Marine bacteria cause false-positive results in the Colilert-18 rapid identification test for Escherichia coli in Florida waters

Evaluation of a Tetracycline-Resistant E. coli Enumeration Method for Correctly Classifying E. coli in Environmental Waters in Kentucky, USA

The global concern over antimicrobial resistance (AMR) and its impact on human health is evident, with approximately 4.95 million annual deaths attributed to antibiotic resistance. Regions with inadequate water, sanitation, and hygiene face challenges in responding to AMR threats. Enteric bacteria, particularly E. coli, are common agents linked to AMR-related deaths (23% of cases). Culture-based methods for detecting tetracycline-resistant E. coli may be of practical value for AMR monitoring in limited resource environments. This study evaluated the ColiGlow™ method with tetracycline for classifying tetracycline-resistant E. coli. A total of 61 surface water samples from Kentucky, USA (2020-2022), provided 61 presumed E. coli isolates, of which 28 isolates were obtained from tetracycline-treated media. Species identification and tetracycline resistance evaluation were performed. It was found that 82% of isolates were E. coli, and 18% were other species; 97% were identified as E. coli when using the API20E identification system. The MicroScan system yielded Enterobacter cloacae false positives in 20% of isolates. Adding tetracycline to ColiGlow increased the odds of isolating tetracycline-resistant E. coli 18-fold. Tetracycline-treated samples yielded 100% tetracycline-resistant E. coli when the total E. coli densities were within the enumeration range of the method. ColiGlow with tetracycline shows promise for monitoring tetracycline-resistant E. coli in natural waters and potentially aiding AMR surveillance in resource-limited settings among other environments.

PCR-based detection of pathogens in improved water sources: a scoping review protocol of the evidence in low-income and middle-income countries

INTRODUCTION

Occurrence of diverse human enteric bacterial, viral and protozoal pathogens in improved drinking water because of pathogenic microbial contamination is of increasing public health concern, particularly in low-income and middle-income countries (LMICs). Detecting microbial pathogens in water supplies comprehensively and accurately is beneficial to ensure the safety of water in LMICs where water contamination is a major concern. Application of PCR-based methods in detecting the microbial quality of water provides more accurate, sensitive and rapid outcomes over conventional methods of microbial identification and quantification. Therefore, exploring water quality outcomes generated through PCR-based methods is important to better understand the status and monitor progress towards internationally set goals for LMICs. This scoping review aims to map the existing evidence on the magnitude and characteristics of diarrhoeagenic pathogens as detected by PCR-based methods in improved water sources within the context of LMICs.

METHODS AND ANALYSIS

This study will be undertaken in line with the Joanna Briggs Institute (JBI) methodology for scoping reviews. We will consider the available publications covering PCR-based microbial water quality assessment of improved drinking water sources in LMICs. Searches will be undertaken in PubMed/Medline, Scopus, Web of Science, JBI, Cochrane Library and Google Scholar. A grey literature search will be conducted in Google and ProQuest.

ETHICS AND DISSEMINATION

The College of Natural and Computational Science Institution Review Board of Addis Ababa University gave formal ethical approval to this study protocol. The findings of this study will be disseminated to the concerned body through peer-reviewed publications, presentations and summaries.

Assessing the Water Pollution of the Brahmaputra River Using Water Quality Indexes

Water quality is continuously affected by anthropogenic and environmental conditions. A significant issue of the Indian rivers is the massive water pollution, leading to the spreading of different diseases due to its daily use. Therefore, this study investigates three aspects. The first one is testing the hypothesis of the existence of a monotonic trend of the series of eight water parameters of the Brahmaputra River recorded for 17 years at ten hydrological stations. When this hypothesis was rejected, a loess trend was fitted. The second aspect is to assess the water quality using three indicators (WQI)-CCME WQI, British Colombia, and a weighted index. The third aspect is to group the years and the stations in clusters used to determine the regional (spatial) and temporal trend of the WQI series, utilizing a new algorithm. A statistical analysis does not reject the hypothesis of a monotonic trend presence for the spatially distributed data but not for the temporal ones. Hierarchical clustering based on the computed WQIs detected two clusters for the spatially distributed data and two for the temporal-distributed data. The procedure proposed for determining the WQI temporal and regional evolution provided good results in terms of mean absolute error, root mean squared error (RMSE), and mean absolute percentage error (MAPE).

Comparison of the ColiPlate™ Kit with Two Common E. coli Enumeration Methods for Water

Quantitatively assessing fecal indicator bacteria in drinking water from limited resource settings (e.g., disasters, remote areas) can inform public health strategies for reducing waterborne illnesses. This study aimed to compare two common approaches for quantifying Escherichia coli (E. coli) density in natural water versus the ColiPlate™ kit approach. For comparing methods, 41 field samples from natural water sources in Kentucky (USA) were collected. E. coli densities were then determined by (1) membrane filtration in conjunction with modified membrane-thermotolerant E. coli (mTEC) agar, (2) Idexx Quanti-Tray® 2000 with the Colilert® substrate, and (3) the Bluewater Biosciences ColiPlate kit. Significant correlations were observed between E. coli density data for all three methods (p < 0.001). Paired t-test results showed no difference in E. coli densities determined by all the methods (p > 0.05). Upon assigning modified mTEC as the reference method for determining the World Health Organization-assigned “very high-risk” levels of fecal contamination (>100 E. coli CFU/100 mL), both ColiPlate and Colilert exhibited excellent discrimination for screening very high-risk levels according to the area under the receiver operating characteristic curve (~89%). These data suggest ColiPlate continues to be an effective monitoring tool for quantifying E. coli density and characterizing fecal contamination risks from water.

Growth and antibiotic resistance acquisition of Escherichia coli in a river that receives treated sewage effluent

Wastewater treatment plants could discharge Escherichia coli and antibiotic resistant bacteria to the environment adjacent to, or downstream of their discharge point. However, their discharge also contains nutrients which could promote growth of E. coli in water environments. This study was done to clarify the potential of growth and antibiotic resistance acquisition of E. coli in a river environment. Levels of E. coli were monitored in a river that receives treated sewage effluent for over four years. River water, periphyton and sediment samples were collected at sites upstream and downstream of treated sewage inflow. Concentrations of E. coli increased in river water and periphyton at the sites downstream of the treated sewage inflow, although levels of E. coli were very low or below detection limit in the treated sewage samples. Concentrations of Chlorophyll a increased at the downstream sites, likely due to nutrient input from the treated sewage. Based on pulsed field gel electrophoresis, identical genotype occurred at multiple sites both upstream and downstream of the treated sewage inflow. However, strains resistant to antibiotics such as ampicillin, cefazolin, ciprofloxacin, and chloramphenicol were more frequently obtained from the downstream sites than the upstream sites. Multidrug resistant E. coli strains were detected in periphyton and sediment samples collected at the downstream sites. Non-resistant strains with PDGE genotype identical to the multi-drug strains were also detected, indicating that E. coli might have become resistant to antibiotics by acquiring resistance genes via horizontal gene transfer. Laboratory incubation experiment showed the growth of E. coli in periphyton or sediment-fed river water samples. These results suggest that the wastewater treatment inflow did not directly provide E. coli to the river water, but could promote the growth of periphyton, which could lead to the elevated levels of E. coli and the emergence of antibiotic resistant E. coli.

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.

Hydroxyapatite powder cake filtration reduces false positives associated with halophilic bacteria when evaluating Escherichia coli in seawater using Colilert-18

Escherichia coli is an important fecal indicator bacterium that is used to evaluate the microbiological quality of water. The Colilert-18 (Quanti-Tray/2000) is a widely used, rapid, and simple quantitative method for detecting E. coli in drinking water, bathing water, and wastewater. However, Colilert-18 method is less reliable for seawater; false positives are often caused by halophilic bacteria such as Vibrio. While false positives can be avoided by diluting the sample by 10 times or more, the resulting decrease in detection limit makes it difficult to quantify E. coli in seawater. In this study, we combined cake filtration, using hydroxyapatite powder, with the Colilert-18 method to remove salinity without diluting the water sample. When quantifying E. coli in river water, the E. coli concentration obtained from the cake filtration/Colilert-18 method showed a high quantitative value of 90% or more, on average, compared to the concentration obtained with the original Colilert-18 method. The E. coli concentrations in seawater determined using the developed method were similar to those determined using the modified m-TEC method, with no false positives. Highly reliable quantitative values can be obtained using the proposed method because it is possible to measure 100 times as much sample compared to the dilution method. Thus, the developed method is expected to be a powerful tool that can eliminate the problem of false positives.

[A protocol for evaluating the probability of the recreational use of rivers and its application in risk analysis]

Contaminated waters constitute health risks not only due to direct consumption, but also in recreational use. Risk analysis strategies aim to reduce the instances of contaminations and must include the population's perceptions and willingness to assume risks. A rapid and simple method was developed to evaluate the probability of use of recreational waters. Interviews were conducted in municipalities with different ecological conditions, in order to define the factors used by people to decide to use, or otherwise, river waters. After analyzing the results, the "Índice de Probabilidade de Uso Recreativo de Águas (I-PURA)" was elaborated and tested. The index was then employed at 26 river locations representing five of the nine hydrographic regions of Rio de Janeiro state. The frequency of use, water contamination and a Habitat Assessment Visual Index (IAH) was also measured. The I-PURA was correlated with the frequency of use. Furthermore, the I-PURA was not correlated with IAH, showing that user perceptions are different from purely ecological aspects. This tool offers useful information for risk assessment and environmental management. Sites with a high probability of use, or observed use, that are highly contaminated should be prioritized for interventions.

Coliform Bacteria Monitoring in Fish Systems: Current Practices in Public Aquaria

Public aquaria evaluate coliform indicator bacteria levels in fish systems, but the purpose of testing, testing methods, and management responses are not standardized, unlike with the coliform bacteria testing for marine mammal enclosures required by the U.S. Department of Agriculture. An online survey was sent to selected aquaria to document current testing and management practices in fish systems without marine mammals. The information collected included indicator bacteria species, the size and type of systems monitored, the primary purpose of testing, sampling frequency, test methods, the criteria for interpreting results, corrective actions, and management changes to limit human exposure. Of the 25 institutions to which surveys were sent, 19 (76%) responded. Fourteen reported testing for fecal indicator bacteria in fish systems. The most commonly tested indicator species were total (86%) and fecal (79%) coliform bacteria, which were detected by means of the membrane filtration method (64%). Multiple types and sizes of systems were tested, and the guidelines for testing and corrective actions were highly variable. Only three institutions performed additional tests to confirm the identification of indicator organisms. The results from this study can be used to compare bacterial monitoring practices and protocols in fish systems, as an aid to discussions relating to the accuracy and reliability of test results, and to help implement appropriate management responses. Received August 23, 2015; accepted December 29, 2015.

Evaluation of simple diffusion chlorinators for decontamination of wells in a rural settlement in Amazonia, Brazil

While the Amazon region has the world's largest reserve of fresh water, the lack of water services and water treatment, especially in non-urban regions, causes environmental and health problems. In isolated rural settlements supply is usually by shallow wells, and the quality of water is a concern for residents. These are situations where there are restricted options for water treatment. This study aimed to assess the use of simplified diffusion chlorinators as an alternative water treatment method. Bacteriological analyses were made of 100 samples of water from the wells, before and after application of the chlorinators, in the Rural Settlement of Rio Pardo, Presidente Figueiredo in the Brazilian State of Amazonas. The sources that were analyzed were considered inappropriate for consumption without prior treatment, and the use of the chlorinators eliminated all contamination by thermotolerant coliforms in the great majority of cases. Also, the method was well received by residents, because it does not leave a taste in the water, is relatively low-cost and handling is easy. We discuss the advantages and limitations of the use of this method of treatment for this social-environmental context and present suggestions for improvement and adaptation, for application of this methodology in other settlements.

Comparison of Colilert-18 with miniaturised most probable number method for monitoring of Escherichia coli in bathing water

The purpose of this equivalence study was to compare an alternative method, Colilert-18 Quanti-Tray (ISO 9308-2) with the European bathing water directive (2006/7/EC) reference method, the miniaturised most probable number (MMPN) method (ISO 9308-3), for the analysis of Escherichia coli. Six laboratories analysed a total of 263 bathing water samples in Finland. The comparison was carried out according to ISO 17994:2004. The recovery of E. coli using the Colilert-18 method was 7.0% and 8.6% lower than that of the MMPN method after 48 hours and 72 hours of incubation, respectively. The confirmation rate of presumptive E. coli-positive wells in the Colilert-18 and MMPN methods was high (97.8% and 98.0%, respectively). However, the testing of presumptive E. coli-negative but coliform bacteria-positive (yellow but not fluorescent) Colilert-18 wells revealed 7.3% false negative results. There were more false negatives in the naturally contaminated waters than in the samples spiked with waste water. The difference between the recovery of Colilert-18 and the MMPN method was considered not significant, and subsequently the methods are considered as equivalent for bathing water quality monitoring in Finland. Future bathing water method equivalence verification studies may use the data reported herein. The laboratories should make sure that any wells showing even minor fluorescence will be determined as positive for E. coli.

Impact of seasonal variation on Escherichia coli concentrations in the riverbed sediments in the Apies River, South Africa

Many South Africans living in resource-poor settings with little or no access to pipe-borne water still rely on rivers as alternative water sources for drinking and other purposes. The poor microbial quality of such water bodies calls for appropriate monitoring. However, routine monitoring only takes into consideration the microbial quality of the water column, and does not include monitoring of the riverbed sediments for microbial pollution. This study sought to investigate the microbial quality of riverbed sediments in the Apies River, Gauteng Province, South Africa, using Escherichia coli as a faecal indicator organism and to investigate the impact of seasonal variation on its abundance. Weekly samples were collected at 10 sampling sites on the Apies River between May and August 2013 (dry season) and between January and February 2014 (wet season). E. coli was enumerated using the Colilert®-18 Quanti-Tray® 2000 system. All sites tested positive for E. coli. Wastewater treatment work effluents had the highest negative impact on the river water quality. Seasonal variations had an impact on the concentration of E. coli both in water and sediments with concentrations increasing during the wet season. A strong positive correlation was observed between temperature and the E. coli concentrations. We therefore conclude that the sediments of the Apies River are heavily polluted with faecal indicator bacteria and could also harbour other microorganisms including pathogens. The release of such pathogens into the water column as a result of the resuspension of sediments due to extreme events like floods or human activities could increase the health risk of the populations using the untreated river water for recreation and other household purposes. There is therefore an urgent need to reconsider and review the current South African guidelines for water quality monitoring to include sediments, so as to protect human health and other aquatic lives.

On the track for an efficient detection of Escherichia coli in water: A review on PCR-based methods

Ensuring water safety is an ongoing challenge to public health providers. Assessing the presence of fecal contamination indicators in water is essential to protect public health from diseases caused by waterborne pathogens. For this purpose, the bacteria Escherichia coli has been used as the most reliable indicator of fecal contamination in water. The methods currently in use for monitoring the microbiological safety of water are based on culturing the microorganisms. However, these methods are not the desirable solution to prevent outbreaks as they provide the results with a considerable delay, lacking on specificity and sensitivity. Moreover, viable but non-culturable microorganisms, which may be present as a result of environmental stress or water treatment processes, are not detected by culture-based methods and, thus, may result in false-negative assessments of E. coli in water samples. These limitations may place public health at significant risk, leading to substantial monetary losses in health care and, additionally, in costs related with a reduced productivity in the area affected by the outbreak, and in costs supported by the water quality control departments involved. Molecular methods, particularly polymerase chain reaction-based methods, have been studied as an alternative technology to overcome the current limitations, as they offer the possibility to reduce the assay time, to improve the detection sensitivity and specificity, and to identify multiple targets and pathogens, including new or emerging strains. The variety of techniques and applications available for PCR-based methods has increased considerably and the costs involved have been substantially reduced, which together have contributed to the potential standardization of these techniques. However, they still require further refinement in order to be standardized and applied to the variety of environmental waters and their specific characteristics. The PCR-based methods under development for monitoring the presence of E. coli in water are here discussed. Special emphasis is given to methodologies that avoid pre-enrichment during the water sample preparation process so that the assay time is reduced and the required legislated sensitivity is achieved. The advantages and limitations of these methods are also reviewed, contributing to a more comprehensive overview toward a more conscious research in identifying E. coli in water.

Genotypic and phenotypic characterization of Escherichia coli isolates from feces, hands, and soils in rural Bangladesh via the Colilert Quanti-Tray System

The increased awareness of the role of environmental matrices in enteric disease transmission has resulted in the need for rapid, field-based methods for fecal indicator bacteria and pathogen detection. Evidence of the specificity of β-glucuronidase-based assays for detection of Escherichia coli from environmental matrices relevant to enteric pathogen transmission in developing countries, such as hands, soils, and surfaces, is limited. In this study, we quantify the false-positive rate of a β-glucuronidase-based E. coli detection assay (Colilert) for two environmental reservoirs in Bangladeshi households (hands and soils) and three fecal composite sources (cattle, chicken, and humans). We investigate whether or not the isolation source of E. coli influences phenotypic and genotypic characteristics. Phenotypic characteristics include results of biochemical assays provided by the API-20E test; genotypic characteristics include the Clermont phylogroup and the presence of enteric and/or environmental indicator genes sfmH, rfaI, and fucK. Our findings demonstrate no statistically significant difference in the false-positive rate of Colilert for environmental compared to enteric samples. E. coli isolates from all source types are genetically diverse, representing six of the seven phylogroups, and there is no difference in relative frequency of phylogroups between enteric and environmental samples. We conclude that Colilert, and likely other β-glucuronidase-based assays, is appropriate for detection of E. coli on hands and in soils with low false-positive rates. Furthermore, E. coli isolated from hands and soils in Bangladeshi households are diverse and indistinguishable from cattle, chicken, and human fecal isolates, using traditional biochemical assays and phylogrouping.

Microbial quality and phylogenetic diversity of fresh rainwater and tropical freshwater reservoir

The impact of rainwater on the microbial quality of a tropical freshwater reservoir through atmospheric wet deposition of microorganisms was studied for the first time. Reservoir water samples were collected at four different sampling points and rainwater samples were collected in the immediate vicinity of the reservoir sites for a period of four months (January to April, 2012) during the Northeast monsoon period. Microbial quality of all fresh rainwater and reservoir water samples was assessed based on the counts for the microbial indicators: Escherichia coli (E. coli), total coliforms, and Enterococci along with total heterotrophic plate counts (HPC). The taxonomic richness and phylogenetic relationship of the freshwater reservoir with those of the fresh rainwater were also assessed using 16 S rRNA gene clone library construction. The levels of E. coli were found to be in the range of 0 CFU/100 mL – 75 CFU/100 mL for the rainwater, and were 10–94 CFU/100 mL for the reservoir water. The sampling sites that were influenced by highway traffic emissions showed the maximum counts for all the bacterial indicators assessed. There was no significant increase in the bacterial abundances observed in the reservoir water immediately following rainfall. However, the composite fresh rainwater and reservoir water samples exhibited broad phylogenetic diversity, including sequences representing Betaproteobacteria, Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Lentisphaerae and Bacteriodetes. Members of the Betaproteobacteria group were the most dominant in both fresh rainwater and reservoir water, followed by Alphaproteobacteria, Sphingobacteria, Actinobacteria and Gammaproteobacteria.

Fast coliform detection in portable microbe enrichment unit (PMEU) with Colilert(®) medium and bubbling

Laboratory strains of coliforms Escherichia coli and Klebsiella mobilis were used to artificially contaminate water samples in two different cultivation and detection systems, without and with bubble flow. Samples were collected with an automated system (ASCS). The positive coliform signal caused the color change into yellow (at 550-570nm). This signal could also be transmitted on-line to cell phones. E. coli containing samples emitted UV fluorescence at 480-560nm when activated by UV light. If cultivation was started with inocula varying from 10,000 to 1cfu/ml, the positive detection was obtained between 2 and 18h, respectively, in Colilert medium using Coline PMEU device without gas bubbling. Accordingly, a single K. mobilis cell produced detectable growth in 18h. Various clinical E. coli strains were compared to each other with equal inoculum sizes, and they showed slight variations in the initiation and speed of growth. The gas bubble flow in PMEU Spectrion promoted the mixing and interaction of bacteria and indicator media and speeded the onset of growth. Carbon dioxide also accelerated bacterial growth. In the presence of vancomycin, the onset of E. coli culture growth was speeded up by the volatile outlet flow from previous cultures. In the last cultivation syringe in a series of five, the lag phase disappeared and the growth of the inoculum continued without major interruption.

IN CONCLUSION

the stimulation of the cultures by the gas flow turned out to be a useful means for improving the detection of indicator bacteria. It could also be used in combination with antibiotic selection in the broth medium.

Fecal pathogen pollution: sources and patterns in water and sediment samples from the upper Cook Inlet, Alaska ecosystem

Fecal pathogens are transported from a variety of sources in multi-use ecosystems such as upper Cook Inlet (CI), Alaska, which includes the state's urban center and is highly utilized by humans and animals. This study used a novel water quality testing approach to evaluate the presence and host sources of potential fecal pathogens in surface waters and sediments from aquatic ecosystems in upper CI. Matched water and sediment samples, along with effluent from a municipal wastewater treatment facility, were screened for Salmonella spp., Vibrio spp., Cryptosporidium spp., Giardia spp., and noroviruses. Additionally, Bacteroidales spp. for microbial source tracking, and the fecal indicator bacteria Enterococcus spp. as well as fecal coliforms were evaluated. Overall, Giardia and Vibrio were the most frequently detected potential pathogens, followed by Cryptosporidium and norovirus, while Salmonella was not detected. Sample month, matrix type, and recent precipitation were found to be significant environmental factors for protozoa or host-associated Bacteroidales marker detection, whereas location and water temperature were not. The relative contribution of host-associated markers to total fecal marker concentration was estimated using a Monte Carlo method, with the greatest relative contribution to the Bacteroidales marker concentration coming from human sources, while the remainder of the universal fecal host source signal was uncharacterized by available host-associated assays, consistent with wildlife fecal sources. These findings show how fecal indicator and pathogen monitoring, along with identifying contributing host sources, can provide evidence of coastal pathogen pollution and guidance as to whether to target human and/or animal sources for management.

Microbial monitoring of surface water in South Africa: an overview

Infrastructural problems force South African households to supplement their drinking water consumption from water resources of inadequate microbial quality. Microbial water quality monitoring is currently based on the Colilert®18 system which leads to rapidly available results. Using Escherichia coli as the indicator microorganism limits the influence of environmental sources on the reported results. The current system allows for understanding of long-term trends of microbial surface water quality and the related public health risks. However, rates of false positive for the Colilert®18-derived concentrations have been reported to range from 7.4% to 36.4%. At the same time, rates of false negative results vary from 3.5% to 12.5%; and the Colilert medium has been reported to provide for cultivation of only 56.8% of relevant strains. Identification of unknown sources of faecal contamination is not currently feasible. Based on literature review, calibration of the antibiotic-resistance spectra of Escherichia coli or the bifidobacterial tracking ratio should be investigated locally for potential implementation into the existing monitoring system. The current system could be too costly to implement in certain areas of South Africa where the modified H(2)S strip test might be used as a surrogate for the Colilert®18.

Fluorescence spectroscopy as a tool for determining microbial quality in potable water applications

Building on previous work where fluorescence spectroscopy has been used to detect sewage in rivers, a portable LED spectrophotometer was used for the first time to establish bacterial numbers in a range of water samples. A mixed-method approach was used with standard bacteria enumeration techniques on diluted river water and sewage works final effluent using a number of diluents (Ringer's solution, tap water and potable spring water). Fluorescence from uncultured dilutions was detected at a 280 nm excitation/360 nm emission wavelength (corresponding to the region of tryptophan and indole fluorescence) and compared with bacteria numbers on the same cultured sample. Good correlations were obtained for total coliforms, E. coli and heterotrophic bacteria with the portable LED spectrophotometer (R2 = 0.78, 0.72 and 0.81 respectively). The results indicate that the portable spectrophotometer could be applied to establish the quality of drinking water in areas of poor sanitation that are subject to faecal contamination, where infrastructure failure has occurred in the supply of clean drinking water. This would be particularly useful where laboratory facilities are not at hand.

Cultivation-independent analysis of bacteria in IDEXX Quanti-Tray/2000 fecal indicator assays

Monitoring microbiological water quality is important for protecting water resources and the health of swimmers. Routine monitoring relies on cultivating fecal indicator bacteria (FIB), frequently using defined substrate technology. Defined substrate technology is designed to specifically enrich for FIB, but a complete understanding of the assay microbiology requires culture-independent analysis of the enrichments. This study aimed to identify bacteria in positive wells of Colilert and Enterolert Quanti-Tray/2000 (IDEXX Laboratories) FIB assays in environmental water samples and to quantify the degree of false-positive results for samples from an urban creek by molecular methods. Pooled Escherichia coli- and Enterococcus-positive Quanti-Tray/2000 enrichments, either from urban creek dry weather flow or municipal sewage, harbored diverse bacterial populations based on 16S rRNA gene sequences and terminal restriction fragment length polymorphism analyses. Target taxa (coliforms or enterococci) and nontarget taxa (Vibrio spp., Shewanella spp., Bacteroidetes, and Clostridium spp.) were identified in pooled and individual positive Colilert and Enterolert wells based on terminal restriction fragments that were in common with those generated in silico from clone sequences. False-positive rates of between 4 and 23% occurred for the urban creek samples, based on the absence of target terminal restriction fragments in individual positive wells. This study suggests that increased selective inhibition of nontarget bacteria could improve the accuracy of the Colilert and Enterolert assays.

A novel screening method for competitive FRET-aptamers applied to E. coli assay development

A novel high-throughput screening method is described in which a family of DNA aptamers selected against E. coli outer membrane proteins (OMPs) is subjected to PCR in the presence of fluorophore-dUTP conjugates using Deep Vent® exo- polymerase. The fluorophore-doped aptamers and their complementary strands are then heated to render them single-stranded and screened in filter well microtiter plates for fluorescence resonance energy transfer (FRET) assay potential. Using this system, a superior competitive FRET-aptamer designated EcO 4R was identified and the location of its putative binding pocket was determined by individually testing FRET potential in each of the secondary loop structures. By labeling the binding pocket with Alexa Fluor (AF) 647 and binding the aptamer to heavily Black Hole Quencher-3 (BHQ-3)-labeled E. coli bacteria, detection of as few as 30 live unlabeled E. coli per ml was achieved in a competitive displacement FRET assay format. The far red fluorescence emission enables detection in largely blue-green autofluorescent matrices. In addition, the competitive transfer of AF 647-EcO-4R aptamer to unlabeled E. coli cells after a 15 min equilibration period was verified by fluorescence microscopy. The present study also demonstrated that high aptamer affinity is not well correlated with competitive FRET potential.

Covalently linked immunomagnetic separation/adenosine triphosphate technique (Cov-IMS/ATP) enables rapid, in-field detection and quantification of Escherichia coli and Enterococcus spp. in freshwater and marine environments

AIMS

Developing a rapid method for detection of faecal pollution is among the critical goals set forth by the Environmental Protection Agency in its revision of water quality criteria. The purpose of this study is to devise and test covalently linked antibody-bead complexes for faecal indicator bacteria (FIB), specifically Escherichia coli or Enterococcus spp., in measuring water quality in freshwater and marine systems.

METHODS AND RESULTS

Covalently linked complexes were 58-89% more robust than antibody-bead complexes used in previous studies. Freshwater and marine water samples analysed using covalently linked immunomagnetic separation/adenosine triphosphate quantification technique (Cov-IMS/ATP) and culture-based methods yielded good correlations for E. coli (R = 0·87) and Enterococcus spp. (R = 0·94), with method detection limits below EPA recreational water quality health standards for single standard exceedances (E. coli- 38 cells per 100 ml; Enterococcus spp. - 25 cells per 100 ml). Cov-IMS/ATP correctly classified 87% of E. coli and 94% of Enterococcus spp. samples based on these water quality standards. Cov-IMS/ATP was also used as a field method to rapidly distinguish differential loading of E. coli between two stream channels to their confluence.

CONCLUSIONS

Cov-IMS/ATP is a robust, in-field detection method for determining water quality of both fresh and marine water systems as well as differential loading of FIB from two converging channels.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first work to present a viable rapid, in-field assay for measuring FIB concentrations in marine water environments. Cov-IMS/ATP is a potential alternative detection method, particularly in areas with limited laboratory support and resources, because of its increased economy and portability.

Space/time analysis of fecal pollution and rainfall in an eastern North Carolina estuary

The Newport River Estuary (NPRE) is a high-priority shellfish harvesting area in eastern North Carolina that is impaired due to fecal contamination, specifically exceeding recommended levels for fecal coliforms. A hydrologic-driven mean trend model was developed, as a function of antecedent rainfall, in the NPRE to predict levels of Escherichia coli (EC, measured as a proxyforfecal coliforms). This mean trend model was integrated in a Bayesian Maximum Entropy (BME) framework to produce informative space/time (S/T) maps depicting fecal contamination across the NPRE during winter and summer months. These maps showed that during dry winter months, corretponding to the oyster harvesting season in North Carolina (October 1-March 30), predicted EC concentrations were below the shellfish harvesting standard (14 MPN/100 mL). However, after substantial rainfall of 3.81 cm (1.5 in.), the NPRE did not appear to mee this requirement. Warmer months resulted in the predicted EC concentrations exceeding the threshold for the NPRE. Predicted ENT concentrations were generally below the recreational water quality threshold (104 MPN/100 mL), except for warmer months after substantial rainfall. Once established, this combined approach produces near real-time visual information on which to base water quality management decisions.

Performance of microbiological control by a point-of-use filter system for drinking water purification

Purification capacity of a faucet mounted type water filter for home use was evaluated, particularly with regard to microbiological performance under different running conditions. Biofilms were formed inside the filter, affecting the bacterial quality of the effluent water. Low flow rate, long stagnation period and high filter temperature were found favorable for bacterial growth inside. By commercial analytical profile index (API) kits, ten different bacterial species were identified in drinking water, four of which were probably contributed to the biofilm formation since they were also present in the biofilm. Fluorescence in situ hybridization (FISH) was used to confirm the API identification results, and direct viable count (DVC) method was employed to improve the sensitivity of FISH for the isolated Acinetobacter spp. and Pseudomonas putida as models. Relationship between the filter operating condition and the bacterial community alteration was partly revealed, which could provide the basic knowledge for the filter design and its practical use.

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.

Molecular identification of coliform bacteria isolated from drinking water reservoirs with traditional methods and the Colilert-18 system

The accuracy of a traditional method (lactose utilization with acid and gas production) for the detection of coliform bacteria and E. coli was tested in comparison with method ISO 9308-1 (based on acid formation from lactose) and the Colilert-18 system (detection of beta-galactosidase). A total of 345 isolates were identified after isolation from water samples using API 20E strips. The Colilert-18 led to the highest number of positive findings (95% of the isolates were assigned to coliforms), whereas the ISO-9308-1 method resulted only in 29% coliform findings. With the traditional method only 15% were rated positive. Most of the isolates were identified by the API 20E system as Enterobacter spp. (species of the Enterobacter cloacae complex), Serratia spp., Citrobacter spp.and Klebsiella spp.; but species identification remained vague in several cases. A more detailed identification of 126 pure cultures by using 16S rRNA gene sequence analysis and analysis of the hsp60 gene resulted in the identification of Enterobacter nimipressuralis, E. amnigenus, E. asburiae, E. hormaechei, and Serratia fonticola as predominat coliforms. These species are beta-galactosidase positive, but show acid formation from lactose often after a prolonged incubation time. They are often not of fecal origin and may interfere with the ability to accurately detect coliforms of fecal origin.

Use of salinity mixing models to estimate the contribution of creek water fecal indicator bacteria to an estuarine environment: Newport Bay, California

The contribution of freshwater discharge to fecal indicator bacteria (FIB) impairment of an estuarine environment can be approximated from simple, two end-member mixing models using salinity as a tracer. We conducted a yearlong time series investigation of Newport Bay, a regionally important estuarine embayment in southern California, assessing the concentrations of FIB, specifically Escherichia coli and enterococci bacteria, and salinity. In total, eight within-bay stations and one offshore control site were sampled nearly once per week and the three tributaries draining into Newport Bay were sampled approximately daily. Using salinity as a conservative tracer for water mass mixing and determining the end-member values of FIB in both the creek sites and the offshore site, we created a linear, two end-member mixing model of FIB within Newport Bay. Deviations from the mixing model suggest either an additional source of FIB to the bay (e.g. bird feces, storm drain discharge) or regrowth and/or die-off of FIB within the bay. Our results indicate that salinity mixing models can be useful in predicting changes in FIB concentrations in the estuarine environments and can help narrow the search for sources of FIB to the bay and enhance our understanding of the fate of FIB within the bay.

A comparison of bacterial indicators and methods in rural surface waters

The United States Environmental Protection Agency (USEPA) recommends the use of Escherichia coli (E. coli) and enterococci as indicators of enteric pathogens in fresh waters; however, fecal coliform analyses will remain important by virtue of the large amount of historic data collected in prior years. In this study, we attempted, in a real-world situation (i.e., a rural inland watershed in the Piedmont of South Carolina) to compare different bacterial indicators and methods to one another. We compared fecal coliforms, enumerated by membrane filtration with E. coli, enumerated by a commercialized enzyme substrate method and observed E. coli/fecal coliform ratios of 1.63 and 1.2 for two separate tests. In the same watershed, we observed an E. coli/fecal coliform ratio of 0.84 when we used the commercialized enzyme substrate method for both enumerations. Given these results, users of such data should exercise care when they make comparisons between historic membrane filtration data and data acquired through the use of the more modern enzymatic methods. Some sampling and side-by-side testing between methods in a specific watershed may be prudent before any conversion factors between old and new datasets are applied.

A long-term study comparing membrane filtration with Colilert defined substrates in detecting fecal coliforms and Escherichia coli in natural waters

Assessment methods for determining the presence and number of fecal bacteria and Escherichia coli (E. coli) in waters, foodstuffs, sewage effluent, and soils have evolved from multiple tube fermentations (MTF's) to membrane filtrations (MF's) to, most recently, defined substrate technologies (DST's). Mounting evidence indicates Colilert DST (IDEXX, Westbrook, ME) to be a versatile assessment technique for detecting and enumerating E. coli over a range of applications. This study compared the performance of Colilert DST with a confirmed standard MF technique using m-FC broth (Millipore, Bedford, MA) in assessing E. coli in ten different environmental water samples obtained monthly over a 3-year period from the upper Appomattox River, VA. For the duration of the study, E. coli counts measured by Colilert DST were positively correlated (Pearson's correlation coefficient=0.956; slope=0.979; p<0.0001) with E. coli counts measured by confirmed MF procedures. The results of a two-factor ANOVA revealed that Colilert DST counts compared equally to confirmed MF counts by year (p=0.974), by stream sampled (p=1.0), and by season (p=0.696). E. coli counts were significantly lower during cold season months (Dec/Jan/Feb) than during warm season months (Jun/Jul/Aug) for each year contributing to marked variation in sample quality. Counts obtained by Colilert DST compared equally to those obtained by MF across all samples and dates for the three years. Colilert DST presents a laboratory protocol that is simpler to manage, quicker to process, and easier to quantify results than MF. These factors, plus the enhanced precision and versatility of Colilert DST over the span of this three-year study attests to its suitability for testing ambient surface waters.

Evaluation of Colilert-18 for the detection of coliforms and Escherichia coli in tropical fresh water

AIMS

To evaluate the suitability of Colilert-18 in detecting Escherichia coli and total coliforms in tropical freshwater samples.

METHODS AND RESULTS

Target organisms were isolated from yellow-fluorescent and yellow wells of Colilert-18/Quanti-Tray using m-TEC agar and m-ENDO LES agar respectively. All the selected isolates were first identified based on their fatty acid methyl ester profile. Isolates showing contradictory results to that of the Colilert-18 procedure were re-identified using API 20E strips. A total of 357 isolates, 177 from yellow-fluorescent wells and 180 from yellow wells, were identified.

CONCLUSIONS

The false-positive and -negative rates for E. coli detection using Colilert-18 were 36.4% and 11%, respectively, while for coliform detection the false-positive rate was 10.3%.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high false-positive rate of Colilert-18, tempers its value for E. coli detection when used for tropical freshwater samples.

Comparison and verification of bacterial water quality indicator measurement methods using ambient coastal water samples

More than 30 laboratories routinely monitor water along southern California's beaches for bacterial indicators of fecal contamination. Data from these efforts frequently are combined and compared even though three different methods (membrane filtration (MF), multiple tube fermentation (MTF), and chromogenic substrate (CS) methods) are used. To assess data comparability and quantify variability within method and across laboratories, 26 laboratories participated in an intercalibration exercise. Each laboratory processed three replicates from eight ambient water samples employing the method or methods they routinely use for water quality monitoring. Verification analyses also were conducted on a subset of wells from the CS analysis to confirm or exclude the presence of the target organism. Enterococci results were generally comparable across methods. Confirmation revealed a 9% false positive rate and a 4% false negative rate in the CS method for enterococci, though these errors were small in the context of within- and among-laboratory variability. Fecal coliforms also were comparable across all methods, though CS underestimated the other methods by about 10%, probably because it measures only E. coli, rather than the larger fecal coliform group measured by MF and MTF. CS overestimated total coliforms relative to the other methods by several fold and was found to have a 40% false positive rate in verification. Across-laboratory variability was small relative to within- and among-method variability, but only after data entry errors were corrected. One fifth of the laboratories committed data entry errors that were much larger than any method-related errors. These errors are particularly significant because these data were submitted in a test situation where laboratories were aware they would be under increased scrutiny. Under normal circumstances, it is unlikely that these errors would have been detected and managers would have been obliged to issue beach water quality warnings.

Identifying pollutant sources in tidally mixed systems: case study of fecal indicator bacteria from marinas in Newport Bay, southern California

This study investigates the contribution of several marinas to fecal indicator bacteria impairment in Newport Bay, a regionally important tidal embayment in southern California. Three different fecal indicator bacteria groups were assayed, including total coliform, Escherichia coli, and enterococci bacteria, all measured using the IDEXX Colilert and Enterolert system. To document temporal variability in the fecal indicator bacteria signal, water column samples (n = 4132) were collected from two marinas over time scales ranging from hours to months. To document spatial variability of the fecal indicator bacteria signal, water column and sediment samples were collected from a number of sites (n = 11 to 36, depending on the study) in and around the two marinas, over spatial scales ranging from meters to kilometers. To identify the dominant temporal and spatial patterns in these data a statistical approach--Empirical Orthogonal Function analysis--was utilized. Finally, to clarify the transport pathways responsible for the observed temporal and spatial patterns, fecal indicator bacteria data were compared to simultaneous measurements of tidal flow, temperature, and salinity. The results of this field effort collectively implicate runoff--both dry weather runoff at sampling sites located near some storm drains and wet weather runoff at all sites--as a primary source of fecal indicator bacteria in the water column and subtidal sediments. The results and analysis presented here reinforce the growing body of evidence that management of fecal indicator bacteria impairment in the coastal waters of southern California will require developing long-term strategies for treating nonpoint sources of both dry weather and stormwater runoff.

Evaluation of Colilert-18 for detection of coliforms and Eschericha coli in subtropical freshwater

The accuracy of Colilert-18 as a test for coliforms and Escherichia coli in subtropical freshwater was evaluated by using API 20E strips and fatty acid methyl ester analysis. The false-positive and -negative rates of detection were 7.4 and 3.5%, respectively, for E. coli and 9.6 and 6.3%, respectively, for coliforms.

Scaling and management of fecal indicator bacteria in runoff from a coastal urban watershed in southern California

This paper describes a series of field studies aimed at identifying the spatial distribution and flow forcing of fecal indicator bacteria in dry and wet weather runoff from the Talbert watershed, a highly urbanized coastal watershed in southern California. Runoff from this watershed drains through tidal channels to a popular public beach, Huntington State Beach, which has experienced chronic surf zone water quality problems over the past several years. During dry weather, concentrations of fecal indicator bacteria are highest in inland urban runoff, intermediate in tidal channels harboring variable mixtures of urban runoff and ocean water, and lowest in ocean water at the base of the watershed. This inland-to-coastal gradient is consistent with the hypothesis that urban runoff from the watershed contributes to coastal pollution. On a year round basis, the vast majority (>99%) of fecal indicator bacteria loading occurs during storm events when runoff diversions, the management approach of choice, are not operating. During storms, the load of fecal indicator bacteria in runoff follows a power law of the form L approximately Qn, where L is the loading rate (in units of fecal indicator bacteria per time), Q is the volumetric flow rate (in units of volume per time), and the exponent n ranges from 1 to 1.5. This power law and the observed range of exponent values are consistent with the predictions of a mathematical model that assumes fecal indicator bacteria in storm runoff originate from the erosion of contaminated sediments in drainage channels or storm sewers. The theoretical analysis, which is based on a conventional model for the shear-induced erosion of particles from land and channel-bed surfaces, predicts that the magnitude of the exponent n reflects the geometry of the stormwater conveyance system from which the pollution derives. This raises the possibility that the scaling properties of pollutants in stormwater runoff (i.e., the value of n) may harbor information about the origin of nonpoint source pollution.

Confirmation of Escherichia coli and its distinction from Klebsiella species by gas and indole formation at 44 and 44.5 degrees C

AIMS

In the enumeration of coliform bacteria, confirmation of Escherichia coli has been based upon gas and indole production at the elevated incubation temperature. The test for gas production has recently been questioned. The aim of this study was to investigate the impact of gas production test on the reliability of confirmation of E. coli.

METHODS AND RESULTS

The impact of several media on growth, gas and/or indole formation was tested at 44 and 44.5 degrees C using 547 environmental isolates. These were mainly E. coli, Klebsiella pneumoniae, K. oxytoca and Enterobacter cloacae strains. Another set of 250 faecal and environmental klebsiellae were tested for their maximum temperature for growth (Tmax) and for gas formation. Escherichia coli and even K. pneumoniae grew well in all the media, but gas production was more dependent on the medium used. Growth of the mainly gas negative Ent. cloacae and K. oxytoca strains was still more sensitive to the medium and incubation conditions. Tryptophan salt broth was the most productive medium for the indole test, followed by lauryl tryptose mannitole and tryptone mannitol ricinoleate broth (TRM). Tmax of K. oxytoca was clearly lower than Tmax of K. pneumoniae but a rather high fraction of its isolates produced indole at 44.5 degrees C.

CONCLUSIONS

False-positive E. coli confirmation is possible if gas production is not tested for and the confirmation is based on indole test only.

SIGNIFICANCE AND IMPACT OF THE STUDY

Erroneous positive results on routine analysis for E. coli can occur.

Comparison of bacterial indicator analysis methods in stormwater-affected coastal waters

Membrane filtration (MF) and multiple tube fermentation (MTF) have been used for decades to measure indicator bacteria levels in beach water samples, but new methods based on chromogenic substrate (CS) technology are becoming increasingly popular. Only a few studies have compared results among these methods and they have generally been based on samples collected from a limited number of sites during dry weather. In this study, samples were collected from 108 sites the day after a major rainstorm, and three indicator bacteria (total coliforms (TCs), fecal coliforms (FCs) or E. coli, and enterococci (EC)) were each measured using MF, MTF, and CS. Sampling sites were selected using a stratified random design, stratified by open sandy beach, rocky shoreline, and beach areas near urban runoff outlets. The CS results were found to be highly correlated with both MF and MTF for all three indicators regardless of whether the samples were taken along open shoreline or near a runoff outlet. While correlated, TC values were higher using the CS method, consistent with other studies that have demonstrated false positives with this method. FC values were 12% lower with CS, reflecting the specificity of the CS method for E. coli rather than for the entire FC group. No significant differences were observed for EC, although some differences were observed within specific laboratories. Differences for all of these indicators were small enough that, when assessed categorically, there was more than 90% agreement between CS methods and either MF or MTF methods as to whether State of California Beach Water Quality Standards were met or exceeded.