Novel detection of Escherichia coli beta-D-glucuronidase activity using a microbially-modified glassy carbon electrode and its potential for faecal pollution monitoring

Progress in methods for the detection of viable Escherichia coli

Escherichia coli (E. coli) is a prevalent enteric bacterium and a necessary organism to monitor for food safety and environmental purposes. Developing efficient and specific methods is critical for detecting and monitoring viable E. coli due to its high prevalence. Conventional culture methods are often laborious and time-consuming, and they offer limited capability in detecting potentially harmful viable but non-culturable E. coli in the tested sample, which highlights the need for improved approaches. Hence, there is a growing demand for accurate and sensitive methods to determine the presence of viable E. coli. This paper scrutinizes various methods for detecting viable E. coli, including culture-based methods, molecular methods that target DNAs and RNAs, bacteriophage-based methods, biosensors, and other emerging technologies. The review serves as a guide for researchers seeking additional methodological options and aiding in the development of rapid and precise assays. Moving forward, it is anticipated that methods for detecting E. coli will become more stable and robust, ultimately contributing significantly to the improvement of food safety and public health.

The role of gut microbial β-glucuronidase in drug disposition and development

Gut microbial β-glucuronidase (gmGUS) is involved in the disposition of many endogenous and exogenous compounds. Preclinical studies have shown that inhibiting gmGUS activity affects drug disposition, resulting in reduced toxicity in the gastrointestinal tract (GIT) and enhanced systemic efficacy. Additionally, manipulating gmGUS activity is expected to be effective in preventing/treating local or systemic diseases. Although results from animal studies are promising, challenges remain in developing drugs by targeting gmGUS. Here, we review the role of gmGUS in host health under physiological and pathological conditions, the impact of gmGUS on the disposition of phenolic compounds, models used to study gmGUS activity, and the perspectives and challenges in developing drugs by targeting gmGUS.

Rapid electrochemical detection of Escherichia coli using nickel oxidation reaction on a rotating disk electrode

A standalone electrochemical method for detecting the bacterium Escherichia coli in water was developed using a nickel electrode and no biorecognition element. Electric current responses from different E. coli concentrations were recorded based on their interaction with a locally formed electrocatalyst. A rotating disk electrode was used to minimize the mass transport limitations at the interface. Results from experiments with the rotating disk electrode also paved the way for hypothesizing the detection mechanism. The operating conditions were established for sensing the electric current responses in the presence of E. coli. The least-squares linear regression model was fit to the data obtained from currents of some known E. coli concentrations. This probe had a detection limit in the order of 104 CFU/ml. The response time to detect the presence/absence of E. coli was less than half a second, while the total assay time, including quantification of its concentration, was 10 min. The electric current response from a solution mixed with E. coli and S. aureus showed current similar to E. coli only solution indicating the specificity of the sensor to respond to signals from E. coli. This electrochemical microbial sensor's uniqueness lies in its ability to rapidly detect E. coli by forming the catalyst locally on demand without the attachment of biorecognition elements.

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.

Bluephage: A rapid method for the detection of somatic coliphages used as indicators of fecal pollution in water

The use of somatic coliphages as indicators of fecal and viral pollution in water and food has great potential due to the reliability, reproducibility, speed and cost effectiveness of methods for their detection. Indeed, several countries already use this approach in their water management policies. Although standardized protocols for somatic coliphage detection are available, user-friendly commercial kits would facilitate their routine implementation in laboratories. The new method presented here allows detection of up to 1 somatic coliphage in under 3.5 h, well within one working day. The method is based on a modified Escherichia coli strain with knocked-out uidB and uidC genes, which encode the transport of glucuronic acid inside cells, and overexpressing uidA, which encodes the enzyme β-glucuronidase. The enzyme accumulated in the bacterial cells only has contact with its substrate after cell lysis, such as that caused by phages, since the strain cannot internalize the substrate. When the enzyme is released into the medium, which contains a chromogen analogous to glucuronic acid, it produces a change of color from yellow to dark blue. This microbiological method for the determination of fecal pollution via the detection of culturable microorganisms can be applied to diverse sample types and volumes for qualitative (presence/absence) and quantitative analysis and is the fastest reported to date.

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.

Developing Biosensors in Developing Countries: South Africa as a Case Study

A mini-review of the reported biosensor research occurring in South Africa evidences a strong emphasis on electrochemical sensor research, guided by the opportunities this transduction platform holds for low-cost and robust sensing of numerous targets. Many of the reported publications centre on fundamental research into the signal transduction method, using model biorecognition elements, in line with international trends. Other research in this field is spread across several areas including: the application of nanotechnology; the identification and validation of biomarkers; development and testing of biorecognition agents (antibodies and aptamers) and design of electro-catalysts, most notably metallophthalocyanine. Biosensor targets commonly featured were pesticides and metals. Areas  of regional import to sub-Saharan Africa, such as HIV/AIDs and tuberculosis diagnosis, are also apparent in a review of the available literature. Irrespective of the targets, the challenge to the effective deployment of such sensors remains shaped by social and economic realities such that the requirements thereof are for low-cost and universally easy to operate devices for field settings. While it is difficult to disentangle the intertwined roles of national policy, grant funding availability and, certainly, of global trends in shaping areas of emphasis in research, most notable is the strong role that nanotechnology, and to a certain extent biotechnology, plays in research regarding biosensor construction. Stronger emphasis on collaboration between scientists in theoretical modelling, nanomaterials application and or relevant stakeholders in the specific field (e.g., food or health monitoring) and researchers in biosensor design may help evolve focused research efforts towards development and deployment of low-cost biosensors.

Gold nanoparticle decorated graphene sheet-polypyrrole based nanocomposite: its synthesis, characterization and genosensing application

We report herein the synthesis of gold nanoparticle (GNP) decorated-graphene sheets (GO-GNPs) using the template of graphene oxide (GO) by a one-pot solution-based method. A polypyrrole-GO decorated GNP nanocomposite (GO-GNP/PPY) has been electropolymerized using a potentiodynamic method on an indium tin oxide (ITO) coated glass substrate. The as-synthesized nanocomposites are characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopy. It has been found that GNPs of ca. 13 nm are uniformly dispersed on the surface of GO, and have a high electrochemically active surface area. The surface morphology studies show that PPY structure changes from nanoflowers to nanostars and then to nanosheets with an increase in the scan rate (20-200 mV s(-1)). The prepared GO-GNP/PPY/ITO electrode was further used as a genosensor, where the electrochemical response was measured using methylene blue (MB) as a redox indicator. The genosensor shows a response time of 60 s with high sensitivity (1 × 10(-15) M) and linearity (1 × 10(-15)-1 × 10(-6) M) with the correlation coefficient of 0.9975.

Rapid amperometric detection of Escherichia coli in wastewater by measuring β-D glucuronidase activity with disposable carbon sensors

An assay on the indirect amperometric quantification of the β-D-Glucuronidase (GLUase) activity was developed for the rapid and specific detection of Escherichia coli (E. coli) in complex environmental samples. The p-aminophenyl β-D-glucopyranoside (PAPG) was selected as an electrochemical substrate for GLUase measurement and the p-aminophenol (PAP) released during the enzymatic hydrolysis was monitored by cyclic voltammetry with disposable carbon screen-printed sensors. The intensity of the measured anodic peak current was proportional to the amount of GLUase, and therefore to the number of E. coli in the tested sample. Once the substrate concentration and pH values optimized, a GLUase detection limit of 10 ng mL(-1) was achieved. Using a procedure involving a filtration step of the bacteria followed by their incubation with the substrate solution containing both the nonionic detergent Triton X-100 as permeabilization agent and the culture media Luria broth to monitor the growth, filtered bacterial cells ranging from 5 × 10(4) to 10(8) UFC/membrane were detected within 3 h. The amperometric assay was applied to the determination of fecal contamination in raw and treated wastewater samples and it was successfully compared with conventional bacterial plating methods and uidA gene quantitative PCR. Owing to its ability to perform measurements in turbid media, the GLUase amperometric method is a reliable tool for the rapid and decentralized quantification of viable but also nonculturable E. coli in complex environmental samples.

Current Perspectives on Viable but Non-Culturable (VBNC) Pathogenic Bacteria

Under stress conditions, many species of bacteria enter into starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. Several human pathogenic bacteria have been reported to enter into the VBNC state under these conditions. The pathogenic VBNC bacteria cannot be grown using conventional culture media, although they continue to retain their viability and express their virulence. Though there have been debates on the VBNC concept in the past, several molecular studies have shown that not only can the VBNC state be induced under in vitro conditions but also that resuscitation from this state is possible under appropriate conditions. The most notable advance in resuscitating VBNC bacteria is the discovery of resuscitation-promoting factor (Rpf), which is a bacterial cytokines found in both Gram-positive and Gram-negative organisms. VBNC state is a survival strategy adopted by the bacteria, which has important implication in several fields, including environmental monitoring, food technology, and infectious disease management; and hence it is important to investigate the association of bacterial pathogens under VBNC state and the water/foodborne outbreaks. In this review, we describe various aspects of VBNC bacteria, which include their proteomic and genetic profiles under the VBNC state, conditions of resuscitation, methods of detection, antibiotic resistance, and observations on Rpf.

Fast detection and quantification of Escherichia coli using the base principle of the microbial fuel cell

Escherichia coli is an important microbial indicator of fecal contamination, making accurate quantitative detection of E. coli a key to ensuring public health. In this study, a microbial fuel cell (MFC) was used as a detection unit of an E. coli sensor, and specific enzymes expressed in E. coli, such as β-D-galactosidase (GAL) and β-D-glucuronidase (GUS), were exploited as biological detection elements. As substrates, 4-aminophenyl-β-D-galactopyranoside (4-APGal) were used for GAL detection, whereas 8-hydroxyquinoline glucuronide (8-HQG) and 4-nitrophenyl β-D-glucuronide (PNPG) were used for GUS detection. Once these substrates were hydrolyzed by GAL or GUS, they became electrochemically active products, which were, in turn, oxidized on the anode of the MFC reactor. The power output of the MFC reactor increased sharply when E. coli in the reactor reached the critical concentration. Accordingly, the time required to reach the highest voltage output was recorded as a detection time (DT), and a negative linear relationship was established between DT and the logarithm of the initial concentration of E. coli in the samples studied. The DTs of laboratory samples were 140 min and 560 min for initial concentrations of 1.9 × 10(7) CFU/mL and 42 CFU/mL at 44.5 °C. Moreover, the DTs for GUS assays were further shortened by induction with methyl β-D-glucuronide sodium salt (MetGlu). The quantitative relationship between DTs and initial E. coli concentrations established from replicate laboratory sample assays allowed estimation of the E. coli concentration in environmental samples, but with approximately 100 min of lag time. The lag time was also observed with E. coli samples that were prepared by starving cells in a laboratory.

Application of rapid enzyme assay techniques for monitoring of microbial water quality

Rapid enzyme assay techniques based on direct measurement of beta-d-galactosidase (GALase) or beta-d-glucuronidase (GLUase) activity without selective cultivation are used for rapid estimation of the level of coliform bacteria and Escherichia coli in water samples. Reported detection limits using fluorogenic substrates correspond to culturable target bacteria concentrations that can be appropriate within present guidelines for recreational waters. The rapidity, that is detection within one hour, compromises the specificity of the assay; enzyme activity contributions from other than target bacteria need to be considered, particularly at low levels of target bacteria. Enzyme activities are more persistent than the culturability of target bacteria to environmental and disinfection stress, thus water samples may express enzyme activities of both culturable and viable non-culturable cells.