcus aureus by a Colorimetric Biosensor Based on Magnetic Separation and Rolling Circle Amplification

Staphylococcus aureus (S. aureus) is a common foodborne pathogen that causes fever, vomiting, and other intestinal symptoms, and seriously affects human health and social safety. As a result, a reliable and sensitive detection technique for S. aureus must be developed. In this work, we proposed a sandwich assay on vancomycin functionalized magnetic beads (Van-MNPs) for S. aureus detection based on the specific binding between IgG and targets. The Van-MNPs were used as a tool for the separation of target bacteria. The biotin-modified IgG mediates binding between DNA nanoflowers (DNFs) and the target bacteria via interacting with streptavidin. The DNFs prepared by rolling circle amplification (RCA) were employed as a nano-container to enhance the capacity of biotins, and the streptavidin-horseradish peroxidase (SA-HRP) was loaded onto DNFs to catalyze the color change of TMB. Therefore, a colorimetric biosensor based on magnetic separation and rolling circle amplification was developed. The proposed methods for S. aureus detection showed a limit of detection (LOD) of 3.3 × 10³ CFU/mL and excellent specificity. The biosensor has a certain reference value for the detection of S. aureus in juice.

Accurate, rapid and highly sensitive detection of African swine fever virus via graphene oxide-based accelerated strand exchange amplification

African swine fever is an acute, severe and highly contagious infectious disease caused by African swine fever virus (ASFV), posing a huge threat to the global swine industry. Rapid and accurate diagnostic methods are of great significance for the effective prevention and control of ASFV transmission. In this work, we established and evaluated a graphene oxide-based accelerated strand exchange amplification (GO-ASEA) method for rapid, highly sensitive, and quantitative detection of ASFV. The use of GO provided a novel solution reference for improving the specificity of strand exchange amplification and solving the potential false positive problem caused by primer dimers. The detection limit of the GO-ASEA assay was 5.8 × 10^-1 copies per μL of ASFV (equal to 2.9 copies per reaction) or 5.8 × 10⁰ copies per μL of ASFV in spiked swine nasal swabs. The selectivity of the GO-ASEA assay was supported by the ASFV DNA reference material and another seven porcine-derived viruses with similar clinical symptoms. The GO-ASEA assay took only about 29 minutes and was validated with 6 inactivated specimens and 52 swine nasal swabs, showing excellent clinical applicability. The novel assay is an accurate and practical method for rapid, highly sensitive detection of ASFV, and can potentially serve as a robust tool in epidemic prevention and point-of-care diagnosis.

A Novel Class IIb Bacteriocin-Plantaricin EmF Effectively Inhibits Listeria monocytogenes and Extends the Shelf Life of Beef in Combination with Chitosan

Plantaricin EmF separated and identified from L. plantarum 163 was a novel class IIb bacteriocin. The molecular masses of plantaricin Em and F were 1638 and 3702 Da, respectively, with amino acid sequences FNRGGYNFGKSVRH and VFHAYSARGVRNNYKSAVGPADWVISAVRGFIHG, respectively. Plantaricin EmF not only exhibited broad-pH adaptability and thermostability but also showed high efficiency and broad-spectrum antibacterial activity. Its mode of action on L. monocytogenes damaged cell membrane integrity, resulting in the leakage of cytoplasm, changes in cell structure and morphology, and ultimately cell death. Additionally, plantaricin EmF inactivated L. monocytogenes in beef, effectively improving the quality indices of beef, thereby extending its shelf life, especially in combination with chitosan. Plantaricin EmF + 1.0% chitosan extended the shelf life of beef to 15 d, demonstrating its potential application value to replace chemical preservatives to control food-borne pathogenic microorganisms and extend the shelf life of meat and meat products in agriculture and the food industry.

Tri-primer-enhanced strand exchange amplification combined with rapid lateral flow fluorescence immunoassay to detect SARS-CoV-2

The novel coronavirus disease 2019 caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been surging rapidly around the world, which has exposed humanity to unprecedented economic, social and health impacts. To achieve efficient and accurate detection of SARS-CoV-2 on site, we developed and verified a rapid and sensitive fluorescence lateral flow immunoassay based on the innovative enhanced strand exchange amplification (ESEA-LFIA) in this study. With good amplification efficiency for short-sequence targets, ESEA is an ideal choice for the point-of-care testing of SARS-CoV-2 with a high mutation rate. ESEA reaction can be completed in one step and verified by restriction enzyme digestion. The design consisting of three working primers greatly improved the amplification efficiency. Amplification of the target sequences of the RdRP and N genes can be accomplished under the same reaction conditions, and does not require expensive instruments. The sensitivity of the ESEA-LFIA assay targeting the RdRP and N genes was 90 copies per μL and 70 copies per μL, respectively. Specificity tests showed that the novel assay can specifically detect SARS-CoV-2, and had no cross-reactivity with 9 closely-related human pathogenic coronaviruses and other common respiratory pathogens with similar clinical manifestations. The cutoff values of the RdRP and N gene assays are 11 and 12, respectively, and the assays can be completed within 1 h. The novel strategy proposed in this study is a sensitive and specific method for the rapid detection of SARS-CoV-2, and is suitable as an effective potential bioanalytical tool to respond to future regional or global outbreaks of emerging infectious pathogens with high mutation rates.

Accelerated denaturation bubble-mediated strand exchange amplification for rapid and accurate detection of canine parvovirus

Canine parvovirus (CPV), a strong infectious canine pathogen, has been recognized as a threat to canine health worldwide since the 1970s. Although convenient detection methods have been developed, such as the colloidal gold test strip, most of these methods are based on antibody detection, which is relatively ineffective for detecting pathogens during the incubation period. For institutions and businesses with many dogs, e.g., dog training centers and kennels, more sensitive detection methods are required to prevent the swift spread of CPV. Thus, we developed accelerated denaturation bubble-mediated strand exchange amplification (ASEA) for CPV detection, and it is a rapid, convenient, and cost-effective method. ASEA was able to distinguish CPV genomic DNA in a mixture that included canine genomic DNA as well as nucleic acids sourced from nine other common pathogens, with detection of target DNA as low as 8.0 × 10^-18 M within 16.6 min. Coupled with the thermal lysis method modified by us that only requires 3 min to perform, the entire detection procedure can be completed within approximately 20 min and only requires a simple heating block and an ordinary fluorescence PCR instrument. Moreover, ASEA exhibited greater sensitivity than colloidal gold test strips in actual specimen detection. This technique is rapid, easy to perform, and highly sensitive, and therefore, this approach has the potential to rapidly detect CPV in institutions with large populations of dogs.

Rapid point-of-care testing methods/devices for meat species identification: A review

The authentication of animal species is an important issue due to an increasing trend of adulteration and mislabeling of animal species in processed meat products. Polymerase chain reaction is the most sensitive and specific technique for nucleic acid-based animal species detection. However, it is a time-consuming technique that requires costly thermocyclers and sophisticated labs. In recent times, there is a need of on-site detection by point-of-care (POC) testing methods and devices under low-resource settings. These POC devices must be affordable, sensitive, specific, user-friendly, rapid and robust, equipment free, and delivered to the end users. POC devices should also confirm the concept of micro total analysis system. This review discusses POC testing methods and devices that have been developed for meat species identification. Recent developments in lateral flow assay-based devices for the identification of animal species in meat products are also reviewed. Advancements in increasing the efficiency of lateral flow detection are also discussed.

Accurate, rapid and low-cost diagnosis of Mycoplasma pneumoniae via fast narrow-thermal-cycling denaturation bubble-mediated strand exchange amplification

Mycoplasma pneumoniae is a strong infectious pathogen that may cause severe respiratory infections. Since this pathogen may possess a latent period after infection, which sometimes leads to misdiagnosis by traditional diagnosis methods, the establishment of a rapid and sensitive diagnostic method is crucial for transmission prevention and timely treatment. Herein, a novel detection method was established for M. pneumoniae detection. The method, which improves upon a denaturation bubble-mediated strand exchange amplification (SEA) that we developed in 2016, is called accelerated SEA (ASEA). The established ASEA achieved detection of 1% M. pneumoniae genomic DNA in a DNA mixture from multiple pathogens, and the limit of detection (LOD) of ASEA was as low as 1.0 × 10^-17 M (approximately 6.0 × 10³ copies/mL). Considering that the threshold of an asymptomatic carriage is normally recommended as 1.0 × 10⁴ copies/mL, this method was able to satisfy the requirement for practical diagnosis of M. pneumoniae. Moreover, the detection process was finished within 20.4 min, significantly shorter than real-time PCR and SEA. Furthermore, ASEA exhibited excellent performance in clinical specimen analysis, with sensitivity and specificity of 96.2% and 100%, respectively, compared with the "gold standard" real-time PCR. More importantly, similar to real-time PCR, ASEA requires only one pair of primers and ordinary commercial polymerase, and can be carried out using a conventional fluorescence real-time PCR instrument, which makes this method low-cost and easy to accomplish. Therefore, ASEA has the potential for wide use in the rapid detection of M. pneumoniae or other pathogens in large numbers of specimens. Graphical abstract.

Detection of canine parvovirus and feline panleukopenia virus in fecal samples by strand exchange amplification

Canine parvovirus 2 (CPV-2) and feline panleukopenia virus (FPLV) often cause acute enteric disease in their hosts. A simple, rapid, and effective method for the on-site detection of these viruses would be useful. We used a denaturation bubble-mediated strand exchange amplification (SEA) method to successfully detect CPV-2 and FPLV in fecal samples. SEA could detect as little as 3.6 pg/μL of CPV-2 and 6.6 pg/μL of FPLV genomic DNA following a 40-min incubation at an isothermal temperature of 61°C. Unlike PCR, SEA does not require complicated equipment, and positive samples produce a color change that can be visualized by the naked eye. Additionally, SEA is simpler than PCR because no extraction is needed, and heating of the fecal sample at 98°C can be performed with a heating block or water bath. This rapid and effective nucleic acid detection platform could be used as a point-of-care test for the detection of CPV-2 and FPLV.

Recent methods and biosensors for foodborne pathogen detection in fish: progress and future prospects to sustainable aquaculture systems

The aquaculture industry has advanced toward sustainable recirculating systems, in where parameters of food quality are strictly monitored. Despite that, as in the case of conventional aquaculture practices, the recirculating systems also suffer threats from Aeromonas spp., Vibrio spp., Streptococcus spp., among other foodborne pathogens infecting farmed fish. The aquaculture pathogens are routinely detected by conventional PCR methods or antibody-based tests, with the detection protocols confined to laboratory use. Emerging assay technologies and biosensors recently reported in the literature open new opportunities to the development of sensitive, specific, and portable analytical devices to use in the field. Techniques of DNA/RNA analysis, immunoassays and other nanomolecular technologies have been facing important advances in response time, sensitivity, and enhanced power of discrimination among and within species. Moreover, the recent developments of electrochemical and optical signal transduction have facilitated the incorporation of the innovative assays to practical miniaturized devices. In this work, it is provided a critical review over foodborne pathogen detection by existing and promising methods and biosensors applied to fish samples and extended to other food matrices. While isothermal DNA/RNA amplification methods can be highlighted among the assay methods for their promising analytical performance and suitability for point-of-care testing, the electrochemical transduction provides a way to achieve cost-effective biosensors amenable to use in the aquaculture field. The adoption of new methods and biosensors would constitute a step forward in securing sustainable aquaculture systems.

A fully integrated hand-powered centrifugal microfluidic platform for ultra-simple and non-instrumental nucleic acid detection

Hand-powered centrifugal microfluidics combined with isothermal nucleic acid amplification testing (NAAT) have been one of the most promising rapid detection platforms in resource-limited settings. However, current hand-powered centrifuges still suffer from customized instrument-based operation and low rotation rate; and most isothermal NAAT were conducted with complicated reaction systems for DNA detection and required an additional step for RNA detection. Herein, we built a fully hand-powered centrifugal miniaturized NAAT platform inspired by buzzer toys, which embedded sample preparation, strand exchange amplification (SEA) and visual fluorescence detection together. The centrifugal disc was easily fabricated, and operated the mixing in 1 min by simply dragging the looped rope through it with a mean input force of 16.5 N, enabling its rotation rate reach 5000 rpm. In addition, SEA was an ultra-simple one-step DNA or RNA detection method initiated by Bst DNA polymerase and a pair of primers, and thus we took all its merits and integrate it into microfluidic systems firstly. Furthermore, taking Vibrio parahemolyticus as an example, the microfluidic platform achieved DNA or RNA detection within 1 h; and the detection limit of the microchip for artificially spiked oysters was 10³ CFU/g without cumbersome sample preparation, and reached to 10⁰ CFU/g after enrichment. Therefore, we provided an ultra-simple and non-instrumental microfluidic platform powered merely by hands, performing general potential in sample-to-answer NAAT for versatile pathogens in remote regions.

Lateral flow fluorescent immunoassay based on isothermal amplification for rapid quantitative detection of Salmonella spp

Salmonella spp. are zoonotic pathogens of substantial public health concern. To enable detection in the field or under instrument-free conditions, we developed a rapid and robust lateral flow fluorescent immunoassay based on strand exchange amplification (SEA-LFIA) for the quantitative detection of Salmonella spp. As far as we know, this work is the first report regarding the use of Bst DNA polymerase-assisted SEA for fluorescence sensing to detect Salmonella spp. The SEA method was further confirmed by enzymatic digestion and Sanger dideoxy sequencing. The specificity of SEA-LFIA assay was verified by 89 Salmonella strains (18 Salmonella reference strains and 71 clinical isolates) and 15 non-Salmonella reference strains (different genera). The sensitivity of SEA-LFIA assay was 6 × 10⁰ CFU mL^-1 of Salmonella pure culture or 3 × 10⁴ CFU 25 g^-1 of artificially spiked raw chicken meat. Using this assay, it was found that 37 (16%) of the 236 samples collected were positive, which was consistent with the results of conventional PCR. The cutoff value is 15 and SEA-LFIA assay only takes ∼30 min without high equipment and reagent cost. In addition, the proposed strategy can be easily extended by redesigning the corresponding amplification primers to detect target analytes. In conclusion, the optimized SEA-LFIA assay is an efficient and specific method for the detection of Salmonella spp., and can potentially serve as a new on-site diagnostic tool in life sciences.

Primer design strategy for denaturation bubble-mediated strand exchange amplification

Denaturation bubble-mediated strand exchange amplification (SEA) is a novel, rapid isothermal nucleic acid amplification has been applied for point-of-care molecular diagnostic in food safety, meat adulteration, forest disease and animal disease. Nevertheless, the absence of specialized strategy for SEA primers design led to long-time of primer screening progress before SEA reaction execution, which would largely increase the time consuming when SEA is utilized for detecting other new targets. In this present work, we investigated the impact of the following primers' attributes on SEA efficiency, including Tm value, 3' end G/C content, self-complementary and 3' complementary, according to which we demonstrated that optimal Tm value and reaction temperature were all 61 °C, while 3'-terminal nucleotide should be G/C, as the SEA reaction induced by the primers possessing these attributes exhibited significantly lower threshold time (Tt) value. Moreover, self-complementary and 3' complementary of primers should be avoided. Besides, we also discussed the consideration priority order of these factors, which was self-complementary and 3' complementary, Tm value and 3' end G/C content in turn. Because the SEA primer design strategy is first presented, our work will greatly promote the application of SEA in point-of-care test.

Rapid and Simple Detection of Viable Foodborne Pathogen Staphylococcus aureus

Staphylococcus aureus (S. aureus) contamination in food safety has become a worldwide health problem. In this work, we utilized RNA one-step detection of denaturation bubble-mediated Strand Exchange Amplification (SEA) method to realize the detection of viable foodborne pathogen S. aureus. A pair of S. aureus specific primers were designed for the SEA reaction by targeting hypervariable V2 region of 16S rDNA and the amplification reaction was finished about 1 h. The results of amplification reaction could be observed by the naked eyes with a significant color change from light yellow to red to realize the colorimetric detection of S. aureus. Therefore, there only required an isothermal water bath, which was very popular for areas with limited resources. In real sample testing, although the SEA detection was so time-saving compared with the traditional plating method, the SEA method showed great consistency with the traditional plating method. In view of the above-described advantages, we provided a simple, rapid and equipment-free detection method, which had a great potential on ponit-of-care testing (POCT) application. Our method reported here will also provide a POCT detection platform for other food-borne pathogens in food, even pathogenic bacteria from other fields.

Rapid diagnosis of Mycoplasma pneumonia infection by denaturation bubble-mediated strand exchange amplification: comparison with LAMP and real-time PCR

M. pneumoniae infection is often ignored due to its similar clinical symptom with respiratory tract infections caused by bacteria or viruses, and thus leading to misdiagnosis and delayed treatment. It is critical to develop a rapid, sensitive and specific diagnosis method. Denaturation Bubble-mediated Strand Exchange Amplification (SEA) was established, which is an isothermal method with only a primer pair and one Bst DNA polymerase. Notably, colorimetric SEA assay was developed with simple visual readout, making instrument-independent in detection step. The method could detect as low as 1.0 × 10⁴ copies/mL genomic DNA within 60 min. Considering that more than 80% infected patients have 1.0 × 10⁵−1.0 × 10⁷ copies/mL M. pneumonia DNA, SEA is available for the practical diagnosis of M. pneumoniae in clinical specimens. Through comparing 224 sputum specimens, excellent performance of SEA assay with 90.48% sensitivity and 100% specificity relative to real-time PCR was observed. Compared with LAMP, a comparable sensitivity and low false positive rate was observed for SEA method. Therefore, SEA is a promising method for detecting M. pneumoniae directly from clinical specimens, which is especially suitable for point-of-care testing in primary care facilities and resource-limited settings with minimal equipment and technological expertises.

Rapid Detection of the Bursaphelenchus Xylophilus by Denaturation Bubble-mediated Strand Exchange Amplification

Bursaphelenchus xylophilus (B. xylophilus) is one of the most important causal agents of infectious diseases in forest pathology. Obviously, the rapid detection of B. xylophilus is an urgent need for its prevention and cure. We have developed a detection method of B. xylophilus by strand exchange amplification (SEA). This method could detect 10⁵ copies of genomic DNA of B. xylophilus, and it was sufficiently sensitive to detect a single nematode as short as 40 min. Moreover, because the amplification result could be visualized by the naked eyes, the only equipment required throughout the process was a simple isothermal block. Therefore, our method would be a potential for developing on-site detection of B. xylophilus to prevent and control its spread.

A Simple Mannose-Coated Poly (p-Phenylene Ethynylene) for Qualitative Bacterial Capturing

A mannose-functionalized poly (p-phenylene ethynylene) was rationally designed to achieve selective detection of bacteria. The polymer was constructed as a signaling unit and was modified by attaching aminoethyl mannose using the carboxylic acid group at the end of the linker. Incubation of Escherichia coli with the polymer yielded fluorescent bacteria aggregates through polyvalent interactions. The utility of the mannose functionalized polymer to detect E. coli expressing functional FimH mannose-specific lectin on their surface was also demonstrated. The sugar units displayed on the surface of the polymer retained their functional ability to interact with mannose-binding lectin. To determine the optimum binding time, we measured the fluorescence intensity of the polymer-bacteria suspension at intervals. Our results showed that binding in this system will reach an optimum level within 30 min of incubation. The polymer’s affinity for bacteria has been demonstrated and bacteria with a concentration of 10³ CFU mL⁻¹ can be detected by this system.

Rapid Colorimetric Assay for Detection of Listeria monocytogenes in Food Samples Using LAMP Formation of DNA Concatemers and Gold Nanoparticle-DNA Probe Complex

Listeria monocytogenes is a major foodborne pathogen of global health concern. Herein, the rapid diagnosis of L. monocytogenes has been achieved using loop-mediated isothermal amplification (LAMP) based on the phosphatidylcholine-phospholipase C gene (plcB). Colorimetric detection was then performed through the formation of DNA concatemers and a gold nanoparticle/DNA probe complex (GNP/DNA probe). The overall detection process was accomplished within approximately 1 h with no need for complicated equipment. The limits of detection for L. monocytogenes in the forms of purified genomic DNA and pure culture were 800 fg and 2.82 CFU mL⁻¹, respectively. No cross reactions were observed from closely related bacteria species. The LAMP-GNP/DNA probe assay was applied to the detection of 200 raw chicken meat samples and compared to routine standard methods. The data revealed that the specificity, sensitivity, and accuracy were 100, 90.20, and 97.50%, respectively. The present assay was 100% in conformity with LAMP-agarose gel electrophoresis assay. Five samples that were negative by both assays appeared to have the pathogen at below the level of detection. The assay can be applied as a rapid direct screening method for L. monocytogenes.