A new membrane filtration medium for simultaneous detection and enumeration of Escherichia coli and total coliforms

A thermoelectrically stabilized aluminium acoustic trap combined with attenuated total reflection infrared spectroscopy for detection of Escherichia coli in water

Acoustic trapping is a non-contact particle manipulation method that holds great potential for performing automated assays. We demonstrate an aluminium acoustic trap in combination with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) for detection of E. coli in water. The thermal conductivity of aluminium was exploited to thermo-electrically heat and hold the acoustic trap at the desired assay temperature of 37 °C. Systematic characterisation and optimisation of the acoustic trap allowed high flow rates while maintaining high acoustic trapping performance. The ATR element serves not only as a reflector for ultrasound standing wave generation but also as a sensing interface. The enzyme conversion induced by alkaline phosphatase-labelled bacteria was directly monitored in the acoustic trap using ATR-FTIR spectroscopy. Sequential injection analysis allowed automated liquid handling, including non-contact bacteria retention, washing and enzyme-substrate exchange within the acoustic trap. The presented method was able to detect E. coli concentrations as low as 1.95 × 106 bacteria per mL in 197 min. The demonstrated ultrasound assisted assay paves the way to fully automated bacteria detection devices based on acoustic trapping combined with ATR-FTIR spectroscopy.

An inverse approach to estimate bacterial loading into an estuary by using field observations and residence time

Pathogen, whose abundance is often measured by the concentration of fecal indicator bacteria, is listed as the top cause of waterbody impairments in the US. An accurate estimation of the bacterial loading from watershed is thus fundamentally important for water quality management. Despite advances in watershed modeling, accurate estimation of bacterial load is still very challenging due to large uncertainties associated with bacterial sources, accumulation, and removal in the watershed. We introduce an inverse method using field-measured bacterial concentrations and numerical model-calculated residence time to estimate the bacterial loading from the drainage basin. In this method, an estuary is divided into multiple segments. Water and bacterial fluxes between neighboring segments are computed from a set of linear equations derived based on mass balance equation and the relationship between residence time and water fluxes. Loading to each segment can then be estimated by combining the computed water fluxes and observed bacterial concentrations. The approach accounts for seasonal and interannual variations in hydrodynamics due to tide, river discharge, and estuarine circulations. The method was applied to Nassawadox Creek, a sub-estuary of Chesapeake Bay, where Fecal Coliform concentrations at 46 stations were continuously monitored. The method is verified by the high consistency between estimated loadings and presumably known input loadings in numerical experiments with either constant or time-varying input loadings. With sparse observational data, the inversely estimated loadings agree well with the loadings from a previously calibrated watershed model, demonstrating the reliability of the method. The inverse approach can be used to cross-check the result of watershed models and assess changes in watershed condition. The method is also readily applicable to other types of materials, such as inorganic nutrients.

Elimination of total coliforms and Escherichia coli from water by means of filtration with natural clays and silica sand in developing countries

This research presents the results of a pilot system used for water treatment to be supplied to single-family or small housing nucleus at rural sector. The pilot system is constituted by an up-flow aerated filter with ceramic carrier, followed by a second down-flow filter of silica sand. The pilot plant was installed in a rural sector of the province of Loja, Ecuador, with the main purpose of monitoring the reduction in bacteria in the water for human consumption. Two natural clays from the area were tested. They were transformed into sphere-type ceramics, and then, they were placed in the pilot filters. These both natural clays are inorganic materials with high content of aluminosilicate clay minerals with favourable characteristics to achieve greater efficiency for the reduction in bacteria. The acclimatization time of 60 days allowed to achieve optimum treatment efficiency performance until 90 days of operation. The physicochemical parameters, namely temperature, pH, dissolved oxygen and total dissolved solids, were monitored throughout the experiments. Regarding microbiological parameters, up to 99% of total coliforms removal was reached for the clay called CF-CC and 79% for the other, called CF-CV. In addition, 100% of total coliforms and Escherichia Coli removal was reached for both clay systems. Social and economic viability of the proposed treatment is also analysed in the manuscript.

Evaluation of Microbiological Quality of Agricultural Water and Effect of Water Source and Holding Temperature on the Stability of Indicator Organisms' Levels by Seven U.S. Environmental Protection Agency-Approved Methods

ABSTRACT

The Food Safety Modernization Act Produce Safety Rule requires covered produce growers to monitor the quality of their agricultural water on a regular basis by some U.S. Environmental Protection Agency (EPA)-approved methods recognized by the U.S. Food and Drug Administration. In this study, we evaluated the changes in the population of indicator organisms in surface water up to 6 months, and the effects of water source and holding temperature on the survival of indicator organisms by seven EPA-approved methods (five methods for Escherichia coli and two methods for Enterococcus). The levels of E. coli and Enterococcus in the surface water were variable with sampling month, ranging from 1.61 ± 0.04 to 2.68 ± 0.15 log most probable number (MPN)/100 mL and from undetectable level to 1.19 ± 0.29 log MPN/100 mL, respectively. At 25°C (holding temperature), there were significant reductions (P < 0.05) in E. coli and Enterococcus populations in surface water after 48 and 24 h, respectively, whereas at 4°C, no significant changes in the bacterial populations were observed up to 48 h. Methods 1603, 1604, 1103.1, 10029, and Colilert showed a comparable sensitivity in quantifying E. coli, whereas method 1600 and Enterolert showed a variable sensitivity with the type of water. The results indicated that regular monitoring of agricultural water is essential to examine whether the microbial quality of water is appropriate for its intended use. Water samples should be maintained at 4°C to minimize the changes in microbial populations between sampling and testing. The comparison of the sensitivity of EPA methods for quantifying indicator organisms could provide growers with useful information for choosing the method for their water quality analysis.

HIGHLIGHTS

A Simple Off-Grid Incubator for Microbiological Water Quality Analysis

There is a need for accessible and low-cost microbiological water quality testing in contexts where diarrheal illness is a major public health concern. In most cases, the quantification of Escherichia coli and other microbial indicators by conventional culture methods requires an incubation step for processed samples at specific temperatures for bacterial growth over a prescribed time. However, incubators can be the most expensive equipment required for such microbial analyses, limiting the number and scope of water quality testing available in low-resource contexts. In this study, a low-cost incubator was developed using a locally available expanded polystyrene (EPS) foam cooler, with two water bottles filled with hot water to heat incubator to a target of 35 °C. The EPS incubator performance was validated by processing 150 water samples in duplicates using the Colilert Quanti-tray/2000 system, incubated in either the EPS incubator or a standard laboratory incubator set at 35 °C. Statistically significant correlations of results indicated that the quantification of E. coli was comparable between both methods. Risk categorizations from standard and EPS incubation results agreed for 141 of 150 (94%) samples, with zero false negatives. In addition to being reasonably mobile the EPS incubator would reduce the cost of such water quality testing, thus potentially increasing the scope of water quality testing coverage.

Water quality assessment of the ecologically stressed Hooghly River Estuary, India: A multivariate approach

Spatio-temporal and seasonal variation of the water quality characteristics of the Hooghly River Estuary, India were studied considering eight stations of diverse eco-hydrological characteristics. Wide variations in turbidity, total dissolved solids and fecal coliform exceeded the permissible BIS drinking water level limit. The estuary is observed to be relatively low-oxygenated, mesotropic and phosphate limiting. Spatial heterogeneity and impact of the southwest monsoon were remarkably pronounced in the distribution of the inorganic nutrients revealing the following values (expressed in μgatml^-1): nitrate+nitrite (2.42-37.19), phosphate (0.41-1.52) and silicate (38.5-187.75). Water Quality Index (WQI) values confirmed the prevailing 'bad' condition, detrimental for sustenance of aquatic biota. Results of Principal Component Analysis identified the major factors liable for water quality deterioration while cluster analysis categorized the stations on the basis of similar water quality status. The authors recommend adopting preventive measures for water quality improvement linked to biodiversity conservation.

Electrophoretic Concentration and Electrical Lysis of Bacteria in a Microfluidic Device Using a Nanoporous Membrane

Pathogenic bacteria such as Escherichia coli O157, Salmonella and Campylobacter are the main causes for food and waterborne illnesses. Lysis of these bacteria is an important component of the sample preparation for molecular identification of these pathogens. The pathogenicity of these bacteria is so high that they cause illness at very low concentrations (1–10 CFU/100 mL). Hence, there is a need to develop methods to collect a small number of such bacterial cells from a large sample volume and process them in an automated reagent-free manner. An electrical method to concentrate the bacteria and lyse them has been chosen here as it is reagent free and hence more conducive for online and automated sample preparation. We use commercially available nanoporous membranes sandwiched between two microfluidic channels to create thousands of parallel nanopore traps for bacteria, electrophoretically accumulate and then lyse them. The nanopores produce a high local electric field for lysis at moderate applied voltages, which could simplify instrumentation and enables lysis of the bacteria as it approaches them under an appropriate range of electric field (>1000 V/cm). Accumulation and lysis of bacteria on the nanoporous membrane is demonstrated by using the LIVE/DEAD BacLight Bacterial Viability Kit and quantified by fluorescence intensity measurements. The efficiency of the device was determined through bacterial culture of the lysate and was found to be 90% when a potential of 300 V was applied for 3 min.

A hydrogel based rapid test method for detection of Escherichia coli (E. coli) in contaminated water samples

We have formulated a new chemical composition for rapid detection ofEscherichia coli(E. coli) with currently available enzymatic substrates.

Impact of pulsed ultrasound on bacteria reduction of natural waters

There is a limited work on the use of pulsed ultrasound for water disinfection particularly the case of natural water. Hence, pulsed ultrasound disinfection of natural water was thoroughly investigated in this study along with continuous ultrasound as a standard for comparison. Total coliform measurements were applied to evaluate treatment efficiency. Factorial design of 2(3) for the tested experimental factors such as power, treatment time and operational mode was applied. Two levels of power with 40% and 70% amplitudes, treatment time of 5 and 15 min and operational modes of continuous and pulsed with On to Off ratio (R) of 0.1:0.6 s were investigated. Results showed that increasing power and treatment time or both increases total coliform reduction, whereas switching from continuous to pulsed mode in combination with power and treatment time has negative effect on total coliform reduction. A regression model for predicting total coliform reduction under different operating conditions was developed and validated. Energy and cost analyses applying electrical and calorimetric powers were conducted to serve as selection guidelines for the choosing optimum parameters of ultrasound disinfection. The outcome of these analyses indicated that low power level, short treatment time, and high R ratios are the most effective operating parameters.

The effects of precipitation, river discharge, land use and coastal circulation on water quality in coastal Maine

Faecal pollution in stormwater, wastewater and direct run-off can carry zoonotic pathogens to streams, rivers and the ocean, reduce water quality, and affect both recreational and commercial fishing areas of the coastal ocean. Typically, the closure of beaches and commercial fishing areas is governed by the testing for the presence of faecal bacteria, which requires an 18-24 h period for sample incubation. As water quality can change during this testing period, the need for accurate and timely predictions of coastal water quality has become acute. In this study, we: (i) examine the relationship between water quality, precipitation and river discharge at several locations within the Gulf of Maine, and (ii) use multiple linear regression models based on readily obtainable hydrometeorological measurements to predict water quality events at five coastal locations. Analysis of a 12 year dataset revealed that high river discharge and/or precipitation events can lead to reduced water quality; however, the use of only these two parameters to predict water quality can result in a number of errors. Analysis of a higher frequency, 2 year study using multiple linear regression models revealed that precipitation, salinity, river discharge, winds, seasonality and coastal circulation correlate with variations in water quality. Although there has been extensive development of regression models for freshwater, this is one of the first attempts to create a mechanistic model to predict water quality in coastal marine waters. Model performance is similar to that of efforts in other regions, which have incorporated models into water resource managers' decisions, indicating that the use of a mechanistic model in coastal Maine is feasible.

Physicochemical parameters aid microbial community? A case study from marine recreational beaches, Southern India

A total of 176 (water and sediment) samples from 22 stations belonging to four different (urban, semi-urban, rural, and holy places) human habitations of Tamil Nadu beaches were collected and analyzed for physiochemical and microbial parameters during 2008-2009. Bacterial counts were two- to tenfold higher in sediments than in water due to strong bacterial aggregations by dynamic flocculation and rich organic content. The elevated bacterial communities during the monsoon explain rainfalls and several other wastes from inlands. Coliform counts drastically increased at holy and urban places due to pilgrimage and other ritual activities. Higher values of the pollution index (PI) ratio (>1) reveals, human fecal pollutions affect the water quality. The averaged PI ratio shows a substantial higher microbial contamination in holy places than in urban areas and the order of decreasing PI ratios observed were: holy places > urban areas > semi-urban areas > rural areas. Correlation and factor analysis proves microbial communities were not related to physicochemical parameters. Principal component analysis indicates 55.32 % of the total variance resulted from human/animal fecal matters and sewage contaminants whereas 19.95 % were related to organic contents and waste materials from the rivers. More than 80 % of the samples showed a higher fecal coliform and Streptococci by crossing the World Health Organization's permissible limits.

Indicators of microbial beach water quality: preliminary findings from Teluk Kemang beach, Port Dickson (Malaysia)

This study aims to determine the concentrations of total coliforms and Escherichia coli (E. coli) in beach water, Teluk Kemang beach. This study was also aimed to determine relationship between total coliforms, E. coli and physicochemical parameters. As perceived health symptoms among beach visitors are rarely incorporated in beach water studies, this element was also assessed in this study. A total of eight water sampling points were selected randomly along Teluk Kemang beach. Total coliforms concentrations were found between 20 and 1940 cfu/100ml. E. coli concentrations were between 0 and 90 cfu/100ml. Significant correlations were found between total coliforms and E. coli with pH, temperature and oxidation reduction potential. Skin and eyes symptoms were the highest reported though in small numbers. Microbiological water quality in Teluk Kemang public beach was generally safe for recreational activities except sampling location near with sewage outfall.

Conservation of Dcm-mediated cytosine DNA methylation in Escherichia coli

In Escherichia coli, cytosine DNA methylation is catalyzed by the DNA cytosine methyltransferase (Dcm) protein and occurs at the second cytosine in the sequence 5'CCWGG3'. Although the presence of cytosine DNA methylation was reported over 35 years ago, the biological role of 5-methylcytosine in E. coli remains unclear. To gain insight into the role of cytosine DNA methylation in E. coli, we (1) screened the 72 strains of the ECOR collection and 90 recently isolated environmental samples for the presence of the full-length dcm gene using the polymerase chain reaction; (2) examined the same strains for the presence of 5-methylcytosine at 5'CCWGG3' sites using a restriction enzyme isoschizomer digestion assay; and (3) quantified the levels of 5-methyl-2'-deoxycytidine in selected strains using liquid chromatography tandem mass spectrometry. Dcm-mediated cytosine DNA methylation is conserved in all 162 strains examined, and the level of 5-methylcytosine ranges from 0.86% to 1.30% of the cytosines. We also demonstrate that Dcm reduces the expression of ribosomal protein genes during stationary phase, and this may explain the highly conserved nature of this DNA modification pathway.

Assessment of water quality in Asa River (Nigeria) and its indigenous Clarias gariepinus fish

Water is a valued natural resource for the existence of all living organisms. Management of the quality of this precious resource is, therefore, of special importance. In this study river water samples were collected and analysed for physicochemical and bacteriological evaluation of pollution in the Unity Road stream segment of Asa River in Ilorin, Nigeria. Juvenile samples of Clarias gariepinus fish were also collected from the experimental Asa River and from the control Asa Dam water and were analysed for comparative histological investigations and bacterial density in the liver and intestine in order to evaluate the impact of pollution on the aquatic biota. The water pH was found to range from 6.32 to 6.43 with a mean temperature range of 24.3 to 25.8 °C. Other physicochemical parameters monitored including total suspended solids, total dissolved solids, biochemical oxygen demand and chemical oxygen demand values exceeded the recommended level for surface water quality. Results of bacteriological analyses including total heterotrophic count, total coliform and thermotolerant coliform counts revealed a high level of faecal pollution of the river. Histological investigations revealed no significant alterations in tissue structure, but a notable comparative distinction of higher bacterial density in the intestine and liver tissues of Clarias gariepinus from Asa River than in those collected from the control. It was inferred that the downstream Asa River is polluted and its aquatic biota is bacteriologically contaminated and unsafe for human and animal consumption.

Seasonal variation in accurate identification of Escherichia coli within a constructed wetland receiving tertiary-treated municipal effluent

As the reuse of municipal wastewater escalates worldwide as a means to extend increasingly limited water supplies, accurate monitoring of water quality parameters, including Escherichia coli (E. coli), increases in importance. Chromogenic media are often used for detection of E. coli in environmental samples, but the presence of unique levels of organic and inorganic compounds alters reclaimed water chemistry, potentially hindering E. coli detection using enzyme-based chromogenic technology. Over seven months, we monitored E. coli levels using m-Coli Blue 24 broth in a constructed wetland filled with tertiary-treated municipal effluent. No E. coli were isolated in the wetland source waters, but E. coli, total coliforms, and heterotrophic bacteria increased dramatically within the wetland on all sampling dates, most probably due to fecal inputs from resident wildlife populations. Confirmatory testing of isolates presumptive for E. coli revealed a 41% rate of false-positive identification using m-Coli Blue 24 broth over seven months. Seasonal differences were evident, as false-positive rates averaged 35% in summer, but rose sharply to 75% in the late fall and winter. Corrected E. coli levels were significantly correlated with electrical conductivity, indicating that water chemistry may be controlling bacterial survival within the wetland. This is the first study to report that accuracy of chromogenic media for microbial enumeration in reclaimed water may show strong seasonal differences, and highlights the importance of validation of microbiological results from chromogenic media for accurate analysis of reclaimed water quality.

Molecular approach and bacterial quality of drinking water of urban and rural communities in Egypt

Water is necessary to life so when supplied as drinking water to consumers, a satisfactory quality must be maintained. In Egypt, infectious intestinal diseases are the major cause of hospitalization in almost all regions. The purpose of this study was to evaluate the microbiological quality of treated and untreated water samples from urban and rural communities. Thirty-five samples of treated (chlorinated) water from taps, 25 samples of bottled water and 15 samples of hand pump (untreated) water collected from different cities alongside the River Nile during the winter of 2007 were bacteriologically tested for safety as drinking water. This study indicated good quality of tap water and bottled water. The untreated water samples (hand pumps) were, however, slightly contaminated by faecal coliforms, faecal enterococci, Clostridium perfringens, Salmonella and Shigella. Consequently, the consumers in the villages receiving water through hand pumps are often exposed to the risk of water-borne diseases due to inadequate treatment of the raw water. Therefore, there are guidelines necessary to protect groundwater quality. Moreover, PCR-amplified by some functional gene fragments such as dctA, dcuB, frdA, dcuS and dcuR genes of the E. coli was adapted for use as a non-cultivation-based molecular approach for detection of E. coli populations from water samples without the need for pure and identified cultures.

Comparison of Escherichia coli O157:H7 enrichment in spiked produce samples

Two strains of Escherichia coli O157:H7 were spiked into six varieties of produce at approximately 0.5 CFU g(-1). Samples were enriched by using the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) method and by using an experimental method incorporating acid shock. Target colonies were detectable on selective agars after 30 of 48 analyses with BAM enrichment and 48 of 48 analyses with acid enrichment. Real-time PCR screening of 24-h enrichment broths revealed the presence of the diagnostic stx1 or stx2 genes after 27 of 48 analyses with BAM enrichment and 42 of 48 analyses with acid enrichment. The efficiency of the enrichment varied with strain and type of produce spiked but overall was better with the experimental enrichment method. Modifications of both the acid enrichment and BAM enrichment methods also were tested. The acid method with a modified incubation temperature consistently yielded high rates of recovery (> 10(8) CFU ml(-1)), with no instances in which target cells could not be detected. Modification of the BAM procedure did not reproducibly improve enrichment efficiency.

Seasonal bacteriological analysis of Gola river water contaminated with pulp paper mill waste in Uttaranchal, India

The seasonal physico-chemical and microbial quality of Gola river water has been analyzed after confluence of pulp paper mill waste. The study revealed that it has enhanced 20-30 times pollution load of BOD, COD, TDS, TSS, sulphate, chloride, sodium, nitrate, potassium, lignin and phenol after mixing of pulp paper mill waste with river water in all season. Further, it induced the bacterial growth by increasing most probable number value of E. coli was 1.57 x 10(4), 1.6 x 10(4), 1.37 x 10(4) and SPC count was 1.68 x 10(4), 1.64 x 10(4), 1.67 x 10(4)/100 ml during summer, monsoon, winter respectively. While the most probable number value in river water before mixing of pulp paper mill waste was 1.4 x 10(2), 1.82 x 10(2), 1.5 x 10(2) and SPC count was 2.8 x 10(3), 2.89 x 10(3), 2.78 x 10(3)/100 ml during summer, monsoon and winter respectively. This indicated from 88-114 fold increase in most probable number value of E. coli and 56.55-60.0 times increase in SPC count of river water after mixing of effluent in summer, monsoon and winter. Moreover, the most probable number value in effluent itself before mixing was 3.4 x 10(2), 3.3 x 10(2), 2.8 x 10(2) and SPC count was 6 x 10(4), 6.5 x 10(4), 6 x 10(4)/100 ml during summer, monsoon, winter, respectively. Furthermore, it was revealed that the seasonal variation also regulated the bacterial population dynamics as per the physico-chemical quality, in which E. coli was found highest at the rate of (5.9 x 10(4)), E. aerogenes (5.3 x 10(4)), P. aeruginosa (1.3 x 10(4)), S. aureus (3.2 x 10(3)), K. pneumoniae (2.6 x 10(4)), Enteritidis (1.1 x 10(4)) on monsoon season and V. cholerae (7.4 x 10(2)), V. vulnificus (9.2 x 10(2))/100 ml in river water when contaminated with pulp paper mill waste in monsoon season. Thus, the monsoon season showed presence of FC and TC indicated the thermo-tolerant and disease causing group of bacterial population in effluent and its sequence was observed as monsoon>summer>winter. This indicated the growth of many pathogenic and non-pathogenic bacteria for health hazards with contamination of pulp paper waste in aquatic ecosystem within the vicinity of pulp paper mill industry.

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.

Accumulation of E. Coli bacteria in mini-channel flow

The objective of this research is to design and optimize a mini/micro-channel based surface-accumulator of E. coli bacteria to be detected by acoustic wave biosensors. A computational approach has been carried out using the state of the art software, CFD-ACE with water as bacteria bearing fluid. E. coli bacteria have been modeled as random discrete particles tracked by solving the Lagrangian equations. The design challenges are to achieve low shear force (pico-N), high concentration at accumulation, and high enough Reynolds number to avoid bacteria swimming. A range of low Reynolds number (Re) has been considered along with the effects of particle boundary interactions, gravity, Saffman lift, etc. More than two orders of magnitude higher concentration at the accumulation than the inlet concentration, and lower shear force of less than pico-N have been achieved in the optimized designs.

Multiplex real-time PCR detection of heat-labile and heat-stable toxin genes in enterotoxigenic Escherichia coli

A multiplex real-time PCR method was developed for detection of heat-labile and heat-stable toxin genes in enterotoxigenic Escherichia coli. Approximately 10 CFU per reaction mixture could be detected in rinsates from produce samples. Several foods representative of varieties previously shown to have caused enterotoxigenic E. coli outbreaks were spiked and enriched for 4 or 6 h. Both heat-labile and heat-stable toxin genes could be detected in the foods tested, with the exception of hot sauce, with threshold cycle values ranging from 25.2 to 41.1. A procedure using membrane filtration which would allow enumeration of the enterotoxigenic E. coli population in a food sample in less than 28 h by real-time PCR analysis of colonies picked from media highly selective for E. coli was also developed.

Comparison of commercially available Escherichia coli enumeration tests: implications for attaining water quality standards

Many states are replacing microbiological water quality standards based on "fecal" or thermotolerant coliforms (ThCs) with new standards that employ Escherichia coli as the indicator organism. Implicit in these new standards are assumptions about the equivalence of E. coli enumeration tests and the E. coli levels that will provide protection equivalent to former ThC standards. To investigate these assumptions, E. coli levels in split samples (tests conducted on portions of the same grab sample) collected from small urban streams were determined using enzyme-specific media (Colilert, m-ColiBlue24, and nutrient agar with MUG) and compared to levels determined with conventional culture media (m-FC and m-TEC). Although levels observed with all tests were highly correlated, significantly fewer E. coli were enumerated with m-TEC than with enzyme-specific media (paired Student's t-test, alpha>99%). In addition, E. coli were found to comprise a larger fraction (84-104%, depending on the test) of the total presumptive ThC concentration than that suggested by the United States Environmental Protection Agency (63%). Both of these observations (1) the improvement in E. coli yields observed with enzyme-specific media, and (2) the greater proportion of ThC organisms that are E. coli, indicate that more water quality violations will occur when enzyme-specific media are used for testing than if conventional culture media are used.

Comparison of a new enrichment procedure for Shiga toxin-producing Escherichia coli with five standard methods

A new procedure for enrichment of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli was compared to five standard methods: the British Public Health Laboratory Service, International Standard Method, U.S. Department of Agriculture, Canadian Health Products and Food Branch, and U.S. Food and Drug Administration. The new procedure was comparable to the standard methods in its ability to detect target cells inoculated into foods at approximately 1 CFU g(-1). Comparisons were also made of the ability of the six enrichment procedures to detect E. coli O157:H7 against a large background of competitor microorganisms. In these experiments the new procedure yielded more target cells than the other five enrichments by two to three orders of magnitude as determined by enumeration on sorbitol MacConkey agar with tellurite and cefixime and Rainbow agar with tellurite and novobiocin and by verification of presumptive colonies by real-time PCR. For example, the population of enterohemorrhagic E. coli strain 6341 recovered on sorbitol MacConkey agar with tellurite and cefixime after enrichment with the experimental method was 2.42 x 10(8) CFU ml(-1) and 1.80 x 10(6) CFU ml(-1) after enrichment with the Canadian Health Products and Food Branch method, the second most effective in this experiment. In addition, broth cultures resulting from each of the six enrichment procedures were used to prepare templates for real-time PCR detection of stx1/stx2. Resulting threshold cycle (Ct) values after the experimental enrichment were similar to positive control values, whereas the five standard methods produced delayed Ct values or were not detected.

Is there an association between bacteriological drinking water quality and childhood diarrhoea in developing countries?

To investigate the association between bacteriological drinking water quality and incidence of diarrhoea, we conducted a 1-year prospective study in the southern Punjab, Pakistan. Diarrhoea episodes, drinking water sources and drinking water quality were monitored weekly among children younger than 5 years in 200 households. We found no association between the incidence of childhood diarrhoea and the number of Escherichia coli in the drinking water sources (the public domain). A possible trend was seen relating the number of E. coli in the household storage containers (the domestic domain) and diarrhoea incidence, but this did not reach statistical significance. Faecal contamination levels in household water containers were generally high even when the source water was of good quality. Under conditions such as this, it is questionable whether public water treatment will have a significant impact on the incidence of endemic childhood diarrhoea.

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.

Effect of oxygen on survival of faecal pollution indicators in drinking water

AIMS

The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water.

METHODS AND RESULTS

Aerobic and anaerobic drinking water microcosms were inoculated with E. coli ATCC 25922 or raw sewage. Survival of E. coli was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. coli in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. coli.

CONCLUSIONS

The results indicate that oxygen is a major regulator of the survival of E. coli in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. coli may persist longer in drinking water under anaerobic conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.

Improved laboratory enrichment for enterohemorrhagic Escherichia coli by exposure to extremely acidic conditions

Analysis of food samples for E. coli O157:H7 using the standard U.S. Food and Drug Administration procedure is frequently complicated by overgrowth of nontarget microorganisms. A new procedure was developed for enrichment of enterohemorrhagic E. coli (EHEC) which utilizes exposure to pH 2.00 for 2 h. This procedure yielded larger populations of EHEC than the standard method by factors ranging from 2.7 to 7.7 and, when age-stressed cultures were used, by factors ranging from 2.7 to 11.5. Cultures of competing enterics were more effectively inhibited by the new enrichment protocol as well.

Treatment of domestic wastewater by subsurface flow constructed wetlands filled with gravel and tire chip media

Subsurface flow constructed wetlands (SFCWs) are becoming increasingly common in on-site treatment of wastewater. Gravel is the most popular form of wetland fill medium, but tire chips provide more porosity, are less dense, and less expensive. This study determines the treatment efficiency of SFCWs filled with gravel or tire chip media to treat domestic wastewater. The influent and effluent of six SFCWs filled with tire chip medium and six SFCWs filled with gravel were monitored for 5 to 16 consecutive months. Parameters measured included pH, biochemical oxygen demand (BOD5), total and volatile suspended solids, NH4, P, and fecal and total coliforms. The only clear difference between medium types in wetland performance was for P. Soluble P in the effluent averaged 1.6 +/- 1.0 mg l(-1) in the tire chip-filled wetlands and 4.8 +/- 3.2 mg l(-1) in the gravel-filled wetlands. Most likely, Fe from exposed wires in shredded steel-belted tires complexed with P to create an insoluble compound. Tire chips may be a better fill medium for SFCWs than gravel because of higher porosity, lower cost, and greater reduction of P in effluent.

Ultraviolet disinfection of effluent from subsurface flow constructed wetlands

Subsurface flow constructed wetlands are becoming increasingly common for on-site treatment of domestic wastewater. Before spray application, wetland effluent must be disinfected. Traditionally, tablet chlorination has been used, but an alternative is needed to increase dependability. Consequently, we investigated the use of ultraviolet light disinfection of effluent from constructed wetlands. Two low pressure (254 nm) and two medium pressure ultraviolet bulbs (190 to 400 nm) were used for disinfection. Upon installation, all units disinfected effluent successfully. After 2 weeks in operation, three of the four units did not reduce fecal coliform populations below 200 in 100 ml of effluent due to decreased light intensity from films that developed on the bulbs. One unit consistently disinfected water to populations lower than 200 in 100 ml for 1 year without maintenance. Ultraviolet disinfection, as utilized, was not consistently suitable for disinfection of effluent from subsurface flow constructed wetlands because of coatings that developed on the bulbs and blocked the light.

Microbiological quality of drinking water of urban and rural communities, Brazil

OBJECTIVE

To evaluate the microbiological quality of treated and untreated water samples came from urban and rural communities and to examine the relationship between coliforms occurrence and average water temperature, and a comparison of the rainfall levels.

METHODS

A sample of 3,073 untreated and treated (chlorinated) water from taps (1,594), reservoir used to store treated water (1,033), spring water (96) and private well (350) collected for routine testing between 1996 and 1999 was analyzed by the multiple dilution tube methods used to detect the most probable number of total and fecal coliforms. These samples were obtained in the region of Maring , state of Paran , Brazil.

RESULTS

The highest numbers water samples contaminated by TC (83%) and FC (48%) were found in the untreated water. TC and FC in samples taken from reservoirs used to store treated water was higher than that from taps midway along distribution lines. Among the treated water samples examined, coliform bacteria were found in 171 of the 1,033 sampling reservoirs.

CONCLUSIONS

Insufficient treatment or regrowth is suggested by the observation that more than 17% of these treated potable water contained coliform. TC and FC positive samples appear to be similar and seasonally influenced in treated water. Two different periods must be considered for the occurrence of both TC and FC positive samples: (i) a warm-weather period (September-March) with high percentage of contaminated samples; and (ii) cold-weather period (April-August) were they are lower. Both TC and TF positive samples declined with the decreased of water temperature.

Effects of umbrella palms and wastewater depth on wastewater treatment in a subsurface flow constructed wetland

On-site subsurface flow constructed wetlands are designed to provide secondary quality effluent. Plants and wetland volume are considered in their design. There have been no studies, however, comparing wastewater treatment at different wastewater depths, and plant effects in wetlands are not completely understood. Investigations were conducted on these variables using four wetland cells 228 m wide by 4.75 m long containing 1 to 5 cm diameter river rock. Cyperus alternifolius (umbrella palms) were planted in one cell, and side-by-side comparisons were made between the planted and a control cell. Side-by-side comparisons were also made between cells with equal surface areas and different depths. At best umbrella palms improved effluent 5-day biochemical oxygen demand (BOD5) by 8%, suspended solids by 6%, and did not improve fecal coliform or P wastewater quality in July. When ambient air temperatures were < or = 12 degrees C during December, plants did not improve most treatment parameters. They did, however, significantly improve NH4+ treatment even when ambient air temperatures were as low as 8 degrees C. Increasing wastewater depth enhanced fecal coliform die-off but did not reduce effluent considered when maximum NH4+ reduction is a BOD5, suspended solids, NH4+, or P in effluent. Umbrella palms should be treatment goal and it is not necessary to reduce other parameters. Surface area was more important to wastewater treatment than depth.

Domestic transmission routes of pathogens: the problem of in-house contamination of drinking water during storage in developing countries

Even if drinking water of poor rural communities is obtained from a 'safe' source, it can become contaminated during storage in the house. To investigate the relative importance of this domestic domain contamination, a 5-week intervention study was conducted. Sixty-seven households in Punjab, Pakistan, were provided with new water storage containers (pitchers): 33 received a traditional wide-necked pitcher normally used in the area and the remaining 34 households received a narrow-necked water storage pitcher, preventing direct hand contact with the water. Results showed that the domestic domain contamination with indicator bacteria is important only when the water source is relatively clean, i.e. contains less than 100 Escherichia coli per 100 ml of water. When the number of E. coli in the water source is above this value, interventions to prevent the domestic contamination would have a minor impact on water quality compared with public domain interventions. Although the bacteriological water quality improved, elimination of direct hand contact with the stored water inside the household could not prevent the occasional occurrence of extreme pollution of the drinking water at its source. This shows that extreme contamination values that are often thought to originate within the domestic domain have to be attributed to the public domain transmission, i.e. filling and washing of the water pitchers. This finding has implications for interventions that aim at the elimination of these extreme contaminations.

Detection and enumeration of coliforms in drinking water: current methods and emerging approaches

The coliform group has been used extensively as an indicator of water quality and has historically led to the public health protection concept. The aim of this review is to examine methods currently in use or which can be proposed for the monitoring of coliforms in drinking water. Actually, the need for more rapid, sensitive and specific tests is essential in the water industry. Routine and widely accepted techniques are discussed, as are methods which have emerged from recent research developments.Approved traditional methods for coliform detection include the multiple-tube fermentation (MTF) technique and the membrane filter (MF) technique using different specific media and incubation conditions. These methods have limitations, however, such as duration of incubation, antagonistic organism interference, lack of specificity and poor detection of slow-growing or viable but non-culturable (VBNC) microorganisms. Nowadays, the simple and inexpensive membrane filter technique is the most widely used method for routine enumeration of coliforms in drinking water.The detection of coliforms based on specific enzymatic activity has improved the sensitivity of these methods. The enzymes beta-D galactosidase and beta-D glucuronidase are widely used for the detection and enumeration of total coliforms and Escherichia coli, respectively. Many chromogenic and fluorogenic substrates exist for the specific detection of these enzymatic activities, and various commercial tests based on these substrates are available. Numerous comparisons have shown these tests may be a suitable alternative to the classical techniques. They are, however, more expensive, and the incubation time, even though reduced, remains too long for same-day results. More sophisticated analytical tools such as solid phase cytometry can be employed to decrease the time needed for the detection of bacterial enzymatic activities, with a low detection threshold. Detection of coliforms by molecular methods is also proposed, as these methods allow for very specific and rapid detection without the need for a cultivation step. Three molecular-based methods are evaluated here: the immunological, polymerase chain reaction (PCR) and in-situ hybridization (ISH) techniques. In the immunological approach, various antibodies against coliform bacteria have been produced, but the application of this technique often showed low antibody specificity. PCR can be used to detect coliform bacteria by means of signal amplification: DNA sequence coding for the lacZ gene (beta-galactosidase gene) and the uidA gene (beta-D glucuronidase gene) has been used to detect total coliforms and E. coli, respectively. However, quantification with PCR is still lacking in precision and necessitates extensive laboratory work. The FISH technique involves the use of oligonucleotide probes to detect complementary sequences inside specific cells. Oligonucleotide probes designed specifically for regions of the 16S RNA molecules of Enterobacteriaceae can be used for microbiological quality control of drinking water samples. FISH should be an interesting viable alternative to the conventional culture methods for the detection of coliforms in drinking water, as it provides quantitative data in a fairly short period of time (6 to 8 h), but still requires research effort. This review shows that even though many innovative bacterial detection methods have been developed, few have the potential for becoming a standardized method for the detection of coliforms in drinking water samples.

A new technique for Escherichia coli testing of beef and pork carcasses

A novel technique has been developed to monitor Escherichia coli contamination on carcasses using membrane filtration and m-ColiBlue24 (mCB). mCB is a membrane filtration medium that simultaneously detects total coliforms and E. coli (EC) in a period of 24 +/- 4 h. A study was conducted, using a sponge method to obtain samples from pork carcasses and the excision technique to remove samples from beef carcasses, that compared mCB to standard methods. On pork carcasses (n = 77), the mean values for mCB and violet red bile agar were 7.4 CFU/15 cm2 and 6.1 CFU/15 cm2, respectively. The paired t test (P > 0.05) indicated no significant difference between the two methods (t = 0.5; P = 0.6). Samples from beef carcasses (n = 57) were used to compare mCB to both coliform count and EC Petrifilm. Of these samples, 27 were artificially inoculated with cattle manure. The mean total coliform count was 4.2 log CFU/cm2 and 4.0 log CFU/cm2 on mCB and coliform count Petrifilm, respectively. The mean EC count on mCB was 4.0 log CFU/cm2 and 3.5 log CFU/cm2 on EC Petrifilm. When comparing mCB to both coliform count (t = 2.4; P = 0.02) and EC (t = 3.5; P < 0.01) Petrifilm, paired t tests (P < or = 0.05) indicated significant differences.

Glutamate decarboxylase genes as a prescreening marker for detection of pathogenic Escherichia coli groups

The enzyme glutamate decarboxylase (GAD) is prevalent in Escherichia coli but few strains in the various pathogenic E. coli groups have been tested for GAD. Using PCR primers that amplify a 670-bp segment from the gadA and gadB genes encoding GAD, we examined the distribution of the gadAB genes among enteric bacteria. Analysis of 173 pathogenic E. coli strains, including 125 enterohemorrhagic E. coli isolates of the O157:H7 serotype and its phenotypic variants and 48 isolates of enteropathogenic E. coli, enterotoxigenic E. coli, enteroinvasive E. coli, and other Shiga toxin-producing E. coli (STEC) serotypes, showed that gadAB genes were present in all these strains. Among the 22 non-E. coli isolates tested, only the 6 Shigella spp. carried gadAB. Analysis of naturally contaminated water and food samples using a gadAB-specific DNA probe that was labeled with digoxigenin showed that a gadAB-based assay is as reliable as standard methods that enumerate E. coli organisms on the basis of lactose fermentation. The presence of few E. coli cells initially seeded into produce rinsates could be detected by PCR to gadA/B genes after overnight enrichment. A multiplex PCR assay using the gadAB primers in combination with primers to Shiga toxin (Stx) genes stx(1) and stx(2) was effective in detecting STEC from the enrichment medium after seeding produce rinsate samples with as few as 2 CFU. The gadAB primers may be multiplexed with primers to other trait virulence markers to specifically identify other pathogenic E. coli groups.

Specificity for field enumeration of Escherichia coli in tropical surface waters

In remote rural areas in developing countries, bacteriological monitoring often depends on the use of commercial field media. This paper evaluates a commercial field medium used for the enumeration of Escherichia coli in different surface waters under primitive field conditions in rural Pakistan. In order to verify the field kit, 117 presumptive E. coli isolates have been tested, finding a specificity of only 40%. By excluding some strains based on colony colours, the calculated specificity could be increased to 65%. Thus, it is suggested that prior to use in a tropical environment, the specificity of any commercial medium used should be tested with representative tropical isolates, in order to increase the specificity.

Rapid detection of fluorescent and chemiluminescent total coliforms and Escherichia coli on membrane filters

The detection of fluorescent colonies of Escherichia coli/total coliforms (TC) on a membrane filter is currently carried out using 4-methylumbelliferyl-beta-D-glycosides as enzyme substrates and a UV-lamp for visualization. The most rapid procedures based on this approach for the demonstration of these indicator bacteria in water take 6-7.5 h to complete. As part of efforts to further reduce the detection time, an improved two-step procedure for the fluorescence or chemiluminescence labelling of microcolonies of E. coli/TC on a membrane filter has been developed. Essential features of this approach include a separation of the bacterial propagation and target enzyme induction from the actual enzymatic labelling, the use of improved fluorogenic, i.e., 4-trifluoromethylumbelliferyl-beta-D-glycosides and fluorescein-di-beta-D-glycosides, or chemiluminogenic (i.e., phenylglucuronic- or galactose-substituted adamantyl 1,2-dioxetanes) substrates for beta-glucuronidase/beta-galactosidase, of enzyme inducers, of special membrane filters and of polymyxin B to promote the cellular uptake of the substrate. This labelling procedure has been applied in conjunction with different detection devices including a UV-lamp, CCD-cameras, X-ray film and the ChemScan((R)) RDI. Using the former three, microcolonies of pure cultures could be detected within 5.5-6.5 h, but waterborne E. coli/TC may fail to form microcolonies in this short time period, thus yielding poor sensitivity and a high false-negative rate. In contrast, a quantitative enumeration was feasible in less than 4 h with the ChemScan((R)) RDI, owing to its ability to detect both microcolonies and non-dividing single cells.

New developments in chromogenic and fluorogenic culture media

This review describes some recent developments in chromogenic and fluorogenic culture media in microbiological diagnostic. The detection of beta-D-glucuronidase (GUD) activity for enumeration of Escherichia coli is well known. E. coli O157:H7 strains are usually GUD-negative and do not ferment sorbitol. These characteristics are used in selective media for these organisms and new chromogenic media are available. Some of the new chromogenic media make the Salmonella diagnostic easier and faster. The use of chromogenic and fluorogenic substrates for detection of beta-D-glucosidase (beta-GLU) activity to differentiate enterococci has received considerable attention and new media are described. Rapid detection of Clostridium perfringens, Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus are other application of enzyme detection methods in food and water microbiology.

A 210-min solid phase cytometry test for the enumeration of Escherichia coli in drinking water

A 210-min-test for the enumeration of Escherichia coli in drinking water is described, based on solid phase cytometry (SPC) and a two-step enzymatic procedure for fluorescence labelling of single cells and small microcolonies. The test involves membrane filtration through a 25-mm black polyester filter, induction of beta-glucuronidase in the retained target cells, fluorescence labelling with fluorescein-di-beta-Dglucuronide as an enzyme substrate and laser scanning of the membrane filter. Scan results can be confirmed on-line by epifluorescence microscopy. Application to 149 naturally contaminated and uncontaminated well, tap, out-of-pump centre (distribution), surface and sewage-spiked water samples indicated > or =90% agreement and equivalence with plate count methods, including Chromocult Coliform agar and m FC agar. In 5.4% of all samples examined, SPC detected between 1 and 11 E. coli per 100 ml, while the two plate methods yielded negative results. Cases of a negative SPC result but a positive E. coli count on both reference media were not observed. This test would primarily be useful for 'emergency' monitoring of drinking water when rapid results are crucial.