Nano/micro and spectroscopic approaches to food pathogen detection

Current State of Development of Biosensors and Their Application in Foodborne Pathogen Detection

ABSTRACT

Foodborne disease outbreaks continue to be a major public health and food safety concern. Testing products promptly can protect consumers from foodborne diseases by ensuring the safety of food before retail distribution. Fast, sensitive, and accurate detection tools are in great demand. Therefore, various approaches have been explored recently to find a more effective way to incorporate antibodies, oligonucleotides, phages, and mammalian cells as signal transducers and analyte recognition probes on biosensor platforms. The ultimate goal is to achieve high specificity and low detection limits (1 to 100 bacterial cells or piconanogram concentrations of toxins). Advancements in mammalian cell-based and bacteriophage-based sensors have produced sensors that detect low levels of pathogens and differentiate live from dead cells. Combinations of biotechnology platforms have increased the practical utility and application of biosensors for detection of foodborne pathogens. However, further rigorous testing of biosensors with complex food matrices is needed to ensure the utility of these sensors for point-of-care needs and outbreak investigations.

HIGHLIGHTS

Advances in differentiation and identification of foodborne bacteria using near infrared spectroscopy

Rapid and sensitive detection of foodborne bacteria is a growing concern for ensuring safe food supply and preventing human foodborne infections. It is difficult for conventional methods to meet these detection requirements because they are often tedious and time-consuming. In the recent years, near infrared (NIR) spectroscopy has been found to be a promising method for all sorts of analyses in microbiology due to its highly specific absorption signature and non-destructive measurements. In this review, we first briefly introduce the fundamental and basic operational procedure of NIR spectroscopy for foodborne bacteria detection. Then we summarize the main advances and contributions of this technique in the study of foodborne bacteria. Finally, we conclude that much work still remains to be done before NIR spectroscopy really becomes a viable alternative in the field of microbiological characterization.

Three Dimensional Vero Cell-Platform for Rapid and Sensitive Screening of Shiga-Toxin Producing Escherichia coli

Shiga-toxin producing Escherichia coli (STEC) is a serious public health concern. Current Vero cell assay, although sensitive, is lengthy and requires 48-72 h to assess STEC presence in a sample. In this study, we investigated if Vero cells in a three-dimensional (3D) platform would provide improved sensitivity for rapid screening of STEC. Vero cells (epithelial kidney cell line) were grown as a monolayer (2D) or in a collagen-matrix (3D) and exposed to Shiga-toxin (Stx) preparation or STEC cells that were pre-exposed to antibiotics (mitomycin C, ciprofloxacin, or polymyxin B) for toxin induction. Lactate dehydrogenase (LDH) release from Vero cells was used as a biomarker for cytotoxicity. Modified tryptic soy broth (mTSB) as enrichment broth containing mitomycin C (2 μg/ml) or ciprofloxacin (100 ng/ml) significantly induced Stx production, which was further confirmed by the dot-immunoblot assay. The 3D Vero platform detected STEC after 6 h post-infection with cytotoxicity values ranging from 33 to 79%, which is considerably faster than the traditional 2D platform, when tested with STEC. The cytotoxicity for non-Stx producing bacteria, Salmonella, Listeria, Citrobacter, Serratia, and Hafnia was found to be below the cytotoxicity cutoff value of 15%. The detection limit for the 3D Vero cell assay was estimated to be 107 CFU/ml for bacteria and about 32 ng/ml for Stx in 6 h. STEC-inoculated ground beef samples (n = 27) resulted in 38-46% cytotoxicity, and the bacterial isolates (n = 42) from ground beef samples were further confirmed to be stx1 and stx2 positive in a multiplex PCR yielding a very low false-positive result. This 3D cell-based screening assay relies on mammalian cell pathogen interaction that can complement other molecular techniques for the detection of cell-free Stx or STEC cells from food samples for early detection and prevention.

Simultaneous detection of Salmonella enterica, Escherichia coli and Listeria monocytogenes in food using a light scattering sensor

AIM

To investigate the use of a light scattering sensor, BActerial Rapid Detection using Optical scattering Technology (BARDOT) coupled with a multipathogen selective medium, Salmonella, Escherichia and Listeria (SEL), for concurrent detection of the three major foodborne pathogens in a single assay.

METHODS AND RESULTS

BARDOT was used to detect and distinguish the three major pathogens, Salmonella enterica, Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes from food based on colony scatter signature patterns on SEL agar (SELA). Multiple strains of three test pathogens were grown on SELA, and BARDOT was used to generate colony scatter image libraries for inclusive (SEL Library) and exclusive (non-SEL Library) bacterial group. These pathogens were further differentiated using the SEL scatter image library. Raw chicken and hotdog samples were artificially inoculated with pathogens (100 CFU per 25 g each), and enriched in SEL broth at 37°C for 18 h and colonies were grown on SELA for 11-22 h before screening with BARDOT. The BARDOT sensor successfully detected and differentiated Salmonella, STEC and Listeria on SELA with high classification accuracy 92-98%, 91-98% and 83-98% positive predictive values (PPV) respectively; whereas the nontarget strains showed only 0-13% PPV. BARDOT-identified colonies were further confirmed by multiplex PCR targeting inlB gene of L. monocytogenes, stx2 of STEC and sefA of S. enterica serovar Enteritidis.

CONCLUSIONS

The results show that BARDOT coupled with SELA can efficiently screen for the presence of three major pathogens simultaneously in a test sample within 29-40 h.

SIGNIFICANCE AND IMPACT OF THE STUDY

This innovative SELA-BARDOT detection platform can reduce turnaround time and economic burden on food industries by offering a label-free, noninvasive on-plate multipathogen screening technology for reducing microbial food safety and public health concerns.

Electrochemiluminescent detection of Escherichia coli O157:H7 based on Ru(bpy)3 2+/ZnO nanorod arrays

Foodborne pathogens are perpetual threats to human and animal health. Detection of pathogens requires accurate, sensitive, rapid and point-of-care diagnostic assays. In this study, we described a simple and sensitive electrochemiluminescent (ECL) assay to detect the deadly bacteria Escherichia coli O157:H7 by [Formula: see text]-coated ZnO nanorods arrays (NAs). The [Formula: see text]-coated ZnO NAs were fabricated by immobilizing [Formula: see text] on ZnO NAs with a large specific surface area and good conductivity. An [Formula: see text]-2-(dibutylamino)-ethanol (DBAE) system coated on ZnO NAs exhibits high ECL intensity, rapid response and good stability. This system was further developed as an ECL immunosensor used in the detection of E. coli O157:H7. The proposed ECL immunosensor exhibits a broad detection range within the scope of 200-100 000 CFU ml^-1 and quite a low detection limit of 143 CFU ml^-1. The high specificity, remarkable reproducibility and good stability offer a sensitive, selective, and convenient pathway for detecting E. coli O157:H7 in the field of food safety and clinical diagnosis.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Impedimetric detection of bacteria by using a microfluidic chip and silver nanoparticle based signal enhancement

The authors describe a method that can significantly improve the performance of impedimetric detection of bacteria. A multifunctional microfluidic chip was designed consisting of interdigitated microelectrodes and a micro-mixing zone with a Tesla structure. This maximizes the coating of bacterial surfaces with nanoparticles and results in improved impedimetric detection. The method was applied to the detection of Escherichia coli O157:H7 (E. coli). Silver enhancement was accomplished by coating E.coli with the cationic polymer diallyldimethylammonium chloride (PDDA) to form positively charged E. coli/PDDA complexes. Then, gold nanoparticles (AuNPs) were added, and the resulting E. coli/PDDA/AuNPs complexes were collected at interdigitated electrodes via positive dielectrophoresis (pDEP). A silver adduct was then formed on the E. coli/PDDA/AuNP complexes by using silver enhancement solutions and by using the AuNPs as catalysts. The combination of pDEP based capture and of using silver adducts reduces impedance by increasing the conductivity of the solution and the double layer capacitance around the microelectrodes. Impedance decreases linearly in the 2 × 10³-2 × 10⁵ cfu·mL^-1 E. coli concentration range, with a 500 cfu·mL^-1 detection limit. Egg shell wash samples and tap water spiked with E. coli were successfully used for validation, and this demonstrates the practical application of this method. Graphical abstract Schematic representation of the AuNP@Ag enhancement method integrated with multifunctional microfluidic chip platform for impedimetric quantitation of bacteria. The method significantly improves the performance of impedimetric detection of bacteria.

Beta-Hemolytic Bacteria Selectively Trigger Liposome Lysis, Enabling Rapid and Accurate Pathogen Detection

For more than a century, blood agar plates have been the only test for beta-hemolysis. Although blood agar cultures are highly predictive for bacterial pathogens, they are too slow to yield actionable information. Here, we show that beta-hemolytic pathogens are able to lyse and release fluorophores encapsulated in sterically stabilized liposomes whereas alpha and gamma-hemolytic bacteria have no effect. By analyzing fluorescence kinetics, beta-hemolytic colonies cultured on agar could be distinguished in real time with 100% accuracy within 6 h. Additionally, end point analysis based on fluorescence intensity and machine-extracted textural features could discriminate between beta-hemolytic and cocultured control colonies with 99% accuracy. In broth cultures, beta-hemolytic bacteria were detectable in under an hour while control bacteria remained negative even the next day. This strategy, called beta-hemolysis triggered-release assay (BETA) has the potential to enable the same-day detection of beta-hemolysis with single-cell sensitivity and high accuracy.

The Use of Electrochemical Biosensors in Food Analysis

Rapid and accurate analysis of food produce is essential to screen for species that may cause significant health risks like bacteria, pesticides and other toxins. Considerable developments in analytical techniques and instrumentation, for example chromatography, have enabled the analyses and quantitation of these contaminants. However, these traditional technologies are constrained by high cost, delayed analysis times, expensive and laborious sample preparation stages and the need for highly-trained personnel. Therefore, emerging, alternative technologies, for example biosensors may provide viable alternatives. Rapid advances in electrochemical biosensors have enabled significant gains in quantitative detection and screening and show incredible potential as a means of countering such limitations. Apart from demonstrating high specificity towards the analyte, these biosensors also address the challenge of the multifactorial food industry of providing high analytical accuracy amidst complex food matrices, while also overcoming differing densities, pH and temperatures. This (public and Industry) demand for faster, reliable and cost-efficient analysis of food samples, has driven investment into biosensor design. Here, we discuss some of the recent work in this area and critique the role and contributions biosensors play in the food industry. We also appraise the challenges we believe biosensors need to overcome to become the industry standard.

Current Technical Approaches for the Early Detection of Foodborne Pathogens: Challenges and Opportunities

The development of novel and high-tech solutions for rapid, accurate, and non-laborious microbial detection methods is imperative to improve the global food supply. Such solutions have begun to address the need for microbial detection that is faster and more sensitive than existing methodologies (e.g., classic culture enrichment methods). Multiple reviews report the technical functions and structures of conventional microbial detection tools. These tools, used to detect pathogens in food and food homogenates, were designed via qualitative analysis methods. The inherent disadvantage of these analytical methods is the necessity for specimen preparation, which is a time-consuming process. While some literature describes the challenges and opportunities to overcome the technical issues related to food industry legal guidelines, there is a lack of reviews of the current trials to overcome technological limitations related to sample preparation and microbial detection via nano and micro technologies. In this review, we primarily explore current analytical technologies, including metallic and magnetic nanomaterials, optics, electrochemistry, and spectroscopy. These techniques rely on the early detection of pathogens via enhanced analytical sensitivity and specificity. In order to introduce the potential combination and comparative analysis of various advanced methods, we also reference a novel sample preparation protocol that uses microbial concentration and recovery technologies. This technology has the potential to expedite the pre-enrichment step that precedes the detection process.

Point-of-care test for cervical cancer in LMICs

Cervical cancer screening using Papanicolaou's smear test has been highly effective in reducing death from this disease. However, this test is unaffordable in low- and middle-income countries, and its complexity has limited wide-scale uptake. Alternative tests, such as visual inspection with acetic acid or Lugol's iodine and human papillomavirus DNA, are sub-optimal in terms of specificity and sensitivity, thus sensitive and affordable tests with high specificity for on-site reporting are needed. Using proteomics and bioinformatics, we have identified valosin-containing protein (VCP) as differentially expressed between normal specimens and those with cervical intra-epithelial neoplasia grade 2/3 (CIN2/CIN3+) or worse. VCP-specific immunohistochemical staining (validated by a point-of-care technology) provided sensitive (93%) and specific (88%) identification of CIN2/CIN3+ and may serve as a critical biomarker for cervical-cancer screening. Future efforts will focus on further refinements to enhance analytic sensitivity and specificity of our proposed test, as well as on prototype development.

3D-printed microfluidic magnetic preconcentrator for the detection of bacterial pathogen using an ATP luminometer and antibody-conjugated magnetic nanoparticles

Various types of microfluidic systems have been developed to detect bacterial pathogens. However, most of these require enrichment steps that take at least several hours when detecting bacteria that are present with a low number of cells and, in addition, fabrication requires complicated assembly steps. In this study, we report the development of 3D microfluidic magnetic preconcentrator (3DμFMP) made of plastic via 3D printing without the need for any assembly. 3DμFMP could selectively preconcentrate enterohemorrhagic Escherichia coli O157:H7 in 100mL by a factor of 700 within 1h using antibody-conjugated magnetic nanoparticles (Ab-MNPs). With the combined use of an ATP luminometer, as low as 10 E. coli O157:H7 CFU (colony forming unit)/mL could be detected in blood. These results demonstrate the feasibility of 3DμFMP as a preconcentrator to improve the detection limit of existing bacterial detection systems.

Plant Molecular Farming: Much More than Medicines

Plants have emerged as commercially relevant production systems for pharmaceutical and nonpharmaceutical products. Currently, the commercially available nonpharmaceutical products outnumber the medical products of plant molecular farming, reflecting the shorter development times and lower regulatory burden of the former. Nonpharmaceutical products benefit more from the low costs and greater scalability of plant production systems without incurring the high costs associated with downstream processing and purification of pharmaceuticals. In this review, we explore the areas where plant-based manufacturing can make the greatest impact, focusing on commercialized products such as antibodies, enzymes, and growth factors that are used as research-grade or diagnostic reagents, cosmetic ingredients, and biosensors or biocatalysts. An outlook is provided on high-volume, low-margin proteins such as industrial enzymes that can be applied as crude extracts or unprocessed plant tissues in the feed, biofuel, and papermaking industries.

Recent Advancements in Nanobioassays and Nanobiosensors for Foodborne Pathogenic Bacteria Detection

Bacterial pathogens are one of the leading causes of food safety incidents and product recalls worldwide. Timely detection and identification of microbial contamination in agricultural and food products is crucial for disease prevention and outbreak investigation. In efforts to improve and/or replace time-consuming and laborious "gold standards" for pathogen detection, numerous alternative rapid methods have been proposed in the past 15 years, with a trend toward incorporating nanotechnology and nanomaterials in food pathogen detection. This article is a review of the use of nanotechnology in various detection and sample preparation techniques and advancements in nanotechnology applications in food matrices. Some practical considerations in nanobioassay design are discussed, and the gaps between research status quo and market demands are identified.

Recent and emerging innovations in Salmonella detection: a food and environmental perspective

Salmonella is a diverse genus of Gram‐negative bacilli and a major foodborne pathogen responsible for more than a million illnesses annually in the United States alone. Rapid, reliable detection and identification of this pathogen in food and environmental sources is key to safeguarding the food supply. Traditional microbiological culture techniques have been the ‘gold standard’ for State and Federal regulators. Unfortunately, the time to result is too long to effectively monitor foodstuffs, especially those with very short shelf lives. Advances in traditional microbiology and molecular biology over the past 25 years have greatly improved the speed at which this pathogen is detected. Nonetheless, food and environmental samples possess a distinctive set of challenges for these newer, more rapid methodologies. Furthermore, more detailed identification and subtyping strategies still rely heavily on the availability of a pure isolate. However, major shifts in DNA sequencing technologies are meeting this challenge by advancing the detection, identification and subtyping of Salmonella towards a culture‐independent diagnostic framework. This review will focus on current approaches and state‐of‐the‐art next‐generation advances in the detection, identification and subtyping of Salmonella from food and environmental sources.

On-chip electrical detection of parallel loop-mediated isothermal amplification with DG-BioFETs for the detection of foodborne bacterial pathogens

Over one million DG-BioFETs are used for the parallel electrical detection of LAMP reactions identifying the presence of bacterial pathogens, demonstrating a miniaturized DNA-based screening platform.

Microfluidics using a thiol-acrylate resin for fluorescence-based pathogen detection assays

We demonstrate thiol-acrylate microfluidics prepared via soft lithography for single-step protein immobilization and fluorescence-based pathogen detection. Such microfluidics are formed via room temperature curing, and bonded without oxygen plasma. The background fluorescence of the resin was found to be similar to PDMS for several filter sets. We also show that thiol-acrylate devices are able to bond to gold-coated surfaces, which allows for integration with microfabricated sensors.

Responsive Food Packaging: Recent Progress and Technological Prospects

Responsive food packaging is an emerging field in food packaging research and the food industry. Unlike active packaging, responsive packaging systems react to stimuli in the food or the environment to enable real time food quality and food safety monitoring or remediation. This review attempts to define and clarify the different classes of food packaging technologies. Special emphasis is given to the description of responsive food packaging including its technical requirements, the state of the art in research and the current expanding market. The development and promises of stimuli responsive materials in responsive food packaging are addressed, along with current challenges and future directions to help translate research developments into commercial products.

Single-Digit Pathogen and Attomolar Detection with the Naked Eye Using Liposome-Amplified Plasmonic Immunoassay

We introduce an enzyme-free plasmonic immunoassay with a binary (all-or-none) response. The presence of a single pathogen in the sample results in a chemical cascade reaction leading to a large red to dark-blue colorimetric shift visible to the naked eye. The immediate and amplified response is initiated by a triggered breakdown of cysteine-loaded nanoliposomes and subsequent aggregation of plasmonic gold nanoparticles. Our approach enabled visual detection of a single-digit live pathogen of Salmonella, Listeria, and E. coli O157 in water and food samples. Furthermore, the assay allowed a naked-eye detection of target antibody concentrations as low as 6.7 attomolar (600 molecules in 150 μL); six orders of magnitude lower than conventional enzyme-linked immunosorbent assay (ELISA).

Membrane filter-assisted surface enhanced Raman spectroscopy for the rapid detection of E. coli O157:H7 in ground beef

Consumption of food contaminated with Escherichia coli O157:H7 is one of the major concerns in ensuring food safety. Techniques that are simple and suitable for fast screening to detect and identify pathogens in the food chain is vital to ensure food safety. In this work, we propose a simple and rapid technique to detect low levels of E. coli O157:H7 using membrane filtration and silver intensification steps in combination with surface enhanced Raman spectroscopy (SERS) analysis. The target bacteria can be captured and separated efficiently by two different antibody bearing nanoparticle complexes (magnetic nanoparticles and gold nanoparticles with a Raman reporter). After centrifugal filtration, the bacteria-nanoparticle complexes left on the filter membrane were localized by silver intensification process before probing by SERS. Extremely low concentration of E. coli O157:H7 (~10 CFU/mL) could be detected within 1h and 3h from both pure culture and ground beef samples, respectively. This method can potentially be used as an effective pathogen screening tool for routine monitoring.