Detection of pathogens in foods: the current state-of-the-art and future directions

Research progress on detection of foodborne pathogens: The more rapid and accurate answer to food safety

In recent years, foodborne diseases have posed a serious threat to human health, and rapid detection of foodborne pathogens is particularly crucial for the prevention and control of such diseases. This article offers a detailed overview of the development of detection techniques for foodborne pathogens, transitioning from traditional microbiological culture methods to the current array of techniques, including immunological, molecular biological, and biosensor-based methods. It summarizes the technical principles, advantages, disadvantages, and research progress of these diverse methods. Furthermore, the article demonstrates that the combination of different methods enhances the efficiency and accuracy of pathogens detection. Specifically, the article focuses on the application and advantages of combining CRISPR/Cas systems with other detection methods in the detection of foodborne pathogens. CRISPR/Cas systems, with their high specificity, sensitivity, and ease of operation, show great potential in the field of foodborne pathogens detection. When integrated with other detection techniques such as immunological detection techniques, molecular biology detection techniques, and biosensors, the accuracy and efficiency of detection can be further improved. By fully utilizing these tools, early detection and control of foodborne diseases can be achieved, enhancing public health and preventing disease outbreaks. This article serves as a valuable reference for exploring more convenient, accurate, and sensitive field detection methods for foodborne pathogens, promoting the application of rapid detection techniques, and ensuring food safety and human health.

Rapid and visual detection of Shiga-toxigenic Escherichia coli (STEC) in carabeef meat harnessing loop-mediated isothermal amplification (LAMP)

Shiga toxigenic E. coli are important foodborne zoonotic pathogens. The present study was envisaged to standardize loop-mediated isothermal amplification assays targeting stx1 and stx2 genes for rapid and visual detection of STEC and compare its sensitivity with PCR. The study also assessed the effect of short enrichment on the detection limit of LAMP and PCR. The developed LAMP assays were found to be highly specific. Analytical sensitivity of LAMP was 94 fg/µLand 25.8 fg/µL for stx-1 and stx-2 while LOD of 5 CFU/g of carabeef was measured after 6-12 h enrichment. The study highlights the importance of short (6-12 h) enrichment for improving the sensitivity of LAMP. The entire detection protocol could be performed within 9 h yielding results on the same day. The developed LAMP assays proved to be a handy and cost-effective alternative for screening STEC contamination in meat.

Development and Application of Four Foodborne Pathogens by TaqMan Multiplex Real-Time PCR

A TaqMan multiplex real-time PCR (mRT-PCR) was developed to detect simultaneously Salmonella spp., Escherichia coli O157, Staphylococcus aureus, and Listeria monocytogenes in food samples. The method involves four sets of primers and probes tailored to the unique DNA sequences found in the invA, nuc, rfbE, and hly genes of each pathogen. The generated standard curves, correlating gene copy numbers with Ct values, demonstrated high accuracy (R2 > 0.99) and efficiency (92%-104%). Meanwhile, the limit of detection was 100 CFU/mL for the four target bacteria in artificially contaminated food samples after 6-8 h of enrichment. The assay's effectiveness was further verified by testing 80 naturally contaminated food samples, showing results largely in agreement with traditional culture methods. Overall, this newly developed TaqMan mRT-PCR, inclusive of a pre-enrichment step, proves to be a dependable and effective tool for detecting single or multiple pathogens in diverse food items, offering significant potential for in vitro diagnostics.

Listeria monocytogenes an Emerging Pathogen: a Comprehensive Overview on Listeriosis, Virulence Determinants, Detection, and Anti-Listerial Interventions

Listeria monocytogenes, the third most deleterious zoonotic pathogen, is a major causative agent of animal and human listeriosis, an infection related to the consumption of contaminated food products. Even though, this pathogen has been responsible for the outbreaks of foodborne infections in the early 1980s, the major outbreaks have been reported during the past two decades. Listeriosis infection in the host is a rare but life-threatening disease with major public health and economic implications. Extensive reports on listeriosis outbreaks are associated with milk and milk products, meat and meat products, and fresh produce. This bacterium can adapt to any environmental and stress conditions, making it a prime causative agent for major foodborne diseases. The pathogen could survive an antibiotic treatment and persist in the host cell, thereby escaping the standard diagnostic practices. The current review strives to provide concise information on the epidemiology, serotypes, and pathogenesis of the L. monocytogenes to decipher the knowledge on the endurance of the pathogen inside the host and food products as a vehicle for Listeria contaminations. In addition, various detection methods for Listeria species from food samples and frontline regimens of L. monocytogenes treatment have also been discussed.

Rapid Isolation of Low-Level Carbapenem-Resistant E. coli from Water and Foods Using Glycan-Coated Magnetic Nanoparticles

Carbapenem-resistant Enterobacterales (CRE) are one of the major global issues needing attention. Among them, carbapenemase-producing (CP) E. coli strains are commonly found in clinical and biological samples. Rapid and cost-effective detection of such strains is critical in minimizing their deleterious impact. While promising progress is being made in rapid detection platforms, separation and enrichment of bacteria are required to ensure the detection of low bacterial counts. The current separation methods, such as centrifugation, filtration, electrophoresis, and immunomagnetic separation, are often tedious, expensive, or ineffective for clinical and biological samples. Further, the extraction and concentration of antimicrobial-resistant bacteria (ARB) are not well documented. Thus, this study assessed the applicability of cost-effective glycan-coated magnetic nanoparticles (gMNPs) for simple and rapid extraction of CP E. coli. The study included two resistant (R)strains: Klebsiella pneumoniae carbapenemase (KPC)-producing E. coli (R: KPC) and New Delhi metallo-β-lactamase (NDM)-producing E. coli (R: NDM). A susceptible E. coli (S) strain was used as a control, a reference bacterium. The gMNPs successfully extracted and concentrated E. coli (R) and E. coli (S) at low concentrations from large volumes of buffer solution, water, and food samples. The gMNPs concentrated up to two and five times their initial concentration for E. coli (R) and E. coli (S) in the buffer solution, respectively. In water and food samples, the concentration of E. coli (S) and E. coli (R) were similar and ranged 1-3 times their initial inoculation. A variation in the concentration from different food samples was seen, displaying the impact of food microstructure and natural microflora. The cost-effective and rapid bacterial cell capture by gMNPs was achieved in 15 min, and its successful binding to the bacterial cells in the buffer solution and food matrices was also confirmed using Transmission Electron Microscopy (TEM). These results show promising applications of gMNPs to extract pathogens and ARB from biological samples.

Cultured Meat Safety Research Priorities: Regulatory and Governmental Perspectives

As with every new technology, safety demonstration is a critical component of bringing products to market and gaining public acceptance for cultured meat and seafood. This manuscript develops research priorities from the findings of a series of interviews and workshops with governmental scientists and regulators from food safety agencies in fifteen jurisdictions globally. The interviews and workshops aimed to identify the key safety questions and priority areas of research. Participants raised questions about which aspects of cultured meat and seafood production are novel, and the implications of the paucity of public information on the topic. Novel parameters and targets may require the development of new analytical methods or adaptation and validation of existing ones, including for a diversity of product types and processes. Participants emphasized that data sharing of these efforts would be valuable, similar to those already developed and used in the food and pharmaceutical fields. Contributions to such databases from the private and public sectors would speed general understanding as well as efforts to make evaluations more efficient. In turn, these resources, combined with transparent risk assessment, will be critical elements of building consumer trust in cultured meat and seafood products.

Detection of Salmonella Enteritidis in Milk Using Conductometric Immunosensor Coated on Polyaniline/Zinc Oxide Nanocomposite

The demand for rapid and accurate detection methods for Salmonella Enteritidis necessitates the development of highly sensitive and specific biosensors to ensure proper monitoring of food safety and quality requirements in the food sector and to secure human health. This study focused on development of a polyaniline/zinc oxide (PANI/ZnO) nanocomposite film on a gold electrode conductometric immunosensor for detection of Salmonella Enteritidis. The sensor was modified with monoclonal anti-Salmonella Enteritidis antibodies as biorecognition elements. The fabricated sensor was able to detect and quantify the target pathogen within 30 min and showed a good detection range from 10¹ to 10⁵ colony-forming units (CFU)/mL for Salmonella Enteritidis and a minimum detection limit of 6.44 CFU/mL in 0.1% peptone water. Additionally, the fabricated sensor showed good selectivity and detection limit toward the target bacterium and successfully determined Salmonella Enteritidis content in ultrahigh heat-treated skim milk samples without pretreatment of the food sample.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

Recent Advances in the Detection of Listeria monocytogenes

Listeria monocytogenes is the third-most severe pathogen causing a yearly outbreak of food poisoning in the world that proliferates widely in the environment. Infants, pregnant mothers, and immuno-compromised people are at high risk. Its ability to grow in both biotic and abiotic environments leads to epidemics that infect 5 out of 10 people annually. Because of the epithelial adhesion (by E-cadherin binding), it can suppress immune cells and thrive in the gastrointestinal tract till the brain through blood flow (E-cadherin). Microbial culture is still used as a gold standard, but takes a long time and often yields false positive results due to incompetence and temperature variations. Therefore, in order to treat it rather than using broad spectrum antibiotics, a standardized time-saving and highly specific technology for early detection is very important. It has been observed that the production of a particular antibody is delaying (so does the detection process) as a result of the inadequate understanding of the pathophysiology of the bacteria. This book chapter provides a brief summary of a pathogen as well as the scientific advances that led to its identification more easily.

Combined antibodies against internalins A and B proteins have potential application in immunoassay for detection of Listeria monocytogenes

Listeria monocytogenes is a food-borne bacterium that causes listeriosis upon the ingestion of contaminated food. Traditional methods to detect L. monocytogenes require pre-enrichment broths to increase its concentration. To improve the screening of contaminated food and prevent listeriosis outbreaks, rapid, specific and sensitive assays are needed to detect L. monocytogenes. This study developed a prototype lateral flow immunochromatographic assay (LFIA) employing antibodies against L. monocytogenes Internalin A (InlA) and Internalin B (InlB) proteins, that are involved in non-phagocytic cell invasion. The following antibodies were used to capture L. monocytogenes antigenic targets: mouse anti-Internalin A monoclonal antibody (MAb-2D12) conjugated to colloidal gold nanoparticles and a mouse anti-Internalin B polyclonal antibody. This test was able to detect pure L. monocytogenes from culture with a limit of detection (LOD) ranging from 5.9 × 103 to 1.5 × 104 CFU/mL. In milk artificially contaminated with L. monocytogenes, the LOD was 1 × 105 CFU/mL. This prototype test discriminated L. monocytogenes from other bacterial species (Listeria innocua, Enterobacter cloacae, Bacillus cereus). Results indicate that this LFIA developed using antibodies against L. monocytogenes InlA and InlB proteins is a sensitive and specific tool that can be potentially useful to rapidly detect L. monocytogenes in contaminated food.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05597-9.

Rapid detection of Salmonella enterica in leafy greens by a novel DNA microarray-based PathogenDx system

The diverse matrices pose great challenges for rapid detection of low Salmonella level (<10 CFU) in fresh produce. The applicability of microarray-based PathogenDx system for detecting low contamination of Salmonella Newport from leafy greens was evaluated. A pre-PCR preparation protocol including enrichment in universal pre-enrichment broth for 3 h followed by sample concentration using an InnovaPrep bio-concentrator or 6 h enrichment without a concentration step was used for detecting S. Newport from leafy greens with initial inoculum level at ∼6 CFU/25 g. Among 205 samples tested, 98%, 93%, 76%, and 60% of Romaine lettuce, Iceberg lettuce, kale, and spinach samples were tested positive after 3 h of enrichment with sample concentration. After 6 h of enrichment, 100%, 98%, 90%, and 82% of Romaine lettuce, Iceberg lettuce, kale, and spinach samples were positive. The samples were parallelly tested by the FDA bacterial analytical manual (BAM) method and 100% of spiked produce samples were tested positive. The overall analysis time of this methodology was between 8 and 11 h, including all pre-enrichment and concentration steps, in contrast to 4-5 days required for BAM method. The system correctly differentiated all 108 Salmonella strains and 35 non-Salmonella strains used in the study. This novel microarray approach provides a rapid method for detecting Salmonella in leafy greens.

Combination of filtration and immunomagnetic separation based on real-time PCR to detect foodborne pathogens in fresh-cut apple

Rapid detection methods require pre-enrichment culture in order to detect low levels of foodborne pathogens. To rapidly detect foodborne pathogens, enrichment culture processes could be replaced. Filtration and immunomagnetic separation methods have been identified to effectively concentrate and separate target pathogens from foods. In this study, a combination of filtration and immunomagnetic separation (IMS) has enabled the rapid and sensitive detection of foodborne pathogens. The pretreatment method, including separation and concentration procedures, increased sensitivity 10-100-fold. The sensitivity of a combination method using filtration and IMS to detect Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium was 10⁰-10¹ CFU/10 mL. In fresh-cut apples, IMS combined with filtration effectively improved the detection limit of real-time PCR to 2.70 × 10¹ CFU/g in E. coli O157:H7 and 1.80 × 10² CFU/g in Salmonella. The filtration simplified processing of large-volumes (250 mL) and effectively concentrated pathogens while decreasing immunomagnetic beads used in IMS. Bacterial concentration by IMS combined with filtration increased sensitivity 10-100-fold compared with control. In addition, the application of IMS effectively removed concentrated residual food material (10-15 mg/mL) after filtration, improving relative sensitivity. In conclusion, this method may detect foodborne pathogen in foods such as fresh-cut fruits in a more rapid and sensitive fashion than traditional culture-based methods.

Listeria monocytogenes in foods-From culture identification to whole-genome characteristics

Listeria monocytogenes is an important foodborne pathogen, which is able to persist in the food production environments. The presence of these bacteria in different niches makes them a potential threat for public health. In the present review, the current information on the classical and alternative methods used for isolation and identification of L. monocytogenes in food have been described. Although these techniques are usually simple, standardized, inexpensive, and are routinely used in many food testing laboratories, several alternative molecular-based approaches for the bacteria detection in food and food production environments have been developed. They are characterized by the high sample throughput, a short time of analysis, and cost-effectiveness. However, these methods are important for the routine testing toward the presence and number of L. monocytogenes, but are not suitable for characteristics and typing of the bacterial isolates, which are crucial in the study of listeriosis infections. For these purposes, novel approaches, with a high discriminatory power to genetically distinguish the strains during epidemiological studies, have been developed, e.g., whole-genome sequence-based techniques such as NGS which provide an opportunity to perform comparison between strains of the same species. In the present review, we have shown a short description of the principles of microbiological, alternative, and modern methods of detection of L. monocytogenes in foods and characterization of the isolates for epidemiological purposes. According to our knowledge, similar comprehensive papers on such subject have not been recently published, and we hope that the current review may be interesting for research communities.

Advances, limitations, and prospects of biosensing technology for detecting phytopathogenic bacteria

Phytopathogenic bacteria cause severe economic losses in agricultural production worldwide. The spread rates, severity, and emerging plant bacterial diseases have become serious threat to the sustainability of food sources and the fruit industry. Detection and diagnosis of plant diseases are imperative in order to manage plant diseases in field conditions, greenhouses, and food storage conditions as well as to maximize agricultural productivity and sustainability. To date, various techniques including, serological, observation-based, and molecular methods have been employed for plant disease detection. These methods are sensitive and specific for genetic identification of bacteria. However, these methods are specific for genetic identification of bacteria. Currently, the innovative biosensor-based disease detection technique is an attractive and promising alternative. A biosensor system involves biological recognition and transducer active receptors based on sensors used in plant-bacteria diagnosis. This system has been broadly used for the rapid diagnosis of plant bacterial pathogens. In the present review, we have discussed the conventional methods of bacterial-disease detection, however, the present review mainly focuses on the applications of different biosensor-based techniques along with point-of-care (POC), robotics, and cell phone-based systems. In addition, we have also discussed the challenges and limitations of these techniques.

Development and Evaluation of a Paper-Based Microfluidic Device for Detection of Listeria monocytogenes on Food Contact and Non-Food Contact Surfaces

Listeria monocytogenes is the third most deadly foodborne pathogen in the United States. The bacterium is found in soil and water, contaminating raw food products and the processing environment, where it can persist for an extended period. Currently, testing of food contact and non-food contact surfaces is performed using an array of sampling devices and endpoint technologies, offering various levels of sensitivity, cost, user skill, and time to detection. Paper-based microfluidic devices (µPADs) are a rapid detection platform amenable to low-cost, user-friendly, and portable diagnostics. In this study, we developed and evaluated a µPAD platform specific for the colorimetric detection of the Listeria genus following recovery from food contact and non-food contact surfaces. For detection, four colorimetric substrates specific for the detection of β-glucosidase, two broths selective for the detection of Listeria spp., and a nonselective broth were evaluated to facilitate detection of Listeria spp. The limit of detection and time to detection were determined by using pure bacterial cultures. After 8 h enrichment, L. monocytogenes (10² Colony Forming Units (CFU)/coupon) was detected on every surface. After 18 h enrichment, L. monocytogenes (10² CFU/coupon) was detected on all surfaces with all swabbing devices. This study demonstrated the ability of the µPAD-based method to detect potentially stressed cells at low levels of environmental contamination.

Current Methods for Extraction and Concentration of Foodborne Bacteria with Glycan-Coated Magnetic Nanoparticles: A Review

Rapid and accurate food pathogen detection is an essential step to preventing foodborne illnesses. Before detection, removal of bacteria from the food matrix and concentration to detectable levels are often essential steps. Although many reviews discuss rapid concentration methods for foodborne pathogens, the use of glycan-coated magnetic nanoparticles (MNPs) is often omitted. This review seeks to analyze the potential of this technique as a rapid and cost-effective solution for concentration of bacteria directly from foods. The primary focus is the mechanism of glycan-coated MNP binding, as well as its current applications in concentration of foodborne pathogens. First, a background on the synthesis, properties, and applications of MNPs is provided. Second, synthesis of glycan-coated particles and their theorized mechanism for bacterial adhesion is described. Existing research into extraction of bacteria directly from food matrices is also analyzed. Finally, glycan-coated MNPs are compared to the magnetic separation technique of immunomagnetic separation (IMS) in terms of cost, time, and other factors. At its current state, glycan-coated MNPs require more research to fully identify the mechanism, potential for optimization, and extraction capabilities directly in food matrices. However, current research indicates glycan-coated MNPs are an incredibly cost-effective method for rapid food pathogen extraction and concentration.

Advances in Chicken IgY-Based Immunoassays for the Detection of Chemical and Biological Hazards in Food Samples

As antibodies are the main biological binder for hazards in food samples, their performance directly determines the sensitivity, specificity, and reproducibility of the developed immunoassay. The overwhelmingly used mammalian-derived antibodies usually suffer from complicated preparation, high cost, frequent bleeding of animals, and sometimes low titer and affinity. Chicken yolk antibody (IgY) has recently attracted considerable attention in the bioanalytical field owing to its advantages in productivity, animal welfare, comparable affinity, and high specificity. However, a broad understanding of the application of IgY-based immunoassay for the detection of chemical and biological hazards in food samples remains limited. Here, we briefly summarized the diversity, structure, and production of IgY including polyclonal and monoclonal formats. Then, a comprehensive overview of the principles, designs, and applications of IgY-based immunoassays for these hazards was reviewed and discussed, including food-borne pathogens, food allergens, veterinary drugs, pesticides, toxins, endocrine disrupting chemicals, etc. Thus, the trend of IgY-based immunoassays is expected, and more IgY types, higher sensitivity, and diversification of recognition-to-signal manners are necessary in the future.

Loop-mediated isothermal amplification (LAMP): a sensitive molecular tool for detection of Staphylococcus aureus in meat and dairy product

Staphylococcus aureus-mediated food poisoning is a primary concern worldwide. The presence of the organism in food is an indicative of poor sanitation during production, and it is essential to have efficient methods for detecting this pathogen. A novel molecular diagnostic technique called loop-mediated isothermal amplification (LAMP) serves as a rapid and sensitive detection method, which amplifies nucleic acids at isothermal conditions. In this study, a LAMP-based diagnostic assay was developed to detect Staphylococcus aureus (S. aureus) using two target genes femA and arcC. The optimum reaction temperature was found to be 65 °C and at 60 °C for femA and arcC genes, respectively. The developed assay specifically amplified DNA from S. aureus, not from other related bacterial species and compared to PCR, and a 100-fold higher sensitivity was observed. Furthermore, the LAMP assay could detect the pathogen from food samples mainly meat and dairy samples when analyzed in both intact and enriched conditions. Thirteen samples were found positive for S. aureus with LAMP showing a greater number of positive samples in comparison to PCR. This study established a highly sensitive and a rapid diagnostic procedure for the detection and surveillance of this major foodborne pathogen.

Simultaneous Detection of Four Main Foodborne Pathogens in Ready-to-Eat Food by Using a Simple and Rapid Multiplex PCR (mPCR) Assay

The increasing consumption of organic or ready-to-eat food may cause serious foodborne disease outbreaks. Developing microbiological culture for detection of food-borne pathogens is time-consuming, expensive, and laborious. Thus, alternative methods such as polymerase chain reaction (PCR) are usually employed for outbreaks investigation. In this work, we aimed to develop a rapid and simple protocol for the simultaneous detection of Escherichia coli (E coli), Listeria monocytogenes (L. monocytogenes), Staphylococcus aureus (S. aureus) and Salmonella enterica (S. enterica), by the combination of an enrichment step in a single culture broth and a multiplex PCR (mPCR) assay. The effectiveness of several enrichment media was assessed by culture and PCR. Buffered peptone water (BPW) was selected as the optimum one. Then, mPCR conditions were optimized and applied both to pure co-cultures and artificially inoculated food samples (organic lettuce and minced meat). In the culture medium inoculated at 10⁰ CFU/mL, mPCR was able to detect the four microorganisms. When performed on artificially food samples, the mPCR assy was able to detect E. coli, S. enterica, and L. monocytogenes. In conclusion, BPW broth can effectively support the simultaneous growth of E. coli, S. aureus, L. monocytogenes, and S. enterica and could be, thus, used prior to a mPCR detection assay in ready-to-eat food, thereby considerably reducing the time, efforts and costs of analyzes.

Next-Generation Food Research: Use of Meta-Omic Approaches for Characterizing Microbial Communities Along the Food Chain

Microorganisms exist along the food chain and impact the quality and safety of foods in both positive and negative ways. Identifying and understanding the behavior of these microbial communities enable the implementation of preventative or corrective measures in public health and food industry settings. Current culture-dependent microbial analyses are time-consuming and target only specific subsets of microbes. However, the greater use of culture-independent meta-omic approaches has the potential to facilitate a thorough characterization of the microbial communities along the food chain. Indeed, these methods have shown potential in contributing to outbreak investigation, ensuring food authenticity, assessing the spread of antimicrobial resistance, tracking microbial dynamics during fermentation and processing, and uncovering the factors along the food chain that impact food quality and safety. This review examines the community-based approaches, and particularly the application of sequencing-based meta-omics strategies, for characterizing microbial communities along the food chain. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Multifunctional magnetic nanoparticle cloud assemblies for in situ capture of bacteria and isolation of microbial DNA

We investigate the formation of suspended magnetic nanoparticle (MNP) assemblies (M-clouds) and their use for in situ bacterial capture and DNA extraction. M-clouds are obtained as a result of magnetic field density variations when magnetizing an array of micropillars coated with a soft ferromagnetic NiP layer. Numerical simulations suggest that the gradient in the magnetic field created by the pillars is four orders of magnitude higher than the gradient generated by the external magnets. The pillars therefore serve as the sole magnetic capture sites for MNPs which accumulate on opposite sides of each pillar facing the magnets. Composed of loosely aggregated MNPs, the M-cloud can serve as a porous capture matrix for target analyte flowing through the array. The concept is demonstrated by using a multifunctional M-cloud comprising immunomagnetic NPs (iMNPs) for capture of Escherichia coli O157:H7 from river water along with silica-coated NPs for subsequent isolation and purification of microbial DNA released upon bacterial lysis. Confocal microscopy imaging of fluorescently labeled iMNPs and E. coli O157:H7 reveals that bacteria are trapped in the M-cloud region between micropillars. Quantitative assessment of in situ bacterial capture, lysis and DNA isolation using real-time polymerase chain reaction shows linear correlation between DNA output and input bacteria concentration, making it possible to confirm E. coli 0157:H7 at 10³ cells per mL. The M-cloud method further provides one order of magnitude higher DNA output concentrations than incubation of the sample with iMNPs in a tube for an equivalent period of time (e.g., 10 min). Results from assays performed in the presence of Listeria monocytogenes (at 10⁶ cells per mL each) suggest that non-target organisms do not affect on-chip E. coli capture, DNA extraction efficiency and quality of the eluted sample.

Identification of a specific surface epitope of OmpC for Escherichia coli O157:H7 with protein topology facilitated affinity mass spectrometry

Abstract

The goal of this work was to identify the target protein and epitope of a previously reported Escherichia coli O157:H7 (ECO157)–specific monoclonal antibody (mAb) 2G12. mAb 2G12 has shown high specificity for the recovery and detection of ECO157. To achieve this goal, the target protein was first separated by two-dimensional gel electrophoresis (2-DE) and located by Western blot (WB). The protein spots were identified to be the outer membrane protein (Omp) C by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF–MS). After that, the target protein was purified by immunoaffinity chromatography (IAC) and subjected to in situ enzymatic cleavage of the vulnerable peptides. Eight eluted peptides of OmpC identified by liquid chromatography–tandem mass spectrometry (LC–MS/MS) were further mapped onto the homologous protein structure of E. coli OmpC (2IXX). The topology of OmpC showed that three peptides had extracellular loops. Epitope mapping with overlapping peptide library and sequence homology analysis revealed that the epitope consisted of a specific peptide, “LGVING,” and an adjacent conservative peptide, “TQTYNATRVGSLG.” Both peptides loop around the overall structure of the epitope. To test the availability of the epitope when ECO157 was grown under different osmolarity, pH, and nutrition levels, the binding efficacy of mAb 2G12 with ECO157 grown in these conditions was evaluated. Results further demonstrated the good stability of this epitope under potential stressful environmental conditions. In summary, this study revealed that mAb 2G12 targeted one specific and one conservative extracellular loop (peptide) of the OmpC present on ECO157, and the epitope was stable and accessible on ECO157 cells grown in different environment.

Key points

• OmpC is the target of a recently identified ECO157-specific mAb 2G12.

• Eight peptides were identified from the OmpC by using LC–MS/MS.

• The specificity of mAb 2G12 is mainly determined by the “LGVING” peptide.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11511-8.

Culture-free biphasic approach for sensitive detection of Escherichia coli O157:H7 from beef samples

Foodborne illnesses are a major threat to public health also leading to significant mortality and financial and reputational damage to industry. It is very important to detect pathogen presence in food products early, rapidly, and accurately to avoid potential outbreaks and economic loss. However, "gold standard" culture methods, including enrichment of pathogens, can take up to several days. Moreover, the food matrix often interferes with nucleic acid amplification methods of detection, requiring DNA extraction from the sample for successful molecular detection of pathogens. Here, we introduce a "biphasic" amplification method that can achieve high sensitivity detection with background noise from ground beef food samples without culture or other extraction methods in 2.5 h. Homogenized ground beef is dried resulting in an increase in porosity of the dried food matrix to allowing amplification enzymes and primers to access the target DNA and initiate the reaction within the dried food matrix. Using Loop Mediated Isothermal Amplification, we demonstrate the detection of 1-3 cfu of Escherichia coli bacteria in 30 mg of dried food matrix. Our approach significantly lowers the time to result to less than a few hours and have a pronounced impact on reduction of instrumentation complexity and costs.

Validation and Optimization of qPCR Method for Identification of Actaea racemosa (Black Cohosh) NHPs

BACKGROUND

Actaea racemosa (black cohosh) herbal dietary supplements are commonly used to treat menopausal symptoms in women. However, there is a considerable risk of contamination of A. racemosa herbal products in the natural health product (NHP) industry, impacting potential efficacy. Authentication of A. racemosa products is challenging because of the standard, multi-part analytical chemistry methods that may be too costly and not appropriate for both raw and finished products.

OBJECTIVE

In this paper, we discuss developing and validating quick alternative biotechnology methods to authenticate A. racemosa herbal dietary supplements, based on the use of a species-specific hydrolysis PCR probe assay.

METHODS

A qPCR-based species-specific hydrolysis probe assay was designed, validated, and optimized for precisely identifying the species of interest using the following analytical validation criteria: (1) specificity (accuracy) in determining the target species ingredient, while not identifying other non-target species; (2) sensitivity in detecting the smallest amount of the target material; and (3) reliability (repeatability and reproducibility) in detecting the target species in raw materials on a real-time PCR platform.

RESULTS

The results show that the species-specific hydrolysis probe assay was successfully developed for the raw materials and powders of A. racemosa. The specificity of the test was 100% to the target species. The efficiency of the assay was observed to be 99%, and the reliability of the assay was 100% for the raw/starting and powder materials.

CONCLUSION

The method developed in this study can be used to authenticate and perform qualitative analysis of A. racemosa supplements.

Recent Advances in Antifouling Materials for Surface Plasmon Resonance Biosensing in Clinical Diagnostics and Food Safety

Strategies to develop antifouling surface coatings are crucial for surface plasmon resonance (SPR) sensing in many analytical application fields, such as detecting human disease biomarkers for clinical diagnostics and monitoring foodborne pathogens and toxins involved in food quality control. In this review, firstly, we provide a brief discussion with considerations about the importance of adopting appropriate antifouling materials for achieving excellent performances in biosensing for food safety and clinical diagnosis. Secondly, a non-exhaustive landscape of polymeric layers is given in the context of surface modification and the mechanism of fouling resistance. Finally, we present an overview of some selected developments in SPR sensing, emphasizing applications of antifouling materials and progress to overcome the challenges related to the detection of targets in complex matrices relevant for diagnosis and food biosensing.

Choice of 16S ribosomal RNA primers affects the microbiome analysis in chicken ceca

We evaluated the effect of applying different sets of 16S rRNA primers on bacterial composition, diversity, and predicted function in chicken ceca. Cecal contents from Ross 708 birds at 1, 3, and 5 weeks of age were collected for DNA isolation. Eight different primer pairs targeting different variable regions of the 16S rRNA gene were employed. DNA sequences were analyzed using open-source platform QIIME2 and the Greengenes database. PICRUSt2 was used to determine the predicted function of bacterial communities. Changes in bacterial relative abundance due to 16S primers were determined by GLMs. The average PCR amplicon size ranged from 315 bp (V3) to 769 bp (V4–V6). Alpha- and beta-diversity, taxonomic composition, and predicted functions were significantly affected by the primer choice. Beta diversity analysis based on Unweighted UniFrac distance matrix showed separation of microbiota with four different clusters of bacterial communities. Based on the alpha- and beta-diversity and taxonomic composition, variable regions V1–V3(1) and (2), and V3–V4 and V3–V5 were in most consensus. Our data strongly suggest that selection of particular sets of the 16S rRNA primers can impact microbiota analysis and interpretation of results in chicken as was shown previously for humans and other animal species.

Enhanced antibacterial activity of eugenol-entrapped casein nanoparticles amended with lysozyme against gram-positive pathogens

This study aimed to investigate the antibacterial efficiency and synergistic mechanisms of novel formulated eugenol-casein-lysozyme nanoparticles (ECL-NPs) against gram-positive bacteria. We obtained optimized ECL-NPs 151.9 nm in size and with an entrapment efficiency of 92.2%. ECL-NPs exhibited a satisfactory slow-release pattern, excellent storage stability (for 180 days at 4 °C), and freeze-drying stability. The synergy of low-dose lysozyme significantly enhanced the inhibitory efficiency of eugenol-casein nanoparticles against Staphylococcus aureus and Bacillus sp. by 5.83-fold and 5.53-fold, respectively; this resulted in a much lower minimum inhibitory concentration (3.75-fold and 4.16-fold) and minimum bacterial concentration (2.92-fold and 1.70-fold) values. Scanning electron microscopy clearly demonstrated that the entire cell morphological structure was broken into pieces after exposure to ECL-NPs. Furthermore, 100% microbial inhibition was observed in fresh fruits treated with ECL-NPs for 15 days. These findings suggest that ECL-NPs have an excellent potential for use in food industry against gram-positive bacteria.

Rapid detection and discrimination of food-related bacteria using IR-microspectroscopy in combination with multivariate statistical analysis

Spoilage microorganisms are of great concern for the food industry. While traditional culturing methods for spoilage microorganism detection are laborious and time-consuming, the development of early detection methods has gained a lot of interest in the last decades. In this work a rapid and non-destructive detection and discrimination method of eight important food-related microorganisms (Bacillus subtilis DSM 10, Bacillus coagulans DSM 1, Escherichia coli K12 DSM 498, Escherichia coli TOP10, Micrococcus luteus DSM 20030, Pseudomonas fluorescens DSM 4358, Pseudomonas fluorescens DSM 50090 and Bacillus thuringiensis israelensis DSM 5724) based on IR-microspectroscopy and chemometric evaluation was developed. Sampling was carried out directly from the surface to be tested, without the need for sample preparation such as purification, singulation, centrifugation and washing steps, as an efficient and inexpensive blotting technique using the sample carrier. IR spectra were recorded directly after the blotting from the surface of the sample carrier without any further pretreatments. A combination of data preprocessing, principal component analysis and canonical discriminant analysis was found to be suitable. The spectral range from 400 to 1750 cm^-1 of the IR-microspectrosopic data was determined to be highly sensitive to the time after incubation and sample thickness, resulting in a high standard deviation. Therefore, this area was excluded from the evaluation in favor of the meaningfulness of the chemometric model and, thus, only the spectral range of specific -CH/-NH/-OH excitations (2815-3680 cm^-1) was used for model development. This study showed that the differentiation of food-related microorganisms on genera, species and strain level is feasible. A leave-one-out cross-validation of the training data set showed 100% accuracy. The classification of the ungrouped test data showed with an accuracy of 94.5% that, despite the large biological variance of the analytes such as different times after incubation and the presented sampling (including its variance), a robust and meaningful model for the differentiation of food-related bacteria could be developed by data preprocessing and subsequent chemometric evaluation.

Immunomagnetic separation: An effective pretreatment technology for isolation and enrichment in food microorganisms detection

The high efficiency and accurate detection of foodborne pathogens and spoilage microorganisms in food are a task of great social, economic, and public health importance. However, the contamination levels of target bacteria in food samples are very low. Owing to the background interference of food ingredients and negative impact of nontarget flora, the establishment of efficient pretreatment techniques is very crucial for the detection of food microorganisms. With the significant advantages of high specificity and great separation efficiency, immunomagnetic separation (IMS) assay based on immunomagnetic particles (IMPs) has been considered as a powerful system for the separation and enrichment of target bacteria. This paper mainly focuses on the development of IMS as well as their application in food microorganisms detection. First, the basic principle of IMS in the concentration of food bacteria is presented. Second, the effect of different factors, including the sizes of magnetic particles (MPs), immobilization of antibody and operation parameters (the molar ratio of antibody to MPs, the amount of IMPs, incubation time, and bacteria concentration) on the immunocapture efficiency of IMPs are discussed. The performance of IMPs in different food samples is also evaluated. Finally, the combination of IMS and various kinds of detection methods (immunology-based methods, nucleic acid-based methods, fluorescence methods, and biosensors) to detect pathogenic and spoilage organisms is summarized. The challenges and future trends of IMS are also proposed. As an effective pretreatment technique, IMS can improve the detection sensitivity and shorten their testing time, thus exhibiting broad prospect in the field of food bacteria detection.

Supplementing resuscitation-promoting factor (Rpf) enhanced biodegradation of polychlorinated biphenyls (PCBs) by Rhodococcus biphenylivorans strain TG9T

The biodegradation of polychlorinated biphenyls (PCBs) occurs slowly when the degrading bacteria enter a low activity state, such as a viable but nonculturable (VBNC) state, under unfavorable environmental conditions. The introduction of resuscitation-promoting factor (Rpf) can re-activate VBNC bacteria. This study tested the feasibility of enhancing PCB biodegradation via supplementing Rpf in liquid culture and soil microcosms inoculated with Rhodococcus biphenylivorans strain TG9^T. Exogenous Rpf resuscitated TG9^T cells that had previously entered the VBNC state after 90 d of nutrient starvation, resulting in the significantly enhanced degradation of PCB by 24.3% over 60 h in liquid medium that originally contained 50 mg L^-1 Aroclor 1242. In soil microcosms containing 50 mg kg^-1 Aroclor 1242 and inoculated with VBNC TG9^T cells, after 49 d of supplementation with Rpf, degradation efficiency of PCB reached 34.2%, which was significantly higher than the control. Our results confirmed that exogenous Rpf resuscitated VBNC TG9^T cells by stimulating endogenous expression of rpf gene orthologs. The enhanced PCB-degrading capability was likely due to the increased cell numbers and the strong expression of PCB catabolic genes. This study demonstrated the role of Rpf in enhancing PCB degradation via resuscitating PCB-degrading bacteria, indicating a promising approach for the remediation of PCB contamination.

From hazard analysis to risk control using rapid methods in microbiology: A practical approach for the food industry

The prevention of foodborne diseases is one of the main objectives of health authorities. To this effect, analytical techniques to detect and/or quantify the microbiological contamination of foods prior to their release onto the market are required. Management and control of foodborne pathogens have generally been based on conventional detection methodologies, which are not only time-consuming and labor-intensive but also involve high consumable materials costs. However, this management perspective has changed over time given that the food industry requires efficient analytical methods that obtain rapid results. This review covers the historical context of traditional methods and their passage in time through to the latest developments in rapid methods and their implementation in the food sector. Improvements and limitations in the detection of the most relevant pathogens are discussed from a perspective applicable to the current situation in the food industry. Considering efforts that are being done and recent developments, rapid and accurate methods already used in the food industry will be also affordable and portable and offer connectivity in near future, which improves decision-making and safety throughout the food chain.

Novel surface plasmon resonance biosensor that uses full-length Det7 phage tail protein for rapid and selective detection of Salmonella enterica serovar Typhimurium

We report a novel surface plasmon resonance (SPR) biosensor that uses the full-length Det7 phage tail protein (Det7T) to rapidly and selectively detect Salmonella enterica serovar Typhimurium (S. Typhimurium). Det7T, which was obtained using recombinant protein expression and purification in Escherichia coli, demonstrated a size of ∼75 kDa upon SDS-PAGE and was homotrimeric in its native structure. Microagglutination and transmission electron microscopy (TEM) data revealed that the protein specifically bound to the host, S. Typhimurium, but not to nonhost E. coli K-12 cells. The observed protein agglutination occurred over a concentration range of 0.8-24.6 µg/mL. The Det7T proteins were immobilized on gold-coated surfaces using amine-coupling to generate a novel Det7T-functionalized SPR biosensor, wherein the specific binding of these proteins with bacteria was detected by SPR. We observed rapid detection of (∼20 Min) and typical binding kinetics with S. Typhimurium in the range of 5 × 10⁴ -5 × 10⁷  CFU/mL, but not with E. coli at any tested concentration, indicating that the sensor exhibited recognition specificity. Similar binding was observed with 10% apple juice spiked with S. Typhimurium, suggesting that this strategy provides promise for the rapid, real-time, and selective monitoring of target microorganisms in the environment, and thus has great potential for supporting health by enabling early disease prevention.

Colorimetric Detection of Escherichia coli O157:H7 with Signal Enhancement Using Size-Based Filtration on a Finger-Powered Microfluidic Device

Although immunomagnetic separation is a useful sample pretreatment method that can be used to separate target pathogens from a raw sample, it is challenging to remove unbound free magnetic nanoparticles (MNPs) for colorimetric detection of target pathogens. Here, size-based filtration was exploited for the rapid on-site detection of pathogens separated by immunomagnetic separation in order to remove unbound free MNPs using a finger-powered microfluidic device. A membrane filter and an absorbent pad were integrated into the device and a mixture of unbound free MNPs and MNP-bound Escherichia coli (E. coli) O157:H7 was dispensed over the membrane filter by pressing and releasing the pressure chamber. A colorimetric signal was generated by MNP-bound E. coli O157:H7 while unbound free MNPs were washed out by the absorbent. Furthermore, the colorimetric signals can be amplified using a gold enhancer solution when gold-coated MNPs were used instead of MNPs. As a result, 10² CFU/mL E. coli O157:H7 could be detected by the enhanced colorimetric signal on a proposed device.

High Resolution Melt Assays to Detect and Identify Vibrio parahaemolyticus, Bacillus cereus, Escherichia coli, and Clostridioides difficile Bacteria

Over one hundred bacterial species have been determined to comprise the human microbiota in a healthy individual. Bacteria including Escherichia coli, Bacillus cereus, Clostridioides difficile, and Vibrio parahaemolyticus are found inside of the human body and B. cereus and E. coli are also found on the skin. These bacteria can act as human pathogens upon ingestion of contaminated food or water, if they enter an open wound, or antibiotics, and environment or stress can alter the microbiome. In this study, we present new polymerase chain reaction (PCR) high-resolution melt (HRM) assays to detect and identify the above microorganisms. Amplified DNA from C. difficile, E. coli, B. cereus, and V. parahaemolyticus melted at 80.37 ± 0.45 °C, 82.15 ± 0.37 °C, 84.43 ± 0.50 °C, and 86.74 ± 0.65 °C, respectively. A triplex PCR assay was developed to simultaneously detect and identify E. coli, B. cereus, and V. parahaemolyticus, and cultured microorganisms were successfully amplified, detected, and identified. The assays demonstrated sensitivity, specificity, reproducibility, and robustness in testing.

Construction and application of carbohydrate microarrays to detect foodborne bacteria

The rapid detection of pathogenic bacteria is vital for the prevention of outbreaks of infectious diseases, including infections by the common foodborne bacteria E.coli and Salmonella Carbohydrate microarrays have been developed as a powerful method to investigate carbohydrate-protein interaction with only very small amounts of glycans, which show great potential for detect the carbohydrate mediated interaction with pathogens. Here, different mannose-coated microarrays were constructed and tested with E.coli (K-12 and BL-21) and Salmonella enterica strains (ATCC9184 and ATCC31685) exhibiting different mannose binding affinities. The optimized carbohydrate microarray was then applied to test the binding of 12 Salmonella enterica and 9 E.coli isolates from local patients for the first time and showed strong binding with certain serovars or subtypes. The results showed that microarray probed with the single mannose structure is not enough for the detection of bacteria with various serovars or subtypes, which contain a high degree of allelic variation in adhesin. We suggest that a complex carbohydrate microarray containing different glycan conformation may be needed for detection of different bacteria isolates.

Combined Enrichment and Quantitative Polymerase Chain Reaction to Improve Sensitivity and Reduce Time of Detection of Listeria monocytogenes in Mushrooms

This study evaluated a combined method for the detection of Listeria monocytogenes in mushrooms, involving enrichment and quantitative real-time polymerase chain reaction (qPCR), to improve sensitivity and reduce detection time. The growth of L. monocytogenes was evaluated in Listeria enrichment broth (LEB) with modified carbon and nitrogen sources, increasing sodium concentrations, and added micronutrients. Primers targeting the L. monocytogenes iap (iap1 and iap2), hlyA (hlyA1-hlyA6), and prfA (prfA1-prfA4) genes were developed and their sensitivity and specificity were evaluated. The greatest increase in L. monocytogenes cell count was observed after 6-h incubation at 30°C in LEB+2 × FAC (LEB plus 20 mL/L ferric ammonium citrate), where cell count increased by 1.4 log CFU (colony-forming unit)/mL, compared with 0.9 log CFU/mL in LEB (p < 0.05). iap2 primers targeting the iap gene showed high specificity and were the most sensitive among those tested, with a detection limit of 2 log CFU/mL in LEB medium, 3.1 log CFU/g in golden needle mushroom, and 3.5 log CFU/g in large oyster mushroom. When applied to detection in golden needle mushrooms, a combination of 3-h incubation in LEB+2 × FAC medium and qPCR analysis with iap2 primers permitted detection of L. monocytogenes, even at an inoculum of 1 log CFU/g. Similarly, in large oyster mushrooms, 10-h enrichment in LEB+2 × FAC medium resulted in a cell count of 3.7 log CFU/g. These results indicate that a combined detection method, using LEB+2 × FAC medium for enrichment followed by qPCR with iap2 primer pair, can reduce enrichment time and improve the sensitivity and specificity of L. monocytogenes detection in mushrooms.

High Throughput Sequencing Technologies as a New Toolbox for Deep Analysis, Characterization and Potentially Authentication of Protection Designation of Origin Cheeses?

Protected Designation of Origin (PDO) labeling of cheeses has been established by the European Union (EU) as a quality policy that assures the authenticity of a cheese produced in a specific region by applying traditional production methods. However, currently used scientific methods for differentiating and establishing PDO are limited in terms of time, cost, accuracy and their ability to identify through quantifiable methods PDO fraud. Cheese microbiome is a dynamic community that progressively changes throughout ripening, contributing via its metabolism to unique qualitative and sensorial characteristics that differentiate each cheese. High Throughput Sequencing (HTS) methodologies have enabled the more precise identification of the microbial communities developed in fermented cheeses, characterization of their population dynamics during the cheese ripening process, as well as their contribution to the development of specific organoleptic and physio-chemical characteristics. Therefore, their application may provide an additional tool to identify the key microbial species that contribute to PDO cheeses unique sensorial characteristics and to assist to define their typicityin order to distinguish them from various fraudulent products. Additionally, they may assist the cheese-makers to better evaluate the quality, as well as the safety of their products. In this structured literature review indications are provided on the potential for defining PDO enabling differentiating factors based on distinguishable microbial communities shaped throughout the ripening procedures associated to cheese sensorial characteristics, as revealed through metagenomic and metatranscriptomic studies. Conclusively, HTS applications, even though still underexploited, have the potential to demonstrate how the cheese microbiome can affect the ripening process and sensorial characteristics formation via the catabolism of the available nutrients and interplay with other compounds of the matrix and/or production of microbial origin metabolites and thus their further quality enhancement.

Point-of-Care Strategies for Detection of Waterborne Pathogens

Waterborne diseases that originated due to pathogen microorganisms are emerging as a serious global health concern. Therefore, rapid, accurate, and specific detection of these microorganisms (i.e., bacteria, viruses, protozoa, and parasitic pathogens) in water resources has become a requirement of water quality assessment. Significant research has been conducted to develop rapid, efficient, scalable, and affordable sensing techniques to detect biological contaminants. State-of-the-art technology-assisted smart sensors have improved features (high sensitivity and very low detection limit) and can perform in a real-time manner. However, there is still a need to promote this area of research, keeping global aspects and demand in mind. Keeping this view, this article was designed carefully and critically to explore sensing technologies developed for the detection of biological contaminants. Advancements using paper-based assays, microfluidic platforms, and lateral flow devices are discussed in this report. The emerging recent trends, mainly point-of-care (POC) technologies, of water safety analysis are also discussed here, along with challenges and future prospective applications of these smart sensing technologies for water health diagnostics.

Subnanomolar FRET-Based DNA Assay Using Thermally Stable Phosphorothioated DNA-Functionalized Quantum Dots

Quantum dots (QDs) can serve as an attractive Förster resonance energy transfer (FRET) donor for DNA assay due to their excellent optical properties. However, the specificity and sensitivity of QD-based FRET analysis are prominently reduced by nonspecific DNA adsorption and poor colloidal stability during DNA hybridization, which hinders the practical applications of QDs as a biosensing platform. Here, we report subnanomolar FRET assay of DNA through the stabilization of DNA/QD interface using DNA-functionalized QDs with phosphorothioated single-stranded DNA (pt-ssDNA) as a multivalent ligand in an aqueous solution. In situ DNA functionalization was achieved during the aqueous synthesis of CdTe/CdS QDs, resulting in the maximum photoluminescence quantum yields of 76.9% at an emission wavelength of 732 nm. Conventional monothiolated ssDNA-capped QDs exhibited particle aggregation and photoluminescence (PL) quenching during DNA hybridization at 70 °C due to the dissociation of surface ligands. Such colloidal instability induced the nonspecific adsorption of DNA, resulting in false-positive signal and decreased sensitivity with the limit of detection (LOD) of 16.1 nM. In contrast, the pt-ssDNA-functionalized QDs maintained their colloidal stability and PL properties at elevated temperatures. The LOD of the pt-ssDNA-functionalized QDs was >30 times lower (0.47 nM) while maintaining the high specificity to a target sequence because the strong multivalent binding of pt-ssDNA to the surface of QDs prevents the detachment of pt-ssDNA and nonspecific adsorption of DNA. The study suggests that the ligand design to stabilize the surface of QDs in an aqueous milieu is critically important for the high performance of QDs for specific DNA assay.

Multiplex touchdown PCR assay to enhance specificity and sensitivity for concurrent detection of four foodborne pathogens in raw milk

AIMS

The aim of this study was to develop a multiplex touchdown PCR (multiplex TD-PCR) for rapid and simultaneous detection of four major foodborne pathogens to avoid mispriming and unwanted production during gene amplification. Touchdown PCR is the modified form of standard PCR, which enhances specificity, sensitivity.

METHODS AND RESULTS

For this reason, a multiplex TD-PCR assay with a pre-enrichment step was developed to detect four foodborne pathogens namely Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica serovar Enteritidis in pure culture and raw milk samples. The results showed that this protocol can eliminate the unwanted band or reduce significantly. The detection sensitivity of the single and multiplex TD-PCR was one cell per ml in pure culture. Furthermore, the detection limit of multiplex TD-PCR was one cell per 25 ml for artificially contaminated raw milk. We obtained similar results for detection of aforementioned pathogens in raw milk, after comparing the multiplex TD-PCR method with the traditional culture, except in one or two samples.

CONCLUSIONS

Hence, the proposed multiplex TD-PCR method could be confirmed as an effective way for rapid optimization of PCR reactions to increase specificity, sensitivity during gene amplification.

SIGNIFICANCE AND IMPACT OF THE STUDY

Hence, due to its simplicity, cost-effectiveness and being time-saving, it seems that this method is reasonable and economical for rapid optimization of PCR reactions.

Developing a multiplex real-time PCR with a new pre-enrichment to simultaneously detect four foodborne bacteria in milk

Aim: The aim of this study is to formulate a new single nonselective pre-enrichment medium (ELSS) that can support the concurrent growth of four major foodborne pathogens containing E. coli O157: H7, L. monocytogenes, S. aureus and S. enterica serovar Entertidis to develop a multiplex TaqMan Real-time PCR (mRT-PCR). Methods: The mRT-PCR with a new pre-enrichment was carried out for simultaneous detection and quantification of these foodborne bacteria. Results: By using mRT-PCR after 16 h pre-enrichment in ELSS, the detection limit of each pathogen was 1 CFU/25 ml contaminated milk, as well as inclusivity and exclusivity reached 100%. Conclusion: The mRT-PCR assay with pre-enrichment step is a fast and reliable technique for detecting single or multiple pathogens in food products.