Evaluation of a loop-mediated isothermal amplification (LAMP) method for rapid on-site detection of horse meat

Recent advancements with loop-mediated isothermal amplification (LAMP) in assessment of the species authenticity with meat and seafood products

Species adulteration or mislabeling with meat and seafood products could negatively affect the fair trade, wildlife conservation, food safety, religion aspect, and even the public health. While PCR-based methods remain the gold standard for assessment of the species authenticity, there is an urgent need for alternative testing platforms that are rapid, accurate, simple, and portable. Owing to its ease of use, low cost, and rapidity, LAMP is becoming increasingly used method in food analysis for detecting species adulteration or mislabeling. In this review, we outline how the features of LAMP have been leveraged for species authentication test with meat and seafood products. Meanwhile, as the trend of LAMP detection is simple, rapid and instrument-free, it is of great necessity to carry out end-point visual detection, and the principles of various end-point colorimetry methods are also reviewed. Moreover, with the aim to enhance the LAMP reaction, different strategies are summarized to either suppress the nonspecific amplification, or to avoid the results of nonspecific amplification. Finally, microfluidic chip is a promising point-of-care method, which has been the subject of a great deal of research directed toward the development of microfluidic platforms-based LAMP systems for the species authenticity with meat and seafood products.

Rapid Detection of Hepatitis A Virus in Foods Using a Bioluminescent Assay in Real-Time (BART) and Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) Technology

Foodborne hepatitis A infections have been considered as a major threat for public health worldwide. Increased incidences of hepatitis A virus (HAV) infection has been associated with growing global trade of food products. Rapid and sensitive detection of HAV in foods is very essential for investigating the outbreaks. Real-time RT-PCR has been most widely used for the detection of HAV by far. However, the technology relies on fluorescence determination of the amplicon and requires sophisticated, high-cost instruments and trained personnel, limiting its use in low resource settings. In this study, a robust, affordable, and simple assay, reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay in combination with a bioluminescence-based determination of amplification in real-time (BART), was developed for the detection of HAV in different food matrices, including green onion, strawberry, mussel, and milk. The efficiencies of a one-step RT-LAMP-BART and a two-step RT-LAMP-BART were investigated for the detection of HAV in different food matrices and was compared with that of real-time RT-PCR. The sensitivity of the RT-LAMP-BART assay was significantly affected by Mg²⁺ concentration (P < 0.05), in addition to primer quality. The optimal Mg²⁺ concentration was 2 mM for one-step RT-LAMP-BART and 4 mM for two-step RT-LAMP-BART. Compared with cartridge-purified primers, HPLC-purified primers could greatly improve the sensitivity of the RT-LAMP-BART assay (P < 0.05). For detecting HAV in different food matrices, the performance of two-step RT-LAMP-BART was comparable with that of real-time RT-PCR and was better than that of one-step RT-LAMP-BART. The detection limit of the two-step RT-LAMP-BART for HAV in green onion, strawberry, mussel, and milk was 8.3 × 10⁰ PFU/15 g, 8.3 × 10¹ PFU/50 g, 8.3 × 10⁰ PFU/5 g, and 8.3 × 10⁰ PFU/40 mL, respectively. The developed RT-LAMP-BART was an effective, simple, sensitive, and robust method for foodborne HAV detection.

Development of novel isothermal-based DNA amplification assay for detection of pig tissues in adulterated meat

For the first time, we describe an innovative polymerase spiral reaction (PSR) assay for the rapid, simple, and accurate detection of pig tissues or pork in adulterated meat including heat-treated and processed ones. The PSR assay specifically targeting the mitochondrial cytochrome b (cyt-b) gene of the pig was successfully optimized permitting assay results in 65 min time. The developed detection method was 100% specific amplifying only the cyt-b gene and displaying negative results with all the tested non-pork meats. The sensitivity of the developed PSR (760 fg porcine DNA) was tenfold better than the end-point PCR and able to detect heat-treated (121 °C) and adulterated (0.5% pork in beef) meat and processed pork products such as sausages, salami, meatball, soup, curry, etc. The developed PSR-based method can be used for point-of-care detection with minimum instrumentation and technical expertise to guarantee instant clearance of exported and imported meat products. This is the first time that PSR has been adapted for food authenticity purposes.

Sensitive colorimetric detection of antibiotic resistant Staphylococcus aureus on dairy farms using LAMP with pH-responsive polydiacetylene

Rapidly and accurately detecting antibiotic-resistant pathogens in agriculture and husbandry is important since these represent a major threat to public health. While much attention has been dedicated to detecting now-common resistant bacteria, such as methicillin-resistant Staphylococcus aureus, fewer methods have been developed to assess resistance against macrolides in Staphylococcus aureus (SA). Here, we report a visual on-site detection system for macrolide resistant SA in dairy products. First, metagenomic sequencing in raw milk, cow manure, water and aerosol deposit collected from dairy farms around Tianjin was used to identify the most abundant macrolide resistance gene, which was found to be the macB gene. In parallel, SA housekeeping genes were screened to allow selective identification of SA, which resulted in the selection of the SAOUHSC_01275 gene. Next, LAMP assays targeting the above-mentioned genes were developed and interpreted by agarose gel electrophoresis. For on-site application, different pH-sensitive colorimetric LAMP indicators were compared, which resulted in selection of polydiacetylene (PDA) as the most sensitive candidate. Additionally, a semi-quantitative detection could be realized by analyzing the RGB information via smartphone with a LOD of 1.344 × 10-7 ng/μL of genomic DNA from a milk sample. Finally, the proposed method was successfully carried out at a real farm within 1 h from sample to result by using freeze-dried reagents and portable devices. This is the first instance in which PDA is used to detect LAMP products, and this generic read-out system can be expanded to other antibiotic resistant genes and bacteria.

On-site environmental DNA detection of species using ultrarapid mobile PCR

Molecular methods, including those for environmental DNA (eDNA), provide essential information for biological and conservation sciences. Molecular measurements are often performed in the laboratory, which limits their scope, especially for rapid on-site analysis. eDNA methods for species detection provide essential information for the management and conservation of species and communities in various environments. We have developed an innovative novel method for on-site eDNA measurements using an ultrarapid mobile PCR platform. We tested the ability of our method to detect the distribution of silver carp, Hypophthalmichthys molitrix, in rivers and lakes. Our method reduced the measurement time to 30 min and provided high detectability of aquatic organisms compared to national observation surveys that use multiple fishing nets and laboratory extraction/detection using a benchtop qPCR platform. Our on-site eDNA method can be immediately applied to various taxa and environments.

Loop-mediated isothermal amplification technique: principle, development and wide application in food safety

Food safety is a major and enduring challenge and has a profound impact on the quality of human life. Loop-mediated isothermal amplification (LAMP) is a relatively novel gene amplification method under isothermal conditions with rapidity, simplicity and high specificity. This review will describe the principles and development of the LAMP technique along with its advantages and disadvantages, such as LAMP integrated on classical microfluidic chips, paper-chips, electrochemical devices, nanomaterials and digital devices. Moreover, we will systematically and comprehensively review its applications in the field of food safety, such as in the detection of foodborne pathogens, allergens and organophosphorus pesticides and genetically modified organisms; finally its development trends in food safety will be discussed.

Rainbow trout (Oncorhynchus mykiss) identification in processed fish products using loop-mediated isothermal amplification and polymerase chain reaction assays

BACKGROUND

Financial loss and health risk caused by the substitution of rainbow trout for other salmonid species have become a common issue around the world. The situation could be further exacerbated in China by the 'abused' common name of San Wen Yu (the corresponding Chinese ideogram ) for salmonids, considering the absence of a standardized naming system for seafood species. To prevent such episodes, the present study aimed to develop novel loop-mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR) assays targeting the mitochondrial cytochrome b gene for rapid identification of rainbow trout in processed fish products.

RESULTS

Rainbow trout-specific primers (LAMP and PCR) were designed, and the specificity against 23 different fish species was confirmed. The minimum amount of detectable DNA for LAMP assay reached 500 pg, up to 10-fold less than for PCR assay. In addition to agarose gel electrophoresis, naked-eye inspection of the LAMP-positive samples using SYBR Green I under daylight or ultraviolet light was also validated. Finally, commercial San Wen Yu products made from rainbow trout could be accurately identified using the newly developed LAMP and PCR assays, further cross-confirmed by mini DNA barcoding and neighbor-joining dendrograms.

CONCLUSIONS

The LAMP and PCR assays established in the study allow a fast and accurate identification of rainbow trout in processed fish products. © 2020 Society of Chemical Industry.

Detection of porcine-derived ingredients from adulterated meat based on real-time loop-mediated isothermal amplification

Increasingly globalized and complex food supply chains contribute to a growing problem of meat fraud. Meat adulteration with pork is especially exceptionable to the global population for health concern and religious faith reasons. To prevent unfair competition and protect consumer rights, an efficient and rapid assay to identify the species of meat products is crucial. In this study, a real-time loop-mediated isothermal amplification (real-time LAMP) assay was developed for the detection of a porcine gene in meat products. The designed primers were highly selective for the porcine gene. The amplification showed no cross-reactivity with 11 other meats. The established method required 20 min with an initial amplification curve of approximately 10 min and demonstrated a detection limit of 1.76 pg/μL porcine DNA, which is 1000 times more sensitive than PCR. This study is the first attempt at detecting porcine-derived ingredients using a real-time LAMP assay in commercial products. This method meets specificity, rapidness, robustness, and sensitivity criteria; its practical application will greatly aid in battling adulteration in the food industry.