Effect of ambient temperature storage on potable water coliform population estimations

The effect of the length of time between sampling potable water and performing coliform analyses has been a long-standing controversial issue in environmental microbiology. The issue is of practical importance since reducing the sample-to-analysis time may substantially increase costs for water analysis programs. Randomly selected samples (from those routinely collected throughout the State of Wisconsin) were analyzed for total coliforms after being held at room temperature (20 +/- 2 degrees C) for 24 and 48 h. Differences in results for the two holding times were compared with differences predicted by probability calculations. The study showed that storage of the potable water for up to 48 h had little effect on the public health significance of most samples containing more than two coliforms per 100 ml.     

Higher prevalence of Alternaria spp. in marine and river waters than in potable samples

Alternaria species have been recognized as important cause of allergic diseases and are considered opportunistic pathogens for immunocompromised individuals. In order to assess the contribution of waters to the spread of Alternaria, we examined 390 water samples of various origin for the presence of these microorganisms in parallel with the standard pollution indicator bacteria, i.e. total coliforms, faecal coliforms and enterococci. Alternaria spp. were isolated from 42 out of 196 (21.4%) marine water samples, from 13 out of 68 (19.1%) river samples, whereas out of 126 potable waters only two (1.6%) were found positive. The incidence of Alternaria was significantly higher (p < 0.001) in marine and river samples than in potable waters. The mean values of the colony-forming units of the pollution indicator bacteria did not significantly differ between Alternaria-positive and Alternaria-negative samples.     

Incidence of coliphage in potable water supplies.

Samples of drinking water from different sources in greater Cairo, Egypt, and bottled drinking water were tested for total coliform, fecal coliform, and coliphage populations. Of the 147 samples tested, 4 samples were positive for both total coliforms and coliphage, 65 samples were negative for total coliforms, fecal coliforms, and coliphage, and 78 samples were positive for coliphage and negative for total coliforms and fecal coliforms. The incidence of coliphage in these potable water supplies reflects the probability of human pathogenic virus survival in these waters also.     

Incidence of coliphage in potable water supplies

Samples of drinking water from different sources in greater Cairo, Egypt, and bottled drinking water were tested for total coliform, fecal coliform, and coliphage populations. Of the 147 samples tested, 4 samples were positive for both total coliforms and coliphage, 65 samples were negative for total coliforms, fecal coliforms, and coliphage, and 78 samples were positive for coliphage and negative for total coliforms and fecal coliforms. The incidence of coliphage in these potable water supplies reflects the probability of human pathogenic virus survival in these waters also.     

Failure of the most-probable-number technique to detect coliforms in drinking water and raw water supplies.

A procedure was developed to detect false-negative reactions (interference) in the standard most-probable-number (S-MPN) technique for coliform enumeration of untreated surface water and potable water supplies. This modified MPN (M-MPN) procedure allowed a quantitative assessment of the interference with coliform detection in untreated surface water and potable water supplies. Coliform interference was found to occur in the presumptive, confirmed, and completed tests of the S-MPN technique. When coliforms were present, interference with their detection occurred in over 80% of the samples. The inferior nature of the S-MPN was revealed by the 100% increase in the incidence of completed coliform-positive drinking water samples obtained with the M-MPN technique. The M-MPN procedure was also superior to the standard membrane filter technique. Eight different species of coliforms were recovered from false-negative tests, including Citrobacter, Enterobacter, Klebsiella, and Escherichia coli (in decreasing order of occurrence). The use of standard MPN techniques for monitoring potable water supplies may lead to a false security that the drinking water supply is potable, i.e., free from indicator bacteria.     

Effect of noncoliforms on coliform detection in potable groundwater: improved recovery with an anaerobic membrane filter technique

A total of 529 well and distribution potable water samples were analyzed for total coliforms by the most-probable-number and membrane filter (MF) techniques. Standard plate count bacteria and MF noncoliform bacteria were also enumerated. Frequency of coliform detection, turbidity in most-probable-number tubes, and extensive overgrowth by noncoliforms on MF filters were directly proportional to standard plate counts. Recovery of coliforms was greatest by the MF method at low (less than 100 CFU/ml) standard plate count densities and better by the most-probable-number method (confirming gas and turbid tube) at high (greater than 500 CFU/ml) standard plate count densities. In the latter case, overgrowth by noncoliforms on MF filters suppressed sheen development and, in turn, masked coliform detection. Of 341 atypical (no sheen) MF colonies verified by parallel inoculation of lauryl sulfate broth and billiant green-bile broth, 156 were aerogenic in the latter medium. Of atypical isolates, 84% were identified as either Citrobacter or Enterobacter species. A 4.3-fold reduction in numbers of overgrown MF filters and an 2.2-fold increase in numbers of coliforms recovered from 127 water samples was accomplished by anaerobic incubation of MF cultures. This anaerobic modification of the standard MF technique significantly reduced overgrowth and enhanced recovery of coliforms from potable groundwater. This technique is simple, cost effective, and suitable for monitoring of untreated ground water common to some small water systems and private water supplies.     

Effect of noncoliforms on coliform detection in potable groundwater: improved recovery with an anaerobic membrane filter technique.

A total of 529 well and distribution potable water samples were analyzed for total coliforms by the most-probable-number and membrane filter (MF) techniques. Standard plate count bacteria and MF noncoliform bacteria were also enumerated. Frequency of coliform detection, turbidity in most-probable-number tubes, and extensive overgrowth by noncoliforms on MF filters were directly proportional to standard plate counts. Recovery of coliforms was greatest by the MF method at low (less than 100 CFU/ml) standard plate count densities and better by the most-probable-number method (confirming gas and turbid tube) at high (greater than 500 CFU/ml) standard plate count densities. In the latter case, overgrowth by noncoliforms on MF filters suppressed sheen development and, in turn, masked coliform detection. Of 341 atypical (no sheen) MF colonies verified by parallel inoculation of lauryl sulfate broth and billiant green-bile broth, 156 were aerogenic in the latter medium. Of atypical isolates, 84% were identified as either Citrobacter or Enterobacter species. A 4.3-fold reduction in numbers of overgrown MF filters and an 2.2-fold increase in numbers of coliforms recovered from 127 water samples was accomplished by anaerobic incubation of MF cultures. This anaerobic modification of the standard MF technique significantly reduced overgrowth and enhanced recovery of coliforms from potable groundwater. This technique is simple, cost effective, and suitable for monitoring of untreated ground water common to some small water systems and private water supplies.     

A medium detecting β-glucuronidase for the simultaneous membrane filtration enumeration of Escherichia coli and coliforms from drinking water

A medium for the single membrane enumeration of Escherichia coli and coliforms from potable water was developed by the modification of the standard UK membrane filtration medium. The medium, membrane-Lactose Glucuronide Agar (m-LGA), employs a chromogenic substrate for the detection of β-glucuronidase activity and sodium pyruvate to enhance recovery of chlorine-stressed coliforms. Escherichia coli identification was significantly improved on m-LGA with 98.6% of presumptive isolates confirming. Recovery of coliforms from drinking water samples was also significantly improved.     

Magnitude of pollution indicator organisms in rural potable water.

A total of 460 water samples were randomly drawn from the potable water supply sources of rural communities in three counties of South Carolina. About 10% of the population, not incorporated in municipalities, was sampled. The samples were tested for total coliforms, Escherichia coli, and fecal streptococci. Significant levels of these pollution indicator organisms were detected in almost all the water supplies. Total coliforms were the most common, and only 7.5% of the water supplies were uncontaminated. E. coli, considered a reliable indicator of recent and dangerous pollution, was observed in 43% of the water supplies. Statistical analyses indicated that the bacterial populations, especially E. coli, were associated with the supply source depth and its distance from the septic tank. Total coliform counts were also weakly correlated to the pH of the water.     

Magnitude of pollution indicator organisms in rural potable water.

A total of 460 water samples were randomly drawn from the potable water supply sources of rural communities in three counties of South Carolina. About 10% of the population, not incorporated in municipalities, was sampled. The samples were tested for total coliforms, Escherichia coli, and fecal streptococci. Significant levels of these pollution indicator organisms were detected in almost all the water supplies. Total coliforms were the most common, and only 7.5% of the water supplies were uncontaminated. E. coli, considered a reliable indicator of recent and dangerous pollution, was observed in 43% of the water supplies. Statistical analyses indicated that the bacterial populations, especially E. coli, were associated with the supply source depth and its distance from the septic tank. Total coliform counts were also weakly correlated to the pH of the water.     

Molecular Method for Detection of Total Coliforms in Drinking Water Samples

This work demonstrates the ability of a bacterial concentration and recovery procedure combined with three different PCR assays targeting the lacZ, wecG, and 16S rRNA genes, respectively, to detect the presence of total coliforms in 100-ml samples of potable water (presence/absence test). PCR assays were first compared to the culture-based Colilert and MI agar methods to determine their ability to detect 147 coliform strains representing 76 species of Enterobacteriaceae encountered in fecal and environmental settings. Results showed that 86 (58.5%) and 109 (74.1%) strains yielded a positive signal with Colilert and MI agar methods, respectively, whereas the lacZ, wecG, and 16S rRNA PCR assays detected 133 (90.5%), 111 (75.5%), and 146 (99.3%) of the 147 total coliform strains tested. These assays were then assessed by testing 122 well water samples collected in the Québec City region of Canada. Results showed that 97 (79.5%) of the samples tested by culture-based methods and 95 (77.9%), 82 (67.2%), and 98 (80.3%) of samples tested using PCR-based methods contained total coliforms, respectively. Consequently, despite the high genetic variability of the total coliform group, this study demonstrated that it is possible to use molecular assays to detect total coliforms in potable water: the 16S rRNA molecular assay was shown to be as efficient as recommended culture-based methods. This assay might be used in combination with an Escherichia coli molecular assay to assess drinking water quality.     

Holding effects on coliform enumeration in drinking water samples

Standard procedures for analyzing drinking water stress the need to adhere to the time and temperature conditions recommended for holding samples collected for microbiological testing. The National Drinking Water Laboratory Certification Program requires compliance with these holding limits, but some investigators have reported difficulties in meeting them. Research was conducted by standard analytical methods to determine if changes occurred when samples were held at 5 and 22 degrees C and analyzed at 0, 24, 30, and 48 h. Samples were analyzed for coliforms by the membrane filter and fermentation-tube procedures and for heterotrophs by the pour plate method. A total of 17 treated water samples were collected from a large municipal distribution system from August to December 1981, and 12 samples were collected from January to May 1983. The samples were dosed with coliforms previously isolated from the water system, Enterobacter cloacae in 1981 and Citrobacter freundii in 1983. The coliform counts declined linearly over time, and the rates of decline were significant at both 5 and 22 degrees C. Within 24 h at 22 degrees C, levels of E. cloacae and C. freundii decreased by 47 and 26%, respectively, and at 5 degrees C, E. cloacae numbers declined by 23%. Results from these representative laboratory-grown coliforms reinforced those previously obtained with naturally occurring coliforms under the same experimental conditions. Significantly, some samples with initially unacceptable counts (greater than 4/100 ml) met the safe drinking water limits after storage at 24 h at 5 and 22 degrees C and would have been classified as satisfactory.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occurrence of microbial indicators and Clostridium perfringens in wastewater, water column samples, sediments, drinking water, and Weddell seal feces collected at McMurdo Station, Antarctica

McMurdo Station, Antarctica, has discharged untreated sewage into McMurdo Sound for decades. Previous studies delineated the impacted area, which included the drinking water intake, by using total coliform and Clostridium perfringens concentrations. The estimation of risk to humans in contact with the impacted and potable waters may be greater than presumed, as these microbial indicators may not be the most appropriate for this environment. To address these concerns, concentrations of these and additional indicators (fecal coliforms, Escherichia coli, enterococci, coliphage, and enteroviruses) in the untreated wastewater, water column, and sediments of the impacted area and drinking water treatment facility and distribution system at McMurdo Station were determined. Fecal samples from Weddell seals in this area were also collected and analyzed for indicators. All drinking water samples were negative for indicators except for a single total coliform-positive sample. Total coliforms were present in water column samples at higher concentrations than other indicators. Fecal coliform and enterococcus concentrations were similar to each other and greater than those of other indicators in sediment samples closer to the discharge site. C. perfringens concentrations were higher in sediments at greater distances from the discharge site. Seal fecal samples contained concentrations of fecal coliforms, E. coli, enterococci, and C. perfringens similar to those found in untreated sewage. All samples were negative for enteroviruses. A wastewater treatment facility at McMurdo Station has started operation, and these data provide a baseline data set for monitoring the recovery of the impacted area. The contribution of seal feces to indicator concentrations in this area should be considered.     

Evaluation of a rapid, defined substrate technology method for enumeration of total coliforms and Escherichia coli in chlorinated drinking water

A rapid, defined substrate technology method, commercially available as Colilert, simultaneously enumerates total coliforms and Escherichia coli in drinking water samples in 24 h without the need for confirmatory tests. The ability of this method to enumerate both total coliforms and E. coli in simulated chlorine-treated drinking water samples was compared with the standard UK method (minerals-modified glutamate most probable number) which requires up to 96 h to complete including confirmation. Statistical analysis by a nonparametric matched-pair test showed the Colilert method to be less efficient at detecting down to one E. coli in these samples compared to the standard UK method. No statistically significant difference between the two methods of enumeration for total coliforms was detected.     

Occurrence of Microbial Indicators and Clostridium perfringens in Wastewater, Water Column Samples, Sediments, Drinking Water, and Weddell Seal Feces Collected at McMurdo Station, Antarctica

McMurdo Station, Antarctica, has discharged untreated sewage into McMurdo Sound for decades. Previous studies delineated the impacted area, which included the drinking water intake, by using total coliform and Clostridium perfringens concentrations. The estimation of risk to humans in contact with the impacted and potable waters may be greater than presumed, as these microbial indicators may not be the most appropriate for this environment. To address these concerns, concentrations of these and additional indicators (fecal coliforms, Escherichia coli, enterococci, coliphage, and enteroviruses) in the untreated wastewater, water column, and sediments of the impacted area and drinking water treatment facility and distribution system at McMurdo Station were determined. Fecal samples from Weddell seals in this area were also collected and analyzed for indicators. All drinking water samples were negative for indicators except for a single total coliform-positive sample. Total coliforms were present in water column samples at higher concentrations than other indicators. Fecal coliform and enterococcus concentrations were similar to each other and greater than those of other indicators in sediment samples closer to the discharge site. C. perfringens concentrations were higher in sediments at greater distances from the discharge site. Seal fecal samples contained concentrations of fecal coliforms, E. coli, enterococci, and C. perfringens similar to those found in untreated sewage. All samples were negative for enteroviruses. A wastewater treatment facility at McMurdo Station has started operation, and these data provide a baseline data set for monitoring the recovery of the impacted area. The contribution of seal feces to indicator concentrations in this area should be considered.     

Comparison of the recoveries of Escherichia coli and total coliforms from drinking water by the MI agar method and the U.S. Environmental Protection Agency-approved membrane filter method.

Drinking water regulations under the Final Coliform Rule require that total coliform-positive drinking water samples be examined for the presence of Escherichia coli or fecal coliforms. The current U.S. Environmental Protection Agency-approved membrane filter (MF) method for E. coli requires two media, an MF transfer, and a total incubation time of 28 h. A newly developed MF method, the MI agar method, containing indoxyl-beta-D-glucuronide and 4-methylumbelliferyl-beta-D-galactopyranoside for the simultaneous detection of E. coli and total coliforms, respectively, by means of their specific enzyme reactions, was compared with the approved method by the use of wastewater-spiked tap water samples. Overall, weighted analysis of variance (significance level, 0.05) showed that the new medium recoveries of total coliforms and E. coli were significantly higher than those of mEndo agar and nutrient agar plus MUG (4-methylumbelliferyl-beta-D-glucuronide), respectively, and the background counts were significantly lower than those of mEndo agar (< 5%). Generally, the tap water source, overall chlorine level, wastewater source, granular activated carbon treatment of the tap water, and method of grouping data by E. coli count for statistical analysis did not affect the performance of the new medium.     

The occurrence of fungi in hospital and community potable waters

The prevalence of fungi was investigated in 126 potable water samples (84 hospital and 42 community samples), in parallel with the standard pollution indicator micro-organisms. Filamentous fungi were isolated from 104 of 126 (82.5%) samples and yeasts from 14 (11.1%), whereas their mean counts were 36.6 and 4.4, respectively. Fungi were isolated from 95.2% of community and 76.2% of hospital water samples, with the difference being statistically significant (P < 0.05), while yeasts were isolated from 9.5 and 11.9%, respectively. Prevailing genera were Penicillium spp., isolated from 64, Aspergillus spp., from 53, and Candida, from nine of the examined samples. Colony-forming units of yeasts were significantly correlated with those of total and faecal coliforms, whereas the counts of filamentous fungi were significantly correlated with total heterotrophic bacteria counts. These results suggest that tap water is a potential transmission route for fungi both in hospitals and the community in the examined region and may pose a health hazard mainly for the immunocompromised host.     

The fate of environmental coliforms in a model water distribution system

A series of experiments to determine the survival characteristics of environmental and faecal coliforms in a 1.3 km long experimental pipe distribution system is described. In the first experiments, tertiary treated effluent (10(3)-10(4) coliforms ml-1) was inoculated directly into the distribution system. Coliform organisms were not detected in any samples taken downstream of the inoculation point. By comparison, laboratory jar tests showed low level survival for coliforms at the same chloramine residuals (0.3 mg l-1) for up to 48 h. In the second series of experiments, a by-pass pipe in the experimental distribution system was isolated, drained, and filled with tertiary treated effluent (10(3)-10(4) coliforms ml-1) to simulate the conditions in a dead-end. Coliform numbers were monitored and found to decrease rapidly, but they were still detectable at low levels after 7 weeks. The water in the by-pass section was then released into the main pipe-rig and sampled downstream. No coliforms were detected in water samples or in samples swabbed from the pipe walls. Finally, the flow in the main pipe-rig and in the by-pass was increased to dislodge any deposits and biofilm into the water. The absence of coliforms in any water samples taken during or after the flow increases is contrary to the widely accepted understanding that coliforms survive and grow in biofilms on pipe walls.     

Destruction of coliforms in water and sewage water by dye-sensitized photooxidation.

A new approach to disinfection of water and sewage water, by oxidative destruction of microorganisms by photosensitization, is described. Samples of water and sewage water, to which an inoculum of fecal Escherichia coli had been added, were exposed to solar radiation in the presence of a dye sensitizer, under continuous aeration. The effects of the sensitizer methylene blue at concentrations of 0 to 10 mg/liter, different radiation times from 0 to 2 h, and sunlight intensities of 0, 68, and 2,030 muE/m2 per s were investigated. In laboratory-scale experiments, 1.3 X 10(9) coliforms in 100 ml of oxidation pond municipal sewage water containing 0.5 mg of methylene blue were destroyed in about 30 min. Similar results were obtained with nonchlorinated potable water. These results demonstrate the possibilities available for the disinfection of water and sewage water by this method.     

Destruction of coliforms in water and sewage water by dye-sensitized photooxidation.

A new approach to disinfection of water and sewage water, by oxidative destruction of microorganisms by photosensitization, is described. Samples of water and sewage water, to which an inoculum of fecal Escherichia coli had been added, were exposed to solar radiation in the presence of a dye sensitizer, under continuous aeration. The effects of the sensitizer methylene blue at concentrations of 0 to 10 mg/liter, different radiation times from 0 to 2 h, and sunlight intensities of 0, 68, and 2,030 muE/m2 per s were investigated. In laboratory-scale experiments, 1.3 X 10(9) coliforms in 100 ml of oxidation pond municipal sewage water containing 0.5 mg of methylene blue were destroyed in about 30 min. Similar results were obtained with nonchlorinated potable water. These results demonstrate the possibilities available for the disinfection of water and sewage water by this method.