Development and application of hydrogels in pathogenic bacteria detection in foods

Hydrogels are 3D networks of water-swollen hydrophilic polymers. It possesses unique properties (e.g., carrying biorecognition elements and creating a micro-environment) that make it highly suitable for bacteria detection (e.g., expedited and effective bacteria detection) and mitigation of bacterial contamination in specific environments (e.g., food systems). This study first introduces the materials used to create hydrogels for bacteria detection and the mechanisms for detection. We also summarize different hydrogel-based detection methods that rely on external stimuli and biorecognition elements, such as enzymes, temperature, pH, antibodies, and oligonucleotides. Subsequently, a range of widely utilized bacterial detection technologies were discussed where recently hydrogels are being used. These modifications allow for precise, real-time diagnostics across varied food matrices, responding effectively to industry needs for sensitivity, scalability, and portability. After highlighting the utilization of hydrogels and their role in these detection techniques, we outline limitations and advancements in the methods for the detection of foodborne pathogenic bacteria, especially the potential application of hydrogels in the food industry.

Development of nanocellulose hydrogels for application in the food and biomedical industries: A review

As the most abundant and renewable natural resource, cellulose has attracted significant attention and research interest for the production of hydrogels (HGs). To address environmental issues and emerging demands, the benefits of naturally produced HGs include excellent mechanical properties and superior biocompatibility. HGs are three-dimensional networks created by chemical or physical cross-linking of linear or branched hydrophilic polymers and have high capacity for absorption of water and biological fluids. Although widely used in the food and biomedical fields, most HGs are not biodegradable. Nanocellulose hydrogels (NC-HGs) have been extensively applied in the food industry for detection of freshness, chemical additives, and substitutes, as well as the biomedical field for use as bioengineering scaffolds and drug delivery systems owing to structural interchangeability and stimuli-responsive properties. In this review article, the sources, structures, and preparation methods of NC-HGs are described, applications in the food and biomedical industries are summarized, and current limitations and future trends are discussed.

Digital metabolic activity assay enables fast assessment of 2D materials bactericidal efficiency

BACKGROUND

The identification and quantification of viable Escherichia coli (E. coli) are important in multiple fields including the development of antimicrobial materials, water quality, food safety and infections diagnosis. However, the standard culture-based methods of viable E. coli detection suffer from long detection times (24 h) and complex operation, leaving the unmet requirement for fast assessing the efficiency of antimicrobial materials, early alerting the contamination of water and food, and immediately treatment of infections.

RESULTS

We present a digital β-d-glucuronidase (GUS) assay in a self-priming polydimethylsiloxane (PDMS) microfluidic chip for rapid E. coli identification and quantification. The GUS expression in viable bacteria was investigated to develop a fast GUS assay at the single-cell level. Single E. coli were stochastically discretized in picoliter chambers and identified by specific GUS activity. The digital GUS assay enabled identifying E. coli within 3 h and quantifying within 4 h for different E. coli subtypes. The specificity of our method was confirmed by using blended bacteria including E. coli, Bacillus, Shigella and Vibrio. We utilized digital GUS assay to enumerate viable E. coli after incubated with antibacterial materials for assessing the antibacterial efficiency. Moreover, the degassed chip can realize automatic sample distribution without external instruments.

SIGNIFICANCE

The results demonstrated the functionality and practicability of digital GUS assay for single E. coli identification and quantification. With air-tight packaging, the developed chip has the potential for on-site E. coli analysis and could be deployed for diagnosis of E. coli infections, antimicrobial susceptibility testing, and warning the fecal pollution of water. Digital GUS assay provides a paradigm, examining the activity of metabolic enzyme, for detecting the viable bacteria other than E. coli.

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

Recent Advances in Optical Sensing for the Detection of Microbial Contaminants

Microbial contaminants are responsible for several infectious diseases, and they have been introduced as important potential food- and water-borne risk factors. They become a global burden due to their health and safety threats. In addition, their tendency to undergo mutations that result in antimicrobial resistance makes them difficult to treat. In this respect, rapid and reliable detection of microbial contaminants carries great significance, and this research area is explored as a rich subject within a dynamic state. Optical sensing serving as analytical devices enables simple usage, low-cost, rapid, and sensitive detection with the advantage of their miniaturization. From the point of view of microbial contaminants, on-site detection plays a crucial role, and portable, easy-applicable, and effective point-of-care (POC) devices offer high specificity and sensitivity. They serve as advanced on-site detection tools and are pioneers in next-generation sensing platforms. In this review, recent trends and advances in optical sensing to detect microbial contaminants were mainly discussed. The most innovative and popular optical sensing approaches were highlighted, and different optical sensing methodologies were explained by emphasizing their advantages and limitations. Consequently, the challenges and future perspectives were considered.

Multifunctional nanofibrous mats: toward antibacterial and anti-inflammatory applications, and visual bacterial diagnosis

In most circumstances, wounds face the challenges of bacterial invasions and inappropriate inflammatory responses when they lack proper wound management. Endowing dressings with both antibacterial and anti-inflammatory functions is a compelling strategy for resolving the above issues. However, seizing the right moment to change the dressings and providing satisfactory management of wounds are still urgently required. Herein, an antibacterial and anti-inflammatory nanofibrous mat is proposed by encapsulating antibiotic gentamicin sulfate (GS) and anti-inflammatory drug ibuprofen (IB) into nanofibers via a coaxial electrospinning technique and is further decorated with Prussian blue nanocrystals (PBNCs) to enhance anti-inflammatory activity and, more importantly, to monitor bacterial infections and guide dressing changes in a timely manner. Such a nanofibrous mat releases most of the therapeutic drugs within 120 min and reveals excellent antibacterial activity and anti-inflammatory ability. Specifically, it can destroy both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), as well as conspicuously reduce the production of reactive oxygen species (ROS) and the expression of pro-inflammatory cytokines in macrophages. In addition, the nanofibrous mat can be used for point-of-use diagnosis of living bacteria relying on the naked eye or color analysis, which exhibits the potential of monitoring wound infection and guiding dressing changes promptly. This finding demonstrates the theranostic applications of multifunctional nanofibrous mats in wound healing.

A review on urinary tract infections diagnostic methods: Laboratory-based and point-of-care approaches

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide. This type of infections can be healthcare-associated or community-acquired and affects millions of people every year. Different diagnostic procedures are available to detect pathogens in urine and they can be divided into two main categories: laboratory-based and point-of-care (POC) detection techniques. Traditional methodologies are often time-consuming, thus, achieving a rapid and accurate identification of pathogens is a challenging feature that has been pursued by many research groups and companies operating in this area. The purpose of this review is to compare and highlight advantages and disadvantages of the traditional and currently most used detection methods, as well as the emerging POC approaches and the relevant advances in on-site detection of pathogens´ mechanisms, suitable to be adapted to UTI diagnosis. Lately, the commercially available UTI self-testing kits and devices are helping in the diagnosis of urinary infections as patients or care givers are able to perform the test, easily and comfortably at home and, upon the result, decide when to attend an appointment/Urgent Health Care Unit.

The β-galactosidase assay in perspective: Critical thoughts for biosensor development

Recently, the β-galactosidase assay has become a key component in the development of assays and biosensors for the detection of enterobacteria and E. coli in water quality monitoring. The assay has often performed below its maximum potential, mainly due to a poor choice of conditions. In this study we establish a set of optimal conditions and provide a rough estimate of how departure from optimal values reduces the output of the assay potentially decreasing its sensitivity. We have established that maximum response for detecting low cell concentrations requires an induction of the samples using IPTG at a concentration of 0.2 mM during 180 min. Permeabilization of the samples is mandatory as lack of it results in an almost 60% reduction in assay output. The choice of enzyme substrate is critical as different substrates yield products with different extinction coefficients or fluorescence yields. The concentration of substrate used must be high enough (around 3 to 4 times K_m) to ensure that the activity measured is not substrate limited. Finally, as the color/fluorescence of the reaction products is highly dependent on pH, care must be taken to ensure that pH at the time of reading is high enough to provide maximum signal.

Evaluation of ligand modified poly (N-Isopropyl acrylamide) hydrogel for etiological diagnosis of corneal infection

Corneal ulcers, a leading cause of blindness in the developing world are treated inappropriately without prior microbiology assessment because of issues related to availability or cost of accessing these services.

In this work we aimed to develop a device for identifying the presence of Gram-positive or Gram-negative bacteria or fungi that can be used by someone without the need for a microbiology laboratory. Working with branched poly (N-isopropyl acrylamide) (PNIPAM) tagged with Vancomycin, Polymyxin B, or Amphotericin B to bind Gram-positive bacteria, Gram-negative bacteria and fungi respectively, grafted onto a single hydrogel we demonstrated specific binding of the organisms. The limit of detection of the microbes by these polymers was between 10 and 4 organisms per high power field (100X) for bacteria and fungi binding polymers respectively. Using ex vivo and animal cornea infection models infected with bacteria, fungi or both we than demonstrated that the triple functionalised hydrogel could pick up all 3 organisms after being in place for 30 min. To confirm the presence of bacteria and fungi we used conventional microbiology techniques and fluorescently labelled ligands or dyes.

While we need to develop an easy-to-use either a colorimetric or an imaging system to detect the fluorescent signals, this study presents for the first time a simple to use hydrogel system, which can be applied to infected eyes and specifically binds different classes of infecting agents within a short space of time. Ultimately this diagnostic system will not require trained microbiologists for its use and will be used at the point-of-care.

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Functionalised branched Poly N-isopropyl acrylamide binds corneal ulcer causing microorganisms.

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The functionalised polymers demonstrated specific binding to gram positive, gram negative and fungi.

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Grafting three different polymers on a single hydrogel retained this specific binding for microorganisms.

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Triple functionalised hydrogels were effective in picking up microorganisms in ex-vivo and animal cornea infection models.

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Application for a duration of 30 min was sufficient to pick up enough organisms for subsequent identification.

Simple and reliable enumeration of Escherichia coli concentrations in wastewater samples by measuring β-d-glucuronidase (GUS) activities via a microplate reader

Monitoring of Escherichia coli concentrations at wastewater treatment plants (WWTPs) is important to ensure process performance and protect public health. However, conventional E. coli enumeration methods are complicated and time- and labor-consuming. Here, we report a novel simple and reliable method based on β-d-glucuronidase (GUS) activity assay to enumerate E. coli concentrations in wastewater (WW) samples. An aliquot (20 μL) of the medium with fluorogenic enzyme substrate for E. coli and 180 μL of a WW sample were added to one well of a 96-well microplate. The microplate was placed in a microplate reader at 37 °C. To this end, the fluorescence intensity of a fluorogenic enzyme substrate for E. coli was measured every 10 min over 3 h to determine GUS activity. The linear increase in the fluorescence intensity representing the GUS activities showed a positive correlation with E. coli concentrations in wastewater samples. However, the correlation equations were specific to WWTPs, which could be due to the difference in the E. coli population structures among WWTPs. We observed that the wastewater matrix is not a limitation to measure the GUS activity, and a WWTP-specific correlation equation can be used as a calibration curve to estimate the E. coli concentrations in the samples collected from that site. A comparison of the results with those of culture-dependent Colilert method proved that the current method is simple and useful for the enumeration of E. coli concentrations in wastewater samples reliably.

Detection of Escherichia coli O157:H7 Using Automated Immunomagnetic Separation and Enzyme-Based Colorimetric Assay

The food industry requires rapid and simple detection methods for preventing harm from pathogenic bacteria. Until now, various technologies used to detect foodborne bacteria were time-consuming and laborious. Therefore, we have developed an automated immunomagnetic separation combined with a colorimetric assay for the rapid detection of E. coli O157:H7 in food samples. The colorimetric detection method using enzymatic reaction is fascinating because of its simplicity and rapidity and does not need sophisticated devices. Moreover, the proposed procedures for the detection of bacteria in food take less than 3 h including pre-enrichment, separation and detection steps. First, target-specific immunomagnetic beads were introduced to contaminated milk in a pre-enrichment step. Second, the pre-enriched sample solution containing target bacteria bound on immunomagnetic beads was injected into an automated pretreatment system. Subsequently, the immunomagnetic beads along with target bacteria were separated and concentrated into a recovery tube. Finally, released β-galactosidase from E. coli O157:H7 after lysis was reacted with chlorophenol red β-galactopyranoside (CPRG) used as a substrate and the colorimetric change of CPRG was determined by absorbance measuring or the naked eye. By the proposed approach in this study, we could detect 3 × 10² CFU/mL of E. coli O157:H7 from a milk sample within 3 h.

Fieldwork-based determination of design priorities for point-of-use drinking water quality sensors for use in resource-limited environments

Improved capabilities in microfluidics, electrochemistry, and portable assays have resulted in the development of a wide range of point-of-use sensors intended for environmental, medical, and agricultural applications in resource-limited environments of developing countries. However, these devices are frequently developed without direct interaction with their often-remote intended user base, creating the potential for a disconnect between users' actual needs and those perceived by sensor developers. As different analytical techniques have inherent strengths and limitations, effective measurement solution development requires determination of desired sensor attributes early in the development process. In this work, we present our findings on design priorities for point-of-use microbial water sensors based on fieldwork in rural India, as well as a guide to fieldwork methodologies for determining desired sensor attributes. We utilized group design workshops for initial identification of design priorities, and then conducted choice-based conjoint analysis interviews for quantification of user preferences among these priorities. We found the highest user preference for integrated reporting of contaminant concentration and recommended actions, as well as significant preferences for mostly reusable sensor architectures, same-day results, and combined ingredients. These findings serve as a framework for future microbial sensor development and a guide for fieldwork-based understanding of user needs.

Acute biotoxicity assessment of heavy metals in sewage sludge based on the glucose consumption of Escherichia coli

As a simple and feasible method for acute biotoxicity assessment, personal glucose meter (PGM) can be successfully applied in the early warning of environmental pollutants in sewage. In this paper, the acute biotoxicity of single and joint heavy metals in sewage and real sludge samples was systematically described based on the glucose metabolism of Escherichia coli (E. coli). Results indicated that the biotoxicity order of five single heavy metals in sewage was Hg2+ > As3+ > Cu2+ > Zn2+ > Cd2+. The joint heavy metals of Cu2+ + Zn2+, Cu2+ + Cd2+, and Cu2+ + Hg2+ produced synergistic effects, while Cu2+ + As3+ and Cd2+ + Zn2+ possessed antagonistic effects for the combined biotoxicity. In spiked sludge, Cd2+ and Zn2+ owned higher biotoxicity than Cu2+ and As3+. Notably, the electroplate factory and housing estate sludge respectively showed the highest and lowest inhibition rates as 57.4% and 17.7% under the real sludge biotoxicity assessment. These results demonstrated that PGM was a sensitive and portable method, which could be widely used for acute biotoxicity assessment of heavy metals in sewage sludge.

Novel sensor platform for rapid detection and quantification of coliforms on food contact surfaces

In this paper, a novel sensor platform based on screen printed carbon electrode coated by graphene modified polyacrylamide gel (GR/PAAGC) was developed and implemented for sampling, detection and enumeration of coliform bacteria (coliforms) on food contact surfaces. The optimized formula of polyacrylamide (PAA) and agar-agar increased the adhesive properties of the gel, being crucial for the coliforms recovery, attached to food contact surfaces. The 6-Chloro-3-indoxyl-β-D-galactopyranoside (6-CIGP) was used as a new electrochemical reporter for β-D-galactosidase activity. The released 6,6'-Dichloro-Indigo (6-DI) was directly detected by GR/PAAGC sensor. The presence of Isopropyl-β-D-thiogalactopyranoside (IPTG) and n-Octyl-β-D-thiogalactopyranoside (OBDG) in the gel contributed to reduction of the detection time. The addition of graphene enhanced the voltammetric signal and increased the conductivity of PAA gel. The anodic and cathodic peaks of the released product were directly proportional to the concentration of coliforms. Bacterial cell concentrations ranging from 1.6log₁₀CFU/mL to 6.6log₁₀CFU/mL were detected. Well-shaped, sharp voltammetric curves were generated within 3 h. Redox peaks exhibited good sensitivity with detection limits (LOD) < 0.6log₁₀CFU/mL. After series of optimization experiments, coliforms ranging from 0.6log₁₀CFU/cm² to 6.6₁₀CFU/cm² on stainless steel surfaces have been detected within 30 min with a LOD of 0.1log₁₀CFU/cm². The developed rapid, sensitive, reproducible and specific sensor successfully applied for single detection as well as for real-time monitoring of growth of coliform bacteria on stainless steel surfaces during food processing.

DipTest: A litmus test for E. coli detection in water

We have developed a new litmus paper test (DipTest) for detecting Escherichia coli (E. coli) in water samples by performing enzymatic reactions directly on the porous paper substrate. The paper strip consists of a long narrow piece of cellulose blotting paper coated with chemoattractant (at bottom edge), wax hydrophobic barrier (at the top edge), and custom formulated chemical reagents (at reaction zone immediately below the wax hydrophobic barrier). When the paper strip is dipped in water, E. coli in the water sample is attracted toward the paper strip due to a chemotaxic mechanism followed by the ascent along the paper strip toward the reaction zone due to a capillary wicking mechanism, and finally the capillary motion is arrested at the top edge of the paper strip by the hydrophobic barrier. The E. coli concentrated at the reaction zone of the paper strip will react with custom formulated chemical reagents to produce a pinkish-red color. Such a color change on the paper strip when dipped into water samples indicates the presence of E. coli contamination in potable water. The performance of the DipTest device has been checked with different known concentrations of E. coli contaminated water samples using different dip and wait times. The DipTest device has also been tested with different interfering bacteria and chemical contaminants. It has been observed that the different interfering contaminants do not have any impact on the DipTest, and it can become a potential solution for screening water samples for E. coli contamination at the point of source.

A Microfluidic Device for Rapid Screening of E. coli O157:H7 Based on IFAST and ATP Bioluminescence Assay for Water Analysis

We present a simple microfluidic system for rapid screening of Escherichia coli (E. coli) O157:H7 employing the specificity of immunomagnetic separation (IMS) via immiscible filtration assisted by surface tension (IFAST), and the sensitivity of the subsequent adenosine triphosphate (ATP) assay by the bioluminescence luciferin/luciferase reaction. The developed device was capable of detecting E. coli O157:H7 from just 6 colony forming units (CFU) in 1 mL spiked buffer within 20 min. When tested with wastewater discharged effluent samples, without pre-concentration, the device demonstrated the ability to detect 10⁴  CFU per mL seeded; suggesting great potential for point-of-need microbiological water quality monitoring.

Hydrogel Based Biosensors for In Vitro Diagnostics of Biochemicals, Proteins, and Genes

Hydrogel-based biosensors have drawn considerable attention due to their various advantages over conventional detection systems. Recent studies have shown that hydrogel biosensors can be excellent alternative systems to detect a wide range of biomolecules, including small biochemicals, pathogenic proteins, and disease specific genes. Due to the excellent physical properties of hydrogels such as the high water content and stimuli-responsive behavior of cross-linked network structures, this system can offer substantial improvement for the design of novel detection systems for various diagnostic applications. The other main advantage of hydrogels is the role of biomimetic three-dimensional (3D) matrix immobilizing enzymes and aptamers within the detection systems, which enhances their stability. This provides ideal reaction conditions for enzymes and aptamers to interact with substrates within the aqueous environment of the hydrogel. In this review, we have highlighted various novel detection approaches utilizing the outstanding properties of the hydrogel. This review summarizes the recent progress of hydrogel-based biosensors and discusses their future perspectives and clinical limitations to overcome.

A Strategy to Establish a Quality Assurance/Quality Control Plan for the Application of Biosensors for the Detection of E. coli in Water

Rapid bacterial detection using biosensors is a novel approach for microbiological testing applications. Validation of such methods is an obstacle in the adoption of new bio-sensing technologies for water testing. Therefore, establishing a quality assurance and quality control (QA/QC) plan is essential to demonstrate accuracy and reliability of the biosensor method for the detection of E. coli in drinking water samples. In this study, different reagents and assay conditions including temperatures, holding time, E. coli strains and concentrations, dissolving agents, salinity and pH effects, quality of substrates of various suppliers of 4-methylumbelliferyl glucuronide (MUG), and environmental water samples were included in the QA/QC plan and used in the assay optimization and documentation. Furthermore, the procedural QA/QC for the monitoring of drinking water samples was established to validate the performance of the biosensor platform for the detection of E. coli using a culture-based standard technique. Implementing the developed QA/QC plan, the same level of precision and accuracy was achieved using both the standard and the biosensor methods. The established procedural QA/QC for the biosensor will provide a reliable tool for a near real-time monitoring of E. coli in drinking water samples to both industry and regulatory authorities.

One-step synthesis of amikacin modified fluorescent carbon dots for the detection of Gram-negative bacteria like Escherichia coli

In this paper, we report a one-step strategy to synthesize amikacin modified fluorescent carbon dots (CDs@amikacin) for assaying pathogenic bacteria, Escherichia coli.