Protocol for the recovery and detection of Escherichia coli in environmental water samples

Sensors for Coastal and Ocean Monitoring

In situ water monitoring sensors are critical to gain an understanding of ocean biochemistry and ecosystem health. They enable the collection of high-frequency data and capture ecosystem spatial and temporal changes, which in turn facilitate long-term global predictions. They are used as decision support tools in emergency situations and for risk mitigation, pollution source tracking, and regulatory monitoring. Advanced sensing platforms exist to support various monitoring needs together with state-of-the-art power and communication capabilities. To be fit-for-purpose, sensors must withstand the challenging marine environment and provide data at an acceptable cost. Significant technological advancements have catalyzed the development of new and improved sensors for coastal and oceanographic applications. Sensors are becoming smaller, smarter, more cost-effective, and increasingly specialized and diversified. This article, therefore, provides a review of the state-of-the art oceanographic and coastal sensors. Progress in sensor development is discussed in terms of performance and the key strategies used for achieving robustness, marine rating, cost reduction, and antifouling protection.

Recent advances of sensing strategies for the detection of β-glucuronidase activity

β-Glucuronidase (β-GLU), a kind of hydrolase, is widely distributed in mammalian tissues, body fluids, and microbiota. Abnormal changes of β-GLU activity are often correlated with the occurrence of diseases and deterioration of water quality. Therefore, detection of β-GLU activity is of great significance in biomedicine and environmental health such as cancer diagnosis and water monitoring. However, the conventional β-GLU activity assay suffers from the limitations of low sensitivity, poor accuracy, and complex procedure. With the development of analytical chemistry, many advances have been made in the detection of β-GLU activity in recent years. The sensors for β-GLU activity detection which have the advantages of rapid and reliable detection have been attracting increased attentions. In this paper, the principles, performances, and limitations of these β-GLU sensors, including colorimetric sensing, fluorescent sensing, electrochemical sensing for the determination of β-GLU activity, have been summarized and discussed. Moreover, the challenges and research trends of β-GLU activity assay are proposed.

Unveiling the Virulent Genotype and Unusual Biochemical Behavior of Escherichia coli ST59

Extraintestinal pathogenic Escherichia coli (ExPEC) is a leading cause of human and animal infections worldwide. The utilization of selective and differential media to facilitate the isolation and identification of E. coli from complex samples, such as water, food, sediment, and gut tissue, is common in epidemiological studies. During a surveillance study, we identified an E. coli strain isolated from human blood culture that displayed atypical light cream-colored colonies in chromogenic agar and was unable to produce β-glucuronidase and β-galactosidase in biochemical tests. Genomic analysis showed that the strain belongs to sequence type 59 (ST59) and phylogroup F. The evaluation in silico of 104 available sequenced lineages of ST59 complex showed that most of them belong to serotype O1:K1:H7, are β-glucuronidase negative, and harbor a virulent genotype associated with the presence of important virulence markers such as pap, kpsE, chuA, fyuA, and yfcV. Most of them were isolated from extraintestinal human infections in diverse countries worldwide and could be clustered/subgrouped based on papAF allele analysis. Considering that all analyzed strains harbor a virulent genotype and most do not exhibit biochemical behavior typical of E. coli, we report that they could be misclassified or underestimated, especially in epidemiological studies where the screening criteria rely only on typical biochemical phenotypes, as happens when chromogenic media are used. IMPORTANCE The use of selective and differential media guides presumptive bacterial identification based on specific metabolic traits that are specific to each bacterial species. When a bacterial specimen displays an unusual phenotype in these media, this characteristic may lead to bacterial misidentification or a significant delay in its identification, putting a patient at risk depending on the infection type. In the present work, we describe a virulent E. coli sequence type (ST59) that does not produce beta-glucuronidase (GUS negative), production of which is the metabolic trait widely used for E. coli presumptive identification in diverse differential media. The recognition of this unusual metabolic trait may help in the proper identification of ST59 isolates, the identification of their reservoir, and the evaluation of the frequency of these pathogens in places where automatic identification methods are not available.

Label-free E. coli detection based on enzyme assay and a microfluidic slipchip

An enzyme assay based method in a microfluidic slipchip was proposed for the rapid and label-free detection of E. coli. The specific target analyte of E. coli was β-d-glucuronidase (GUS) which could catalyze the substrate 6-chloro-4-methyl-umbelliferyl-β-d-glucuronide (6-CMUG) to release the fluorescent molecule 6-chloro-4-methyl-umbelliferyl (6-CMU). E. coli culture, lysis and enzymatic reaction steps could be conducted in a microfluidic slipchip without any pumps and valves, which was tailored for fluorescence detection using a commercial plate reader, to achieve a rapid E. coli test. A mixture of the culture broth, enzyme inducer and E. coli was injected into the chambers on the top layer. A mixture of the substrate and lysis solution was injected into the chambers on the bottom layer. Then, the slipchip was slid to make each chamber independent. E. coli was cultured in the chamber in the LB broth for 2.5 h. After that, the slipchip was slid again to introduce the lysis solution into the culture solution for GUS release and enzyme reaction, and then incubated in the plate reader at 42 °C for another 2.5 h. During incubation, the fluorescence intensity of each chamber was recorded. This proposed label-free method can directly detect E. coli with a low concentration of 8 CFU per chamber within 5 h, thus showing great potential in on-site E. coli detection.

Simple enumeration of Escherichia coli concentrations in river water samples by measuring β-d-glucuronidase activities in a microplate reader

Monitoring of Escherichia coli concentrations in river water (RW) is essential to identify fecal pollution of the river. The objective of this study was to assess the suitability of a novel, simple and high throughput method developed in our laboratory to enumerate E. coli concentrations in RW samples. The method is based on the use of the synthetic substrate specific for the β-d-glucuronidase (GUS) produced by E. coli. GUS activities and E. coli concentrations were monitored at eight selected sites in rivers running through Sapporo, Japan. Because the fluorescence intensities of the synthetic substrate in the RW samples increased linearly over a 4-h incubation period, we could estimate the GUS activities of the RW samples. The GUS activities were highly correlated with E. coli concentrations at >100 most probable numbers 100 mL^-1 with a correlation coefficient of 0.87. The GUS activities of the RW samples collected from all sampling sites fitted well to a single correlation equation, which indicates that it was applicable to the estimation of E. coli concentrations regardless of the sampling sites. This method is simple, rapid, reliable, inexpensive, and high throughput, and is therefore useful for monitoring E. coli in RW.

Monitoring Approaches for Faecal Indicator Bacteria in Water: Visioning a Remote Real-Time Sensor for E. coli and Enterococci

A comprehensive review was conducted to assess the current state of monitoring approaches for primary faecal indicator bacteria (FIB) E. coli and enterococci. Approaches were identified and examined in relation to their accuracy, ability to provide continuous data and instantaneous detection results, cost, environmental awareness regarding necessary reagent release or other pollution sources, in situ monitoring capability, and portability. Findings showed that several methods are precise and sophisticated but cannot be performed in real-time or remotely. This is mainly due to their laboratory testing requirements, such as lengthy sample preparations, the requirement for expensive reagents, and fluorescent tags. This study determined that portable fluorescence sensing, combined with advanced modelling methods to compensate readings for environmental interferences and false positives, can lay the foundations for a hybrid FIB sensing approach, allowing remote field deployment of a fleet of networked FIB sensors that can collect high-frequency data in near real-time. Such sensors will support proactive responses to sudden harmful faecal contamination events. A method is proposed to enable the development of the visioned FIB monitoring tool.

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.

Demonstration of an optical biosensor for the detection of faecal indicator bacteria in freshwater and coastal bathing areas

ColiSense, an early warning system developed for Escherichia coli detection, is assessed using environmental samples. The system relies on the detection of β-glucuronidase (GUS), a biomarker enzyme for E. coli. In contrast with other rapid GUS-based methods, ColiSense is the only method that uses 6-chloro-4-methyl-umbelliferyl-β-D-glucuronide (6-CMUG) as a fluorogenic substrate. The system measures a direct kinetic response of extracted GUS, and the detection was carried out in the absence of particles or bacteria. It is necessary to evaluate the system with environmental samples to establish the relationship between faecal indicator bacteria E. coli and the response measured by the ColiSense. This paper presents the results of tests carried out with the ColiSense system for 2 trials, one conducted with freshwater samples collected from rivers in the Dublin area and a second conducted with seawater samples from coastal areas collected over the bathing season. A positive linear correlation was found between E. coli (MPN 100 mL^-1) and ColiSense response (R² = 0.85, N = 125, p < 0.01) for the seawater sample. A ColiSense response threshold was identified as 0-1.8 pmol min^-1 100 mL^-1, equivalent to 0-500 E. coli 100 mL^-1. Using this threshold, 96.8% of the samples were correctly classified as being above or below 500 E. coli 100 mL^-1 by the ColiSense system. Results presented demonstrate that the ColiSense system can be used as an early warning tool with potential for active management of bathing areas by providing results in 75 min from sample collection.

The effect of growth medium on an Escherichia coli pathway mirrored into GC/MS profiles

Escherichia coli (E. coli) is a Gram-negative coliform bacterium that is commonly found in the lower intestine of warm-blooded organisms. Most of the strains are harmless but some serotypes are pathogenic, meaning they can cause illness, either diarrhea or illness outside the intestinal tract. The aim of this work is to assess which components are generated for the purpose of E. coli target analysis. In this study, we intend to emphasize the importance of cultivability and to prove that growth media plays a crucial role in bacteria growth. To do this, E. coli was cultivated in three different growth mediums: (a) trypcase soy broth (TSB), (b) Mueller Hinton (MH), and (c) minimal salts (M9) enriched with glucose, respectively. Solid phase micro extraction was used as a sampling method, followed by gas chromatography-mass spectrometry for subsequent analysis. The relevant microbial volatile organic compounds (MVOCs) released in the headspace over the cultures of the E. coli bacteria and the afferent metabolic processes that occur in order to generate these compounds are presented in this work. The characteristic volatile compounds found in E. coli strain emissions were indole, phenylethyl alcohol and a series of esters when it was grown in TSB. Different pyrazines were found (pyrazine, 2-ethyl-3,5-dimethyl-, pyrazine, 2,5-dimethyl- and pyrazine, trimethyl-) when it was cultivated in MH. Long-chain alcohols such as 2-pentadecanol, 9-tetradecen-1-ol and 11-hexadecenol occurred in M9. Dimethyl disulfide, dimethyl trisulfide and a consistent number of alcohols and ketones were observed for E. coli cultivated in all three growth mediums. The occurrence and biosynthesis of these MVOCs clearly denote that the growth media used plays a crucial role in bacterial cultivation. The biomarker chemicals documented from this work may ultimately be used to identify bacterial infections by analyzing exhaled breath.