Systematic loop-mediated isothermal amplification assays for rapid detection and characterization of Salmonella spp., Enteritidis and Typhimurium in food samples

Application of MinION Long-Read Sequencer for Semi-targeted Detection of Foodborne Pathogens

Foodborne pathogens remain a serious health issue in developed and developing countries. Safeness of food products has been assured for years with culture-based microbiological methods; however, these present several limitations such as turnaround time and extensive hands-on work, which have been typically address taking advantage of DNA-based methods such as real-time PCR (qPCR). These, and other similar techniques, are targeted assays, meaning that they are directed for the specific detection of one specific microbe. Even though reliable, this approach suffers from an important limitation that unless specific assays are design for every single pathogen potentially present, foods may be considered erroneously safe. To address this problem, next-generation sequencing (NGS) can be used as this is a nontargeted method; thus it has the capacity to detect every potential threat present. In this chapter, a protocol for the simultaneous detection and preliminary serotyping of Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, and Escherichia coli O157:H7 is described.

Research progress of loop-mediated isothermal amplification in the detection of Salmonella for food safety applications

Salmonella, the prevailing zoonotic pathogen within the Enterobacteriaceae family, holds the foremost position in global bacterial poisoning incidents, thereby signifying its paramount importance in public health. Consequently, the imperative for expeditious and uncomplicated detection techniques for Salmonella in food is underscored. After more than two decades of development, loop-mediated isothermal amplification (LAMP) has emerged as a potent adjunct to the polymerase chain reaction, demonstrating significant advantages in the realm of isothermal amplification. Its growing prominence is evident in the increasing number of reports on its application in the rapid detection of Salmonella. This paper provides a systematic exposition of the technical principles and characteristics of LAMP, along with an overview of the research progress made in the rapid detection of Salmonella using LAMP and its derivatives. Additionally, the target genes reported in various levels, including Salmonella genus, species, serogroup, and serotype, are summarized, aiming to offer a valuable reference for the advancement of LAMP application in Salmonella detection. Finally, we look forward to the development direction of LAMP and expect more competitive methods to provide strong support for food safety applications.

Rapid and sensitive detection of Salmonella in agro-Food and environmental samples: A review of advances in rapid tests and biosensors

Salmonella is as an intracellular bacterium, causing many human fatalities when the host-specific serotypes reach the host gastrointestinal tract. Nontyphoidal Salmonella are responsible for numerous foodborne outbreaks and product recalls worldwide whereas typhoidal Salmonella are responsible for Typhoid fever cases in developing countries. Yet, Salmonella-related foodborne disease outbreaks through its food and water contaminations have urged the advancement of rapid and sensitive Salmonella-detecting methods for public health protection. While conventional detection methods are time-consuming and ineffective for monitoring foodstuffs with short shelf lives, advances in microbiology, molecular biology and biosensor methods have hastened the detection. Here, the review discusses Salmonella pathogenic mechanisms and its detection technology advancements (fundamental concepts, features, implementations, efficiency, benefits, limitations and prospects). The time-efficiency of each rapid test method is discussed in relation to their limit of detections (LODs) and time required from sample enrichment to final data analysis. Importantly, the matrix effects (LODs and sample enrichments) were compared within the methods to potentially speculate Salmonella detection from environmental, clinical or food matrices using certain techniques. Although biotechnological advancements have led to various time-efficient Salmonella-detecting techniques, one should consider the usage of sophisticated equipment to run the analysis by moderately to highly trained personnel. Ultimately, a fast, accurate Salmonella screening that is readily executed by untrained personnels from various matrices, is desired for public health procurement.

Evaluation of the Novel mTA10 Selective Broth, MSB, for the Co-Enrichment and Detection of Salmonella spp., Escherichia coli O157 and Listeria monocytogenes in Ready-to-Eat Salad Samples

Multiplex assays implementing DNA-based methods have been demonstrated as suitable alternatives to culture-based microbiological methods; however, in most cases, they still require a suitable enrichment step. Finding suitable enrichment conditions for different bacteria may result in challenges. In the present study, a novel selective broth named MSB (mTA10 selective broth) was formulated for the simultaneous recovery of Salmonella spp., E. coli O157:H7 and L. monocytogenes. Attention was paid to ensure the optimal enrichment of L. monocytogenes as its enrichment is more challenging. To this end, cellobiose was added to increase the growth of L. monocytogenes, and sodium pyruvate was also added to improve the recovery of stressed bacteria. Four selective agents were added, namely nalidixic acid, sodium cholate, lithium chloride and potassium tellurite, to control the growth of interfering microorganisms. It was concluded that the novel broth was suitable for the simultaneous enrichment of the target pathogens, allowing them to reach concentrations higher than 7 log CFU/mL for each bacterium in pure culture. Furthermore, all heavily contaminated ready-to-eat salad samples reached concentrations higher than 5 log CFU/g. Finally, after 24 h of enrichment of spiked salad, it was possible to detect concentrations below 10 CFU/25 g.

Phage amplification coupled with loop-mediated isothermal amplification (PA-LAMP) for same-day detection of viable Salmonella Enteritidis in raw poultry meat

Salmonella Enteritidis is the main serotype responsible for human salmonellosis in the European Union. One of the main sources of Salmonella spp. in the food chain are poultry products, such as eggs or chicken meat. In recent years, molecular methods have become an alternative to culture dependent methods for the rapid screening of Salmonella spp. In this work, the strain S. Enteritidis S1400, and previously isolated and characterized bacteriophage PVP-SE2, were used to develop and evaluate a same-day detection method combining Phage Amplification and Loop-mediated isothermal amplification (PA-LAMP) to specifically detect viable S. Enteritidis in chicken breast. This method is based on the detection of the phage DNA rather than bacterial DNA. The virus is added to the sample during pre-enrichment in buffered peptone water, where it replicates in the presence of viable S. Enteritidis. The detection of phage DNA allows, on the one hand to detect viable bacteria, since viruses only replicate in them, and on the other hand to increase the sensitivity of the method since for each infected S. Enteritidis cell, hundreds of new viruses are produced. Two different PA-LAMP detection strategies were evaluated, a real time fluorescence and a naked-eye detection. The present method could down to 0.2 fg/μL of pure phage DNA and a concentration of viral particles of 2.2 log PFU/mL. After a short Salmonella recovery step of 3 h and a co-culture of 4 h of the samples with phage particles, both real-time fluorescence and naked-eye method showed a LoD95 of 6.6 CFU/25 g and a LoD50 of 1.5/25 g in spiked chicken breast samples. The entire detection process, including DNA extraction and LAMP analysis, can be completed in around 8 h. In the current proof-of-concept, the novel PA-LAMP obtained comparable results to those of the reference method ISO 6579, to detect Salmonella Enteritidis in poultry meat.

Current and Future Advances in the Detection and Surveillance of Biosecurity-Relevant Equine Bacterial Diseases Using Loop-Mediated Isothermal Amplification (LAMP)

Horses play an important role throughout the world, whether for work, culture, or leisure, providing an ever-growing significant contribution to the economy. The increase in importation and movement of horses, both nationally and internationally, has inevitably allowed for the global equine industry to grow. Subsequently, however, the potential for transmission of fatal equine bacterial diseases has also escalated, and devasting outbreaks continue to occur. To prevent such events, disease surveillance and diagnosis must be heightened throughout the industry. Current common, or "gold-standard" techniques, have shown to be inadequate at times, thus requiring newer technology to impede outbreaks. Loop-mediated isothermal amplification (LAMP) has proven to be a reliable, rapid, and accessible tool in both diagnostics and surveillance. This review will discuss equine bacterial diseases of biosecurity relevance and their current diagnostic approaches, as well as their respective LAMP assay developments. Additionally, we will provide insight regarding newer technology and advancements associated with this technique and their potential use for the outlined diseases.

Label-Free Sequence-Specific Visualization of LAMP Amplified Salmonella via DNA Machine Produces G-Quadruplex DNAzyme

Salmonella is one of four key global causes of diarrhea, and in humans, it is generally contracted through the consumption of contaminated food. It is necessary to develop an accurate, simple, and rapid method to monitor Salmonella in the early phase. Herein, we developed a sequence-specific visualization method based on loop-mediated isothermal amplification (LAMP) for the detection of Salmonella in milk. With restriction endonuclease and nicking endonuclease, amplicons were produced into single-stranded triggers, which further promoted the generation of a G-quadruplex by a DNA machine. The G-quadruplex DNAzyme possesses peroxidase-like activity and catalyzes the color development of 2,2'-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) as the readouts. The feasibility for real samples analysis was also confirmed with Salmonella spiked milk, and the sensitivity was 800 CFU/mL when observed with the naked eye. Using this method, the detection of Salmonella in milk can be completed within 1.5 h. Without the involvement of any sophisticated instrument, this specific colorimetric method can be a useful tool in resource-limited areas.

A rapid and facile analytical approach to detecting Salmonella Enteritidis with aptamer-based surface-enhanced Raman spectroscopy

Salmonella should be absence in pharmaceutical preparations and foods according to regulations in many countries. Up to now, rapidly detecting Salmonella at 1 CFU·[10 g (mL) ]^-1 in pharmaceutical preparation or 1 CFU·[25 g (mL) ]^-1 in food samples is still a challenge. Herein, we present an aptamer-based surface-enhanced Raman spectroscopy (SERS) method for rapidly detecting Salmonella Enteritidis by using a handheld Raman instrument. The aptamer could specifically recognize S. Enteritidis, and 4-MBA self-assembled on the surface of Au@Ag NPs was used as a Raman reporter molecule. The method was validated to be high specific with no interference from other five pathogenic bacteria. It could identify S. Enteritidis contaminant at ∼ 1 CFU·(10 g)^-1 spiked level in a real sample (Wenxin granule, a botanical drug) after 6 h of enrichment. The detection time was much shorter than that of the methods (more than 54 ∼ 96 h) in the standards of pharmaceutical preparations and foods. In addition, the method could quantitatively determinate S. Enteritidis with satisfactory results. The SERS peak intensities of 4-MBA at 1072 cm^-1 showed a good linear correlation (R² = 0.9873) with the logarithms of S. Enteritidis concentrations ranging from 4.17 × 10² to 1.39 × 10⁷ CFU·mL^-1. T-test result (P = 0.425) revealed that there was no significant difference between the determination results obtained by the SERS method and the plate counting method. Therefore, the study indicated that the method was practical and reliable, and it could be a promising alternative for the on-site detection of S. Enteritidis.

Efficacy and Quality Attributes of Antimicrobial Agent Application via a Commercial Electrostatic Spray Cabinet To Inactivate Salmonella on Chicken Thigh Meat

ABSTRACT

Salmonella is a foodborne pathogen associated with poultry meat. This study aimed to determine the efficiency and quality attributes of two antimicrobial agents to reduce Salmonella on raw chicken meat when applied individually and in combination using an electrostatic spray cabinet. Thus, 5 log CFU/g of nonpathogenic, rifampin-resistant Salmonella Typhimurium was inoculated on skinless, boneless, raw chicken thigh meat and passed through an electrostatic spray cabinet while being sprayed with 5% lauric arginate (LAE), and 100, 1,000, 1,500, and 1,750 ppm of peracetic acid (PAA). Spraying of 5% LAE for 45 s significantly reduced Salmonella by 5 log (P < 0.05). The 1,500 ppm of PAA reduced Salmonella significantly within 45 s (1.157 log). Spraying of 1,500 ppm of PAA followed by LAE within 15 s reduced Salmonella significantly more than vice versa (P < 0.05). The color, water holding capacity, and texture did not differ significantly but resulted in significantly strong aroma and flavor. Both LAE and PAA efficiently reduced Salmonella when applied in an electrostatic spray cabinet on raw chicken thigh meat. The results suggest that the sequential order of application of antimicrobial agents is important to improve the safety and quality of raw chicken thigh meat.

HIGHLIGHTS

Rapid detection of trace Salmonella in milk using an effective pretreatment combined with droplet digital polymerase chain reaction

Salmonella is one of the most dangerous food-borne pathogens around the world to cause a threat to humans and it is urgent to develop the rapid detection method of trace Salmonella in food. Although many advanced techniques have been widely applied to shorten the detection time, the pretreatment method usually used of traditional enrichment and plate culturing to separate Salmonella are complicated and time-consuming. Herein, we developed an effective pretreatment method based on in situ enrichment culture with an immunomagnetic separation step, combined with droplet digital polymerase chain reaction (ddPCR) technology to achieve rapid detection of trace Salmonella in milk, which allowed detecting as low as 10^-1 CFU/mL level of Salmonella. It took 8 h to perform the entire testing process from pretreatment to ddPCR detection and analysis. The pretreatment method could be a suitable platform integrating with many detection techniques for the rapid detection of trace Salmonella.

Faster monitoring of the invasive alien species (IAS) Dreissena polymorpha in river basins through isothermal amplification

Zebra mussel (Dreissena polymorpha) is considered as one of the 100 most harmful IAS in the world. Traditional detection methods have limitations, and PCR based environmental DNA detection has provided interesting results for early warning. However, in the last years, the development of isothermal amplification methods has received increasing attention. Among them, loop-mediated isothermal amplification (LAMP) has several advantages, including its higher tolerance to the presence of inhibitors and the possibility of naked-eye detection, which enables and simplifies its potential use in decentralized settings. In the current study, a real-time LAMP (qLAMP) method for the detection of Dreissena polymorpha was developed and tested with samples from the Guadalquivir River basin, together with two real-time PCR (qPCR) methods using different detection chemistries, targeting a specific region of the mitochondrial gene cytochrome C oxidase subunit I. All three developed approaches were evaluated regarding specificity, sensitivity and time required for detection. Regarding sensitivity, both qPCR approaches were more sensitive than qLAMP by one order of magnitude, however the qLAMP method proved to be as specific and much faster being performed in just 9 min versus 23 and 29 min for the qPCR methods based on hydrolysis probe and intercalating dye respectively.

Application of Short Pre-enrichment, and Double Chemistry Real-Time PCR, Combining Fluorescent Probes and an Intercalating Dye, for Same-Day Detection and Confirmation of Salmonella spp. and Escherichia coli O157 in Ground Beef and Chicken Samples

Molecular methods, particularly those based on real-time PCR (qPCR), have become a popular approach to detect pathogens in food samples. This technique may take advantage of hydrolysis fluorescent probes for increased specificity. Even though suitable, this approach loses the capacity of performing result confirmation by melt curve analysis. In the current study, we developed an alternative approach, combining fluorescent probes along with an intercalating dye (SYBR Green) in order to simultaneously detect, and confirm the result, of two foodborne pathogens (Salmonella spp. and Escherichia coli O157). This new approach named double chemistry qPCR was combined with a short pre-enrichment in order to obtain a multiplex “same-day” detection method for the selected pathogens. The evaluation of the novel method in spiked food samples (ground beef and chicken breast) obtained values of relative sensitivity, specificity, and accuracy higher than 95%, and Cohen’s kappa of 0.92, with a Limit of Detection₉₅ below 5 cfu/25 g, demonstrating its reliability. In addition to this, the method was challenged by inoculating heat-stressed bacteria as well as dead ones. It was observed that it was also possible to detect stressed bacteria with an initial inoculation level below 10 cfu/25 g. Also, it was noticed that high initial concentration of either pathogen (higher than 10⁴ cfu/25 g) was needed in order to generate false positive results due to the presence of dead bacteria, thus the method presents potential for its application in the specific detection of live microorganisms.

Green synthesis of lignin nano- and micro-particles: Physicochemical characterization, bioactive properties and cytotoxicity assessment

Lignin particles (LPs) have gained prominence due to their biodegradability and bioactive properties. LP production at nano and micro scale produced from organosolv lignin and the understanding of size's effect on their properties is unexplored. This work aimed to produce and characterize lignin nanoparticles and microparticles using a green synthesis process, based on ethanol-solubilized lignin and water. Spherical shape LPs, with a mean size of 75 nm and 215 nm and with a low polydispersity were produced, as confirmed by transmission electron microscopy and dynamic light scattering. LPs thermal stability improved over raw lignin, and the chemical structure of lignin was not affected by the production method. The antimicrobial tests proved that LPs presented a bacteriostatic effect on Escherichiacoli and Salmonella enterica. Regarding the antioxidant potential, LPs had a good antioxidant activity that increased with the reaction time and LPs concentration. LPs also presented an antioxidant effect against intracellular ROS, reducing the intracellular ROS levels significantly. Furthermore, the LPs showed a low cytotoxic effect in Caco-2 cell line. These results showed that LPs at different scales (nano and micro) present biological properties and are safe to be used in different high value industrial sectors, such as biomedical, pharmaceutical and food.

Direct detection of Salmonella from poultry samples by DNA isothermal amplification

1. Salmonellosis is one of the most important diseases in public health and it is usually associated with poultry product consumption. This study aimed to validate rapid methods to detect Salmonella spp. from poultry samples. 2. A DNA isothermal amplification method, previously developed for other matrices, was applied for the specific detection of Salmonella spp. from various samples, including poultry tissues, drag and boot swabs, faeces and feed. A new procedure was validated with Salmonella spp. serotypes and isolates from other enteric bacterial species, as well as naturally contaminated poultry samples. 3. The study demonstrated the successful development and implementation of a procedure, including a DNA isothermal amplification method, for the detection of Salmonella spp. directly from tissues, drag and boot swabs, faeces and feed. The whole procedure can be performed in less than 24 hours and it has been successfully used in a veterinary diagnostic laboratory.

Application of Recombinase Polymerase Amplification with Lateral Flow for a Naked-Eye Detection of Listeria monocytogenes on Food Processing Surfaces

The continuous contamination of foods with L. monocytogenes, highlights the need for additional controls in the food industry. The verification of food processing plants is key to avoid cross-contaminations, and to assure the safety of the food products. In this study, a new methodology for the detection of L. monocytogenes on food contact surfaces was developed and evaluated. It combines Recombinase Polymerase Amplification (RPA) with the lateral flow (LF) naked-eye detection. Different approaches for the recovery of the bacteria from the surface, the enrichment step and downstream analysis by RPA-LF were tested and optimized. The results were compared with a standard culture-based technique and qPCR analysis. Sampling procedure with sponges was more efficient for the recovery of the bacteria than a regular swab. A 24 h enrichment in ONE broth was needed for the most sensitive detection of the pathogen. By RPA-LF, it was possible to detect 1.1 pg/µL of pure L. monocytogenes DNA, and the complete methodology reached a LoD₅₀ of 4.2 CFU/cm² and LoD₉₅ of 18.2 CFU/cm². These results are comparable with the culture-based methodology and qPCR. The developed approach allows for a next-day detection without complex equipment and a naked-eye visualization of the results.

Multiplex Detection of Salmonella spp., E. coli O157 and L. monocytogenes by qPCR Melt Curve Analysis in Spiked Infant Formula

Food poisoning continue to be a threat in the food industry showing a need to improve the detection of the pathogen responsible for the hospitalization cases and death. DNA-based techniques represent a real advantage and allow the detection of several targets at the same time, reducing cost and time of analysis. The development of new methodology using SYBR Green qPCR for the detection of L. monocytogenes, Salmonella spp. and E. coli O157 simultaneously was developed and a non-competitive internal amplification control (NC-IAC) was implemented to detect reaction inhibition. The formulation and supplementation of the enrichment medium was also optimized to allow the growth of all pathogens. The limit of detection (LoD) 95% obtained was <1 CFU/25 g for E. coli O157, and 2 CFU/25 g for Salmonella spp. and L. monocytogenes and regarding the multiplex detection a LoD 95% of 1.7 CFU/25 g was observed. The specificity, relative sensitivity and accuracy of full methodology were 100% and the use of the NC-IAC allowed the reliability of the results without interfering with the sensitivity of the methodology. The described study proved to obtain results comparable to those of probe-based qPCR, and more economically than classical high resolution melting qPCR, being both important aspects for its implementation in the food industry.

Comparative study of multiplex real-time recombinase polymerase amplification and ISO 11290-1 methods for the detection of Listeria monocytogenes in dairy products

Dairy products have been implicated in foodborne infections caused by different bacterial pathogens. Among them, Listeria monocytogenes is of particular concern due to its ubiquity, resistance to sanitation processes and high mortality rates resulting from infection. These issues make the development of novel methods for the rapid detection of this bacterium of high interest. The evaluation of a novel multiplex real-time Recombinase Polymerase Amplification method including an internal amplification control is reported in the present work. The method performance was compared to that of the European reference method (ISO 11290-1) for the detection of the species in samples from 40 commercial products, including 14 UHT milk samples, 16 hard cheese samples, 6 infant dairy preparation samples and 4 fresh cheese samples. A limit of detection below 10 cfu/25 g or mL sample was achieved, and values higher than 90% were obtained for relative sensitivity, specificity, accuracy, positive and negative predictive values and the index (kappa) of concordance. Analysis was achieved within one working day, compared to the six days required using the ISO method. Moreover, slight modification of the ISO 11290-1 method to include secondary enrichment in half Fraser broth resulted in the confirmation of all positive samples.

Highly Sensitive and Specific Detection and Serotyping of Five Prevalent Salmonella Serovars by Multiple Cross-Displacement Amplification

Salmonella is a common cause of foodborne disease worldwide, including Australia. More than 85% of outbreaks of human salmonellosis in Australia were caused by five Salmonella serovars. Rapid, accurate, and sensitive identification of Salmonella serovars is vital for diagnosis and public health surveillance. Recently, an isothermal amplification technique, termed multiple cross-displacement amplification (MCDA), has been employed to detect Salmonella at the species level. Herein, seven MCDA assays were developed and evaluated for rapid detection and differentiation of the five most common Salmonella serovars in Australia: Typhimurium, Enteritidis, Virchow, Saintpaul, and Infantis. MCDA primer sets were designed by targeting seven serovar/lineage-specific gene markers identified through genomic comparisons. The sensitivity and specificity of the seven MCDA assays were evaluated using 79 target strains and 32 nontarget strains. The assays were all highly sensitive and specific to target serovars, with the sensitivity ranging from 92.9% to 100% and the specificity from 93.3% to 100%. The limit of detection of the seven MCDA assays was 50 fg per reaction (10 copies) from pure DNA, and positive results were detected in as little as 8 minutes. These seven MCDA assays offer a rapid, accurate, and sensitive serotyping method. With further validation in clinically relevant conditions, these assays could be used for culture-independent serotyping of common Salmonella serovars directly from clinical samples.

Evaluation and implementation of commercial antibodies for improved nanoparticle-based immunomagnetic separation and real-time PCR for faster detection of Listeria monocytogenes

L. monocytogenes continues to be a major health issue in Europe, as well as worldwide. Faster methods, not only for detection, but also for sample preparation are of great interest particularly for this slow-growing pathogen. Immunomagnetic separation has been previously reported to be an effective way to concentrate bacteria, and remove inhibitors. In the present study, different commercial antibodies were evaluated to select the most appropriate one, in order to develop a highly specific method. Additionally, magnetic nanoparticles, instead of microparticles, were selected due to their reported advantages (higher surface-volume ration and faster kinetics). Finally, the separation protocol, with a calculated capture efficiency of 95%, was combined with real-time PCR for highly sensitive detection of the concentrated bacteria. The optimized IMS-qPCR allowed to reduce hands-on time in the sample treatment, without affecting the overall performance of the method as a very low limit of detection was still obtained (9.7 CFU/ 25 g) with values for sensitivity, specificity, accuracy, positive and negative predictive values of 100%, resulting in a kappa index of concordance of 1.00. These results were obtained in spiked food samples of different types (chicken, fish, milk, hard and fresh cheese), further demonstrating the applicability of the optimized methodology presented.

Combination of Immunomagnetic Separation and Real-Time Recombinase Polymerase Amplification (IMS-qRPA) for Specific Detection of Listeria monocytogenes in Smoked Salmon Samples

Nowadays, Listeria monocytogenes continues to be a major health issue. Therefore, improvements in the speed and reliability of its detection are still needed. In the present study, the combination of real-time Recombinase Polymerase Amplification (qRPA) with immunomagnetic separation (IMS) is described. The proposed methodology was tested against a real-time PCR method, and was successfully applied to 50 smoked salmon samples spiked at levels ranging from 2 to 9.3 × 10² cfu/25 g. L. monocytogenes was detected after a 24 hr pre-enrichment, which represents a great improvement over other previously published RPA methods. Additionally, the evaluation of the method reported a Limit of dDetection 50 (LoD₅₀ ) of 6.3 cfu/25 g, along with relative sensitivity, specificity and accuracy values higher than 90%. Finally, the index of kappa concordance was calculated to be 0.93 which is interpreted as "almost complete concordance" between the reference and alternative method. Overall, the described methodology proved to be faster, specific, and as sensitive as other methods based on RPA or real-time PCR. PRACTICAL APPLICATION: The methodology described in this study significantly reduces the detection time of L. monocytogenes, when compared with culture-based methods, and it requires fewer steps than other molecular methods, making it a reliable and more convenient method for routine testing. Finally, the evaluation of the methodology in spiked food samples, confirms its reliability.

Direct and Rapid Detection and Quantification of Oenococcus oeni Cells in Wine by Cells-LAMP and Cells-qLAMP

Fast detection and enumeration of Oenococcus oeni in winemaking are necessary to determine whether malolactic fermentation (MLF) is likely to be performed or not and to decide if the use of a commercial starter is needed. In other wines, however, performing MLF can be detrimental for wine and should be avoided. The traditional identification and quantification of this bacteria using culture-dependent techniques in wine-related matrices require up to 14 days to yield results, which can be a very long time to perform possible enological operations. Loop-mediated isothermal amplification (LAMP) is a novel culture-independent technique that amplifies nucleic acid sequences under isothermal conditions with high specificity and efficiency in less than 1 h with inexpensive equipment. We designed LAMP primers for the specific detection and quantification of O. oeni cells. The developed LAMP method allows O. oeni to be detected directly from both grape musts and wines within 1 h from the time that the LAMP reaction begins, and without DNA extraction and purification requirements. The high sensitivity of LAMP methodology is achieved by previous mechanical cells lysis with no further purification by detecting one single cell per reaction in culture media, and in white/red grape musts and wines by avoiding reaction inhibition by ethanol, polyphenols, and other wine inhibitors. Cells can be concentrated prior to the LAMP reaction to further increase this sensitivity. Moreover, the LAMP method does not require expensive equipment and can be easily operated. The developed method is both economic and fast and offers high sensitivity and specificity.

Loop-Mediated Isothermal Amplification for Salmonella Detection in Food and Feed: Current Applications and Future Directions

Loop-mediated isothermal amplification (LAMP) has become a powerful alternative to polymerase chain reaction (PCR) for pathogen detection in clinical specimens and food matrices. Nontyphoidal Salmonella is a zoonotic pathogen of significant food and feed safety concern worldwide. The first study employing LAMP for the rapid detection of Salmonella was reported in 2005, 5 years after the invention of the LAMP technology in Japan. This review provides an overview of international efforts in the past decade on the development and application of Salmonella LAMP assays in a wide array of food and feed matrices. Recent progress in assay design, platform development, commercial application, and method validation is reviewed. Future perspectives toward more practical and wider applications of Salmonella LAMP assays in food and feed testing are discussed.

Combination of Microfluidic Loop-Mediated Isothermal Amplification with Gold Nanoparticles for Rapid Detection of Salmonella spp. in Food Samples

Foodborne diseases are an important cause of morbidity and mortality. According to the World Health Organization, there are 31 main global hazards, which caused in 2010 600 million foodborne illnesses and 420000 deaths. Among them, Salmonella spp. is one of the most important human pathogens, accounting for more than 90000 cases in Europe and even more in the United States per year. In the current study we report the development, and thorough evaluation in food samples, of a microfluidic system combining loop-mediated isothermal amplification with gold nanoparticles (AuNPs). This system is intended for low-cost, in situ, detection of different pathogens, as the proposed methodology can be extrapolated to different microorganisms. A very low limit of detection (10 cfu/25 g) was obtained. Furthermore, the evaluation of spiked food samples (chicken, turkey, egg products), completely matched the expected results, as denoted by the index kappa of concordance (value of 1.00). The results obtained for the relative sensitivity, specificity and accuracy were of 100% as well as the positive and negative predictive values.