Transport of Escherichia coli in saturated porous media: dual mode deposition and intra-population heterogeneity

Because of heterogeneity among members of a bacteria population, deposition rates of bacteria may decrease upon the distance bacteria are transported in an aquifer. Such deposition rate decreases may result in retained bacteria concentrations, which decrease hyper-exponentially as a function of transport distance, and may therefore significantly affect the transport of colloids in aquifers. We investigated the occurrence of hyper-exponential deposition of Escherichia coli, an important indicator for fecal contamination, and the causes for such behavior. In a series of column experiments with glass beads of various sizes, we found that attachment of E. coli decreased hyper-exponentially, or, on logarithmic scale in a bimodal way, as a function of the transported distance from the column inlet. From data fitting of the retained bacteria concentration profiles, the sticking efficiency of 40% of the E. coli population was high (alpha=1), while the sticking efficiency of 60% was low (alpha=0.01). From the E. coli total population, an E. coli subpopulation consisting of slow attachers could be isolated by means of column passage. In subsequent column experiments this subpopulation attached less than the E. coli total population, consisting of both slow and fast attachers. We concluded that the main driver for the observed dual mode deposition was heterogeneity among members of the bacteria population. Intra-population may result in some microbes traveling surprisingly high distances in the subsurface. Extending the colloid filtration theory with intra-population variability may provide a valuable framework for assessing the transport of bacteria in aquifers.     

Confirmation of E. coli among other thermotolerant coliform bacteria in paper mill effluents, wood chips screening rejects and paper sludges

Paper sludges are solid wastes material generated from the paper production, which have been characterized for their chemical contents. Some are rich in wood fiber and are a good carbon source, for example the primary and de-inking paper sludges. Others are made rich in nitrogen and phosphorus by pressing the activated sludge, resulting from the biological water treatments, with the primary sludge, yielding the combined paper sludge. Still, in the absence of sanitary effluents very few studies have addressed the characterization of their coliform microflora. Therefore, this study investigated the thermotolerant coliform population of one paper mill effluent and two paper mill sludges and wood chips screening rejects using chromogenic media. For the first series of analyses, the medium used was Colilert broth and positive tubes were selected to isolate bacteria in pure culture on MacConkey agar. In a second series of analyses, double selective media, based on ss-galactosidase and ss-glucuronidase activities, were used to isolate bacteria. First, the presence of thermotolerant coliforms was detected in low numbers in most water effluents, but showed that the entrance of the thermotolerant coliforms was early in the industrial process. Also, large numbers of thermotolerant coliforms, i.e., 7,000,000 MPN/g sludge (dry weight; d.w.), were found in combined sludges. From this first series of isolations, bacteria were purified on MacConkey medium and identified as Citrobacter freundii, Enterobacter sp, E. sakazakii, E. cloacae, Escherichia coli, K. pneumoniae, K. pneumoniae subsp. rhinoscleromatis, K. pneumoniae subsp. ozaenae, K. pneumoniae subsp. pneumoniae, Pantoea sp, Raoultella terrigena, R. planticola. Second, the presence of thermotolerant coliforms was measured at more than 3,700-6,000 MPN/g (d.w) sludge, whereas E. coli was detected from 730 to more than 3,300 MPN/g (d.w.) sludge. The presence of thermotolerant coliform bacteria and E. coli was sometimes detected from wood chips screening rejects in large quantities. Also, indigenous E. coli were able to multiply into the combined sludge, and inoculated E. coli isolates were often able to multiply in wood chips and combined sludge media. In this second series of isolations, API20E and Biolog identified most isolates as E. coli, but others remained unidentified. The sequences of the 16S rDNA confirmed that most isolates were likely E. coli, few Burkholderia spp, but 10% of the isolates remained unidentified. This study points out that the coliform bacteria are introduced by the wood chips in the water effluents, where they can survive throught the primary clarifier and regrow in combined sludges.     

The persistence and removal of enteric pathogens in constructed wetlands

Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256log(10)day(-1) and 0.151log(10)day(-1), respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345log(10)day(-1) and 0.312log(10)day(-1), respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397log(10)day(-1) and 0.107log(10)day(-1), respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198log(10)day(-1) and 0.054log(10)day(-1), respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029log(10)day(-1) and 0.37log(10)day(-1), respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment.     

Fecal bacteria and sex hormones in soil and runoff from cropped watersheds amended with poultry litter

The application of poultry litter to agricultural fields can provide plant nutrients for crops and forage production, but fecal bacteria and the sex hormones estradiol and testosterone are components of litter that can be detrimental to the environment. Our objective was to determine if applications of poultry litter to small watersheds would contribute to the load of fecal bacteria and sex hormones to soil and runoff. We, therefore, investigated the fate and transport of fecal bacteria, estradiol and testosterone from surface applied poultry litter to four small cropped watersheds. Poultry litter was applied to meet the nitrogen requirements of pearl millet (Pennisetum glaucum L.) in 2000 and grain sorghum [Sorghum bicolor (L.) Moench] in 2001. Neither Salmonella nor Campylobacter were detected in the litter but the fecal indicator bacteria were. The average load of total coliforms, Escherichia coli, and fecal enterococci applied with the litter was 12.2, 11.9, and 12.7 log(10) cells ha(-1), respectively. The average load of estradiol and testosterone was 3.1 and 0.09 mg ha(-1), respectively. Runoff events first occurred 7 months after the first litter application in 2000, and 3 weeks after the second application in 2001. Only for the 25 July 2001 runoff event 3 weeks after the second litter application were the concentrations of total coliforms, E. coli, and fecal enterococci in runoff greater than background concentrations which were on average 5.2, 2.9, and 1.1 log(10) MPN 100 ml(-1), respectively. Average background levels of total coliforms, fecal enterococci, and E. coli in surface soil were 8.2, 7.9, and 3.5 log(10) cells kg(-1) soil. At the rate of litter application the concentrations of estradiol and testosterone in the litter did not appear to impact the background levels in the soil and runoff. Because concentrations of sex hormones in litter from other broiler operations are known to be greater than in the litter we applied, further study on the connection between concentrations of sex hormones in poultry litter and operational practices is recommended.     

The ecology of "fecal indicator" bacteria commonly found in pulp and paper mill water systems

Coliform bacteria have long been used to indicate fecal contamination of water and thus a health hazard. In this study, the in-mill water and external effluent treatment systems of seven typical Canadian pulp and paper mills were all shown to support the growth of numerous coliforms, especially Klebsiella Spp., Escherichia coli. Enterobacter spp., and Citrobacter spp. In all mills and most sampled locations, klebsiellas were the predominant coliforms. Although all but one of the mills had no sewage input and most disinfected their feed (input) water, all contained the most typical fecal indicator bacterium, E. coli. Many of the mill coliforms were classified as fecal coliforms by standard "MPN" and metabolic tests, but this was shown to be due to their thermotolerance, not their origin. Mill coliforms were shown not to be just simple transients from feedwater or furnish (wood), but to be continuously growing, especially in some of the primary clarifiers. Isolated mill coliforms grew very well on a sterilized raw combined mill effluent. The fecal streptococci (enterococci), alternative indicators of fecal health hazards, were common in all mills in the absence of sewage. Ten strains of E. coli isolated from four mills were all shown to be non-toxigenic strains of harmless serotypes. No salmonellas were found. Therefore, the use of total coliform, fecal coliform, enterococci, or E. coli counts as indicators of fecal contamination, and thus of health hazard in pulp and paper mill effluents or biosolids (sludges) known to be free of fecal input is invalid.     

Study on chlorine disinfection of pond effluent

Chlorine disinfection experiments were conducted to investigate the die-off patterns of the fecal coliforms when present in waste stabilization pond effluents containing from 100 to 400 mg l⁻¹ algae. The fecal coliform inactivation was observed to occur at two rates, i.e. an initial rapid kill followed by a slower kill. The magnitude of inactivation was found to be proportional to the initial chlorine dose and contact time and inversely proportional to the algal concentration. A mathematical model was developed to predict the fecal coliform survival ratio during the chlorination of the pond effluent. When compared with the experimental data, the predicted results had a correlation coefficient of 0.981.     

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((R)) 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((R)) 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.     

Transport of E. coli in columns of geochemically heterogeneous sediment

To elucidate the parameters determining the transport of Escherichia coli in aquifers, the attachment of E. coli in low concentrations to column sediments was investigated. The sediments comprised 0.18-0.50mm quartz sand, grains coated with goethite, calcite grains or grains of activated carbon (AC), in varying fractions (lambda=0, 0.05, 0.1, 0.2, 0.4, 0.7, 1.0) and all of similar diameter to the quartz sand. The weighted sum of favourable and unfavourable sticking efficiencies (alpha(total)) showed that upon increasing the fraction of favourable mineral grains (lambda) there was an initial rapid increase, which then slowed down. This was most pronounced in the AC experiments, followed by the calcite experiments and then the goethite experiments. We ascribe this non-linear relation to surface charge and hydrophobic heterogeneity of the E. coli population.     

Survival of infectious Poliovirus-1 in river water compared to the persistence of somatic coliphages, thermotolerant coliforms and Poliovirus-1 genome

The microbiological quality of water is currently assessed by search for fecal bacteria indicators. There is, however, a body of knowledge demonstrating that bacterial indicators are less resistant to environmental factors than human pathogenic viruses and therefore underestimate the viral risk. As river water is often used as a resource for drinking water production, it is particularly important to obtain a valid estimation of the health hazard, including specific viral risk. This work was conducted to compare the survival of infectious Poliovirus-1 used as a pathogenic virus model to the persistence of, on the one hand, thermotolerant coliforms commonly used as indicators and on the other hand, to somatic coliphages and Poliovirus-1 genome considered as potential indicators. We studied the behavior of infectious Poliovirus-1 and the three (potential) indicators of viral contamination in river water at three different temperatures (4 degrees C,18 degrees C and 25 degrees C). This experiment was performed twice with river water sampled at two different periods, once in winter and once in summer. Our results showed that the survival of thermotolerant coliforms can be 1.5-fold lower than infectious Poliovirus-1. In contrast, under all our experimental conditions, somatic coliphages and Poliovirus-1 genome persisted longer than infectious Poliovirus-1, surviving, respectively, 2-6-fold and about 2-fold longer than infectious Poliovirus-1. According to our results exclusively based on survival capacity, somatic coliphages and viral genome, unlike thermotolerant coliforms appear to be better indicators of viral contamination in river water. Moreover, the disappearance of viral genome is well-correlated to that one of infectious virus irrespective of the conditions tested.     

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.     

Survival of manure-borne E. coli in streambed sediment: Effects of temperature and sediment properties

Escherichia coli bacteria are commonly used as indicator organisms to designate of impaired surface waters and to guide the design of management practices to prevent fecal contamination of water. Stream sediments are known to serve as a reservoir and potential source of fecal bacteria (E. coli) for stream water. In agricultural watersheds, substantial numbers of E. coli may reach surface waters, and subsequently be deposited into sediments, along with fecal material in runoff from land-applied manures, grazing lands, or wildlife excreta. The objectives of this work were (a) to test the hypothesis that E. coli survival in streambed sediment in the presence of manure material will be affected by sediment texture and organic carbon content and (b) to evaluate applicability of the exponential die-off equation to the E. coli survival data in the presence of manure material. Experiments were conducted at three temperatures (4 °C, 14 °C, and 24 °C) in flow-through chambers using sediment from three locations at the Beaverdam Creek Tributary in Beltsville, Maryland mixed with dairy manure slurry in the proportion of 1000:1. Indigenous E. coli populations in sediments ranged from ca. 10¹ to 10³ MPN g⁻¹ while approx 10³ manure-borne E. coli MPN g⁻¹ were added. E. coli survived in sediments much longer than in the overlaying water. The exponential inactivation model gave an excellent approximation of data after 6-16 days from the beginning of the experiment. Slower inactivation was observed with the increase in organic carbon content in sediments with identical granulometric composition. The increase in the content of fine particles and organic carbon in sediments led not only to the slower inactivation but also to lower sensitivity of the inactivation to temperature. Streambed sediment properties have to be documented to better evaluate the role of sediments as reservoirs of E. coli that can affect microbiological stream water quality during high flow events.     

Bacterial die-off and stream transport studies

Two approaches to bacterial die-off studies are reported. In one study the tracer Serratia marcescens was released into a small stream, was recovered for 22 days and traced for a total distance of 20 km. The other study was carried out in Lake Ontario and Hamilton Bay using membrane filter chambers and E. coli, Streptococcus faecalis and Salmonella thompson. The chamber study indicated that these three organisms could survive for a minimum of 28 days and that E. coli had a much slower die-off rate than Strep. faecalis. The data imply that infrequent point discharges of fecal material may have overlapping and possible cumulative effects so that downstream or receiving waters will always contain pathogens and thus potential health hazards.     

Statistical analysis of the fluctuating counts of fecal bacteria in the water of Lake Kinneret

Counts of E. coli, Enteroccoci and fecal coliforms in four sites around Lake Kinneret (The Sea of Galilee), collected every 2-4 weeks for about 5 years during 1995-2002 showed irregular fluctuations punctuated by aperiodic outbursts of variable magnitude. Because of the haphazard nature of fecal contamination and large intervals between successive counts, these patterns were described by probabilistic models, based on the truncated Laplace or Extreme Value distribution. Their applicability was tested by comparing the predicted frequencies of counts exceeding different levels calculated from the first half of each record with those actually observed in its second half. Despite the records imperfections and minor violations of the underlying models' assumptions, there was a reasonable agreement between the estimated and actual frequencies. This demonstrated that it is possible to translate the irregular fluctuation pattern into a set of probabilities of future high counts. In principle, such probabilities can be used to quantify the water's fecal contamination pattern and as a tool to assess the efficacy of preventive measures to reduce it.     

Regrowth of coliforms and fecal coliforms in chlorinated wastewater effluent

Observations made both in the field in chlorinated effluent, and in laboratory experiments show that coliforms and fecal coliforms are capable of regrowth in chlorinated wastewater. Under field conditions regrowth of coliforms in chlorinated effluent held in a storage reservoir for about 3 days appeared inversely correlated to: (1) The residual chlorine in the storage reservoir and (2) The number of coliforms surviving chlorination. In the laboratory experiments regrowth occurred after initial doses as high as 11 ppm total chlorine even when there was no chemical inactivation of the chlorine. Fecal coliforms did not generally show regrowth to the same extent as coliforms. Regrowth occurred even when coliforms were not detectible in 10-ml of samples after chlorination.Since coliforms and fecal coliforms are capable of regrowth in chlorinated sewage effluent and admixtures of it, the sanitary significance of the number of coliforms after storage or in receiving bodies of water is difficult to interpret. Thus standards might be based on the number of coliforms, or fecal coliforms detected in effluents immediately after chlorination. However, this would not be justified if in addition to coliforms, pathogenic bacteria can regrow in chlorinated effluents.     

Fecal bacteria in the rivers of the Seine drainage network (France): sources, fate and modelling

The Seine river watershed (France) is a deeply anthropogenically impacted area, due to the high population density, intense industrial activities and intensive agriculture. The water quality and ecological functioning of the different rivers of the Seine drainage network have been extensively studied during the last fifteen years within the framework of a large French multidisciplinary scientific program (PIREN Seine program). This paper presents a synthesis of the main data gained in the scope of this program concerning the microbiological water contamination of the rivers of the Seine drainage network. The more common indicator of fecal contamination (fecal coliforms) was mainly used; some complementary works used E. coli and intestinal enterococci as alternative fecal indicators. Point sources (outfall of wastewater treatment plants) and non point sources (surface runoff and soil leaching) of fecal pollution to the rivers of the watershed were quantified. Results showed that, at the scale of a large urbanised watershed as the Seine basin, the input of fecal micro-organisms by non-point sources is much lower than the inputs by point sources. However, the local impact of diffuse non-human sources (especially surface runoff of pastured fields) can be of major importance on the microbiological quality of small headwater rivers. Fecal contamination of the main rivers of the Seine watershed (Seine, Marne, Oise rivers) was studied showing high level of microbiological pollution when compared to European guidelines for bathing waters. The strong negative impact of treated wastewater effluents outfall on the microbiological quality of receiving rivers was observed in different areas of the watershed. Once released in rivers, culturable fecal bacteria disappeared relatively rapidly due to mortality (protozoan grazing, lysis) or loss of culturability induced by stress conditions (sunlight effect, nutrient concentration, temperature). Mortality rates of E. coli were studied in different types of rivers within the watershed showing, in summer conditions, no major difference in the mortality rates in small and large rivers. As a result of these studies, a module describing the dynamics of fecal bacteria has been developed and embedded within a hydro-ecological model describing the functioning of the rivers of the whole watershed (the SENEQUE model). Once validated, such a model can be used for testing predictive scenarios and thus can be a very useful tool for the management of microbiological water quality at the scale of the whole basin.     

Reactivation and growth of non-culturable indicator bacteria in anaerobically digested biosolids after centrifuge dewatering

Recent literature has reported that high concentrations of indicator bacteria such as fecal coliforms (FCs) were measured in anaerobically digested sludges immediately after dewatering even though low concentrations were measured prior to dewatering. This research hypothesized that the indicator bacteria can enter a non-culturable state during digestion, and are reactivated during centrifuge dewatering. Reactivation is defined as restoration of culturability. To examine this hypothesis, a quantitative polymerase chain reaction (qPCR) method was developed to enumerate Escherichia coli, a member of the FC group, during different phases of digestion and dewatering. For thermophilic digestion, the density of E. coli measured by qPCR could be five orders of magnitude greater than the density measured by standard culturing methods (SCMs), which is indicative of non-culturable bacteria. For mesophilic digestion, qPCR enumerated up to about one order of magnitude more E. coli than the SCMs. After centrifuge dewatering, the non-culturable organisms could be reactivated such that they are enumerated by SCMs, and the conditions in the cake allowed rapid growth of FCs and E. coli during cake storage.     

Towards understanding inter-strain attachment variations of Escherichia coli during transport in saturated quartz sand

Although Escherichia coli is an indicator of fecal contamination in aquifers, limited research has been devoted to understanding the biological processes involved in the initial attachment of E. coli transported in abiotic porous media. The roles of the various surface structures of E. coli, like lipopolysaccharides (LPS), autotransporter proteins, and fimbriae are unknown. The objective of this research was to establish the effects of variations in surface characteristics of the outer membrane of E. coli on the attachment efficiency of 54 E. coli strains upon transport in saturated quartz sand under identical flow conditions. We used column experiments to assess retention of the E. coli strains, and we determined sphericity, motility, zeta-potential, and aggregation of all strains. LPS composition was determined based on known serotypes, and the presence/absence of 22 genes encoding surface characteristics was determined with qualitative PCR. The results indicated that under identical flow conditions, there was a variation of two orders of magnitude in the maximum breakthrough concentrations of the 54 E. coli strains. Of all factors we investigated, no single factor was able to explain attachment efficiency variations statistically significantly. However, low attachment efficiencies were associated (p = 0.13) with LPS containing saccharides with phosphate and/or carboxyl groups. These saccharide groups are acidic and likely charged with a negative O-atom, which reduced attachment to the negatively charged quartz surface. In addition, of the 22 genes tested, Afa was most associated (p = 0.21) with attachment efficiency. The work presented here bridges knowledge on colloid transport and molecular microbiology, and tries to offer a more holistic view on the attachment of planktonic E. coli bacteria to (abiotic) quartz grain surfaces. Future research should involve the use of microbiological techniques in order to be able to map the unique or grouped characteristics of E. coli in aquifers, and to assess the usefulness of E. coli as a fecal indicator in aquifers.     

Pilot-plant comparative study of peracetic acid and sodium hypochlorite wastewater disinfection

Peracetic acid (PAA) use in wastewater disinfection was assessed by examining its performances in a pilot plant fed by the effluent from a conventional activated-sludge treatment plant. The influence of PAA initial concentrations (0.5-4.0 mg/l) and contact times (8-38 min) on the presence of seven microorganisms (total coliforms, fecal coliforms, fecal streptococci, Escherichia coli, Pseudomonas sp., Salmonella sp., and bacteriophages anti-E. coli) and on residual biocide and halogenated organic compound (AOXs) concentrations were evaluated. The data so obtained were compared to the corresponding results acquired using sodium hypochlorite (HYP) in the same experimental conditions. The biocide effect of PAA against total and fecal coliforms, E. coli, Pseudomonas sp. and Salmonella sp. was similar to that shown by HYP. The former disinfectant was, however, less efficient than the latter in the reduction of fecal streptococci and bacteriophages anti-E. coli. In both cases the biocide quantities initially introduced in the sewage resulted in the presence of significant concentrations at the end of the contact time. No significant variation of AOX content was detected in the effluent treated with PAA, whereas a progressive increment of such compounds was found when increasing quantities of HYP were added to the sewage.     

In situ measurement and statistical modelling of Escherichia coli decay in small rivers

Numerous studies have been carried out on the environmental factors associated with the decay of faecal bacteria in open (fresh or marine) waters. The present study aimed at understanding the fate of bacteria in small streams (flow <20 m3 s(-1)) for which there is a lack of knowledge. An original in situ protocol was developed for measuring the die-off of Escherichia coli (E. coli) from wastewater treatment plants. Based upon 80 values of the decay first-order parameter (K or its inverse T90), collected from five rivers in Normandy (France), a median T90 of 10 h and a minimal T90 of 1.3 h were obtained. K was then modelled as a linear function of variables made up from flow, water temperature and suspended particulate matter (SPM). The set of significant co-variables did not include light indicators. E. coli decay is inversely related to the river flow and it becomes highly significant below 0.3 m3 s(-1). The positive effect of small flows on die-off is increased by water temperature over 15 degrees C, whereas it could be reduced by SPM. The major co-variable of the model (p < 10(-9)) is an empiric composite variable integrating the effect of flow and temperature that explains more than 40% of the variance of K. We interpreted this as an expression of predation by benthic micro-grazers which could be the main cause of E. coli die-off in small streams in temperate countries.     

Fates of bacteriophages and bacterial indicators in the Moselle river (France)

It has been suggested that bacteriophages can provide useful information about the pathogenic microorganisms, particularly enteric viruses, present in water. This information is complementary to that obtained from bacterial indicators of faecal contamination, which would be of great value for evaluating the risks associated with the use of certain types of water. Before bacteriophages can be used as indicators of faecal contamination, we need to confirm that bacteriophages give a different response to that given by the well-known bacteria indicators and to determine what happens to bacteriophages in river water. Indeed, drinking water is often produced from river water, either by natural filtration through the soil or after undergoing various treatments. We collected 96 river water samples from six different sites between February and November 2000. The samples were analysed for three faecal indicator bacteria (thermotolerant coliforms, enterococci and spores of sulphite-reducing anaerobes) and three types of bacteriophages (somatic coliphages, F-specific phages and Bacteroides fragilis phages). The densities of thermotolerant coliforms and enterococci depended mainly on physical factors such as flow rate and water temperature. High temperature and low flow rate led to a decrease in the density of these microorganisms, especially in the absence of a major input of faecal pollution. Conversely, the densities of somatic coliphages, F-specific phages and spores of sulphite-reducing anaerobes remained constant regardless of the flow rate and temperature. The density of Bacteroides fragilis phages was too low for unambiguous determination of their fate in river water.