F-Specific RNA Bacteriophages, Especially Members of Subgroup II, Should Be Reconsidered as Good Indicators of Viral Pollution of Oysters

Norovirus (NoV) is the leading cause of gastroenteritis outbreaks linked to oyster consumption. In this study, we investigated the potential of F-specific RNA bacteriophages (FRNAPH) as indicators of viral contamination in oysters by focusing especially on FRNAPH subgroup II (FRNAPH-II). These viral indicators have been neglected because their behavior is sometimes different from that of NoV in shellfish, especially during the depuration processes usually performed before marketing. However, a significant bias needs to be taken into account. This bias is that, in the absence of routine culture methods, NoV is targeted by genome detection, while the presence of FRNAPH is usually investigated by isolation of infectious particles. In this study, by targeting both viruses using genome detection, a significant correlation between the presence of FRNAPH-II and that of NoV in shellfish collected from various European harvesting areas impacted by fecal pollution was observed. Moreover, during their depuration, while the long period of persistence of NoV was confirmed, a similar or even longer period of persistence of the FRNAPH-II genome, which was over 30 days, was observed. Such a striking genome persistence calls into question the relevance of molecular methods for assessing viral hazards. Targeting the same virus (i.e., FRNAPH-II) by culture and genome detection in specimens from harvesting areas as well as during depuration, we concluded that the presence of genomes in shellfish does not provide any information on the presence of the corresponding infectious particles. In view of these results, infectious FRNAPH detection should be reconsidered as a valuable indicator in oysters, and its potential for use in assessing viral hazard needs to be investigated.IMPORTANCE This work brings new data about the behavior of viruses in shellfish, as well as about the relevance of molecular methods for their detection and evaluation of the viral hazard. First, a strong correlation between the presence of F-specific RNA bacteriophages of subgroup II (FRNAPH-II) and that of norovirus (NoV) in shellfish impacted by fecal contamination has been observed when both viruses are detected using molecular approaches. Second, when reverse transcription-PCR and culture are used to detect FRNAPH-II in shellfish, it appears that the genomes of the viruses present a longer period of persistence than infectious virus, and thus, virus genome detection fails to give information about the concomitant presence of infectious viruses. Finally, this study shows that FRNAPH persist at least as long as NoV does. These data are major arguments to reconsider the potential of FRNAPH as indicators of shellfish viral quality.

Seasonal gonadal development and age-related maturity patterns of introduced pumpkinseed (Lepomis gibbosus Linnaeus, 1758) in a heated thermal reservoir and an adjacent river reach

Testis and ovarian maturation status, maturity profile and gonado-somatic index (GSI) were assessed in pumpkinseed (Lepomis gibbosus) collected from Mirgenbach, a cooling-water reservoir associated with a nuclear power plant, and from the River Moselle 7km downstream of the reservoir's thermal outflow. Histological investigation indicated that in both sexes, gonadal development of pumpkinseed in the heated reservoir was more advanced than in the cooler Moselle River throughout the breeding season. The histological maturity profile of reservoir males ranked by the advancement of sperm cells was highly correlated with its GSI (rs=0.73, P<0.001). GSI of females in the reservoir increased with the stage at maturity, but GSI was not significantly correlated with total length, age or growth rate of the individual. All sampled individuals of both sexes were mature at age 1 in the heated reservoir, whereas 48% of age 1 males and 57% of age 1 females were not mature in the river. GSI patterns suggest that males in the reservoir adopted one of two reproductive strategies (nesters or cuckolders), whereas no small males with large enough testes to be considered cuckolders were apparent in the river. The warm thermal regime of Mirgenbach Reservoir led to precocial maturity, early season reproduction, and the greater prevalence of apparent cuckolder males than would normally occur in this climatic zone.

Development of a viral concentration method for bottled water stored in hydrophobic support

Several protocols have been described for the detection of genomes of enteric viruses from water using two-step procedures: membrane filtration and RT-PCR detection. However, these methods, when applied to bottled water, generally consider only the aqueous phase. Such procedures do not take into account the adhesion of viruses onto the hydrophobic container. Potential adhesion results in loss of viral concentration in the aqueous phase and consequently viral pollution is underestimated in such a system. A procedure based on the addition of surfactant to elute viruses followed by membrane concentration was developed to avoid this underestimation. Firstly, using poliovirus 1 as a model, this study demonstrated that the best solution to recover virus and/or viral genome is a mix of sodium dodecyl sulphate, a nonionic detergent and guanidine thiocyanate. Furthermore, temperature has a significant but low effect on elution. A positively charged 0.2 microm inorganic membrane composed of Alumina (Anodisc, Whatman) is also the best membrane to concentrate viral material before the detection by RT-PCR. Finally, the developed protocol gives significantly higher poliovirus 1 recovery rate than a reference protocol previously described (aqueous phase concentration on Zetapore). The difference can be explained by the recovery of the viruses adsorbed onto the water container.

Clearance of human-pathogenic viruses from sludge: study of four stabilization processes by real-time reverse transcription-PCR and cell culture

Sludges derived from wastewater treatment are foul-smelling, biologically unstable substances. As well as containing numerous pathogenic microorganisms, they also consist of organic matter that can be used as agricultural fertilizer. Legislation nevertheless requires sludges to be virologically tested prior to spreading by the counting of infectious enterovirus particles. This method, based on culture of enterovirus on BGM cells, is lengthy and not very sensitive. The aim of this study was to propose an alternative method of genome quantification for all enteroviruses that is applicable to verifying the elimination of viruses in complex samples such as sludges. Our complete protocol was compared to the official method, consisting of enterovirus enumeration with the most probable number of cythopathic unit (MPNCU) assay through the study of four stabilization procedures: liming, composting, heat treatment, and mesophile anaerobic digestion. Enterovirus quantities at the start of the stabilization procedures were between 37 and 288 MPNCU/g on the one scale and between 4 and 5 log genome copies/g on the other. It was shown that all procedures except mesophile anaerobic digestion were highly effective in the elimination of enterovirus particles and genomes in wastewater sludges. Reduction of viruses by mesophile anaerobic digestion was by only 1 log (infectious particles and genomes). In conclusion, stabilization processes can indeed be checked by virological quality control of sludges with gene amplification. However, the infectivity of genomes needs to be confirmed with cell culture or a correlation model if the virological risk inherent in the agricultural use of such sludges is to be fully addressed.

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.

Best viral elution method available for quantification of enteroviruses in sludge by both cell culture and reverse transcription-PCR

The aim of this study was to select one or several virus extraction techniques that enable simultaneous detection of enterovirus genomes and infectious particles in different types of urban sludge. Eight techniques were compared by using 16 different liquid and solid sludge samples. The numbers of infectious enteroviruses in cell cultures were determined by using the most-probable-number method. The enterovirus genome was quantified by a single-tube reverse transcription-PCR using TaqMan technology. The results were statistically analyzed by Friedman's test, a nonparametric test for analysis of randomized block data using only ranks in terms of extraction technique efficiency. Two techniques seemed to yield higher viral titers as determined by simultaneous detection by cell culture and PCR. The first involved a 10% beef extract solution at pH 9 and sonication; the second involved a 0.3 M NaCl-7% beef extract solution at pH 7.5 followed by Freon treatment. In solid sludge, no significant differences were observed among the eight techniques tested. Both of the best techniques can be used for simultaneous detection of infectious enterovirus particles and genomes in any type of urban sludge.

The glutathione-related detoxification system is increased in human breast cancer in correlation with clinical and histopathological features

PURPOSE

The glutathione detoxification pathway includes glutathione S-transferase (GST) and peroxidase (GPX) isoenzymes as well as glutathione reductase (GSSR). Though well established from cultured cancer cell lines, its involvement in resistance is still unclear in the tumours. This study aimed to describe the parameters that influence the glutathione contents and associated activities in breast cancer.

METHODS

The components of the glutathione pathway were measured in the tumours from 41 women with primary breast cancer in comparison with those in the matched tumour-free samples. Appropriate statistical studies (regression analysis, Wilcoxon signed rank test) explored the influence of clinical and prognostic factors.

RESULTS

Reduced and total glutathione contents were largely increased (P < 0.0001) and all related activities were significantly enhanced in the tumours. Interindividual variations were described, probably due to various parameters (age, menopause, axillary lymph node status, S and G2 + M cell fractions, ER, cathepsin-D and c-ErbB-2 expressions) that influence particular components of the glutathione pathway, especially the glutathione levels.

CONCLUSIONS

The breast tumours improved their redox status and detoxification capacities depending on various parameters of significance for cell proliferation and aggressiveness, which supports the involvement of the glutathione pathway in malignant cell resistance to oxidative stress and apoptosis.

The effect of liming on the microbiological quality of urban sludge

Treatments applied to sludge in order to stabilise and dehydrate them may give notable inactivation of microorganisms. This is observed when sludge is exposed either to high temperature or drastic pH when residual sludge is limed. The control of virological, parasitological and bacteriological sludge quality by detecting pathogenic microorganisms is slow and too expensive to be commonly practised. Thus, it is possible to replace pathogenic microorganisms detection by that of contamination indicators. The aim of this study was to determine the influence of liming on the behaviour of pathogenic microorganisms detected in urban sludge. The detection of Salmonella and helminth eggs was carried out in liquid sludge (2-3% dryness) and solid sludge (23% dryness) with added lime (0-45% weight/dry weight) and stored for 24 h-46 weeks. The results showed that liming modified some characteristics such as temperature, dryness and pH of the sludge. It appeared that, whatever the percentage of added lime, the temperature of liquid sludge did not change while it increased by about 9 degrees C when 30-45% lime was added to solid sludge. In the same way, the dryness of liquid sludge did not change during the liming, whereas the dryness of 45% limed solid sludge increased from 23% to 31%. Finally, 15%, 30% and 45% liming gave a pH of at least 10, 11.5 and 12, respectively, although the pH increase depended on the sludge type. The efficiency of liming was considered to be related to the pH and not to the percentage of added lime. Three factors determined the efficiency of pathogen elimination: (a) the pH reached by the sludge, (b) the period of liming activity and (c) the dryness of the sludge. Salmonella were eliminated from liquid sludge in 24 h at pH 10.7 and from solid sludge in 24 h at pH 10.0. Viable helminth egg concentration decreased to 3 eggs/10 g DM in liquid sludge in 14 d at pH 11.9 and 60 d at pH 11.6. In solid sludge, egg reduction was achieved in 24 h at pH 12.5, 7 d at pH 12.0 and 14 d at pH 11.5. From this study, it appeared that liming resulted in a much better microbiological quality of liquid sludge if its pH was maintained at 11.6 over 60 d or at pH 11.9 for 14 d. Solid sludge needed to be maintained at pH 11.5 for 14 d, pH 12.0 for 7 d or pH 12.5 for 24 h to achieve similar results.

The glutathione-related detoxification pathway in the human breast: a highly coordinated system disrupted in the tumour tissues

Glutathione and the associated enzymes, glutathione S-transferases, peroxidases, and reductase, have been implicated in cancer chemoresistance. This pathway was investigated in paired cancerous and peritumoral breast samples from 41 women. The tumours exhibited a higher redox status as deduced from increased transferase, peroxidase, and reductase activities and from higher total and reduced glutathione contents. Several components were strongly correlated in peritumoral tissues, suggesting a highly co-ordinated glutathione pathway that appeared disrupted in breast tumours with only a few correlations left. Therefore, resistance could spontaneously result from deregulated variations in the glutathione pathway, which might be relevant to the malignant disease progression.

Enterovirus genome detection in wastewater: multi centric evaluation of a commercial kit

A multi-centric study was carried out in three laboratories, to evaluate the efficiency of a standardized kit for the detection of enterovirus genome in wastewater. Twenty one samples of 20 liters of wastewater were analyzed before and after concentration through glass wool. Each sample was analyzed with the Amplicor kit as well as with techniques developed independently in each laboratory. The results show that the Amplicor kit is well suited to the detection of enterovirus genome in treated wastewater. The results may be compared to those obtained with semi-nested RT-PCR techniques used in each laboratory. However, the Amplicor kit technique is more simple and has the advantage of providing a standardized technique useful for comparative studies. During this work it was observed that the sensitivity of the detection of infectious viruses and virus genome was improved when concentrated samples were used for analysis.

Comparative study of techniques used to recover viruses from residual urban sludge

Eight virus extraction techniques were compared on three types of residual urban sludge for simultaneous detection of infectious enteroviruses, somatic coliphages, F-specific RNA bacteriophages and Bacteroides fragilis bacteriophages. The highest virus counts were found in extracts obtained using three extraction techniques described by respectively using a 10% beef extract solution at pH 9 and sonication, using a 0.3 M NaCl/7% beef extract solution at pH 7.5 and freon, and finally using a 0.1 M borate buffer/3% beef extract solution at pH 9 and sonication.

Detection of infectious enteroviruses, enterovirus genomes, somatic coliphages, and Bacteroides fragilis phages in treated wastewater

In this study, three types of treated wastewater were tested for infectious enteroviruses, the enterovirus genome, somatic coliphages, and Bacteroides fragilis phages. The aim of this work was to determine whether the presence of the two types of bacteriophages or of the enterovirus genome was a good indicator of infectious enterovirus contamination. The enterovirus genome was detected by reverse transcription-polymerase chain reaction. Infectious enteroviruses were quantified by cell culturing (BGM cells), and the bacteriophages were quantified by plaque formation on the host bacterium (Escherichia coli or B. fragilis) in agar medium. Forty-eight samples of treated wastewater were analyzed. Sixteen samples had been subjected to a secondary treatment for 8 to 12 h (A), 16 had been subjected to a secondary treatment for 30 h (B1), and 16 had been subjected to both secondary and tertiary treatments (B2). The mean concentrations of somatic coliphages were 4.9 x 10(4) PFU . liter-1 for treatment line A, 9.8 x 10(3) PFU . liter-1 for B1, and 1.4 x 10(3) PFU . liter-1 for B2, with all the samples testing positive (100%). The mean concentrations of B. fragilis phages were 1.7 x 10(3) PFU . liter-1 for A (100% positive samples), 17 to 24 PFU . liter-1 for B1 (44% positive samples), and 0.8 to 13 PFU . liter-1 for B2 (6% positive samples). The mean concentrations of infectious enteroviruses were 4 most probable number of cytopathogenic units (MPNCU) . liter-1 for A (31% positive samples) and <1 MPNCU . liter-1 for B1 and B2 (0% positive samples). The percentages of samples testing positive for the enterovirus genome were 100% for A, 56% for B1, and 19% for B2. The percentages of samples testing positive for the enterovirus genome were significantly higher than those for infectious enteroviruses. This finding may have been due to the presence of noninfectious enteroviruses or to the presence of infectious enteroviruses that do not multiply in BGM cell cultures. However, under our experimental conditions, nondetection of the genome implies the absence of infectious viruses. There was a significant correlation between the concentration of somatic coliphages or B. fragilis phages and the presence of infectious enteroviruses or the presence of the enterovirus genome. However, the somatic coliphage concentration did not lead to fluctuations in the infectious enterovirus concentration, whereas the B. fragilis phage concentration did.

Reverse transcriptase PCR detection of astrovirus, hepatitis A virus, and poliovirus in experimentally contaminated mussels: comparison of several extraction and concentration methods

Four methods of extraction and three methods of concentration of three enteric viruses from mussels were comparatively evaluated by reverse transcriptase PCR (RT-PCR). Shellfish were experimentally contaminated by immersion in seawater seeded with astrovirus, hepatitis A virus, or poliovirus. Sixty-gram samples of mussel tissues were processed by using borate buffer, glycine solution, saline beef, and saline beef-Freon extraction methods. The viruses were concentrated by precipitation with polyethylene glycol 6000 (PEG 6000) or PEG 8000 or by organic flocculation. RT-PCR was performed with RNA extracts from crude shellfish extracts and concentrates with and without Sephadex LH20 filtration. The glycine solution and borate buffer extraction methods resulted in significantly more RT-PCR-positive samples than the saline beef extraction method. We assessed the efficiency of 20 combinations of extraction and concentration methods. The borate buffer-organic flocculation, borate buffer-PEG 6000, and glycine solution-PEG 6000 combinations gave RT-PCR-positive results for all 27 samples analyzed for the three viruses. Detoxification of the samples by Sephadex LH20 filtration significantly decreased the efficiency of RT-PCR virus detection.

Alteration in methyl-methanesulfonate-induced poly(ADP-ribosyl)ation by 2-butoxyethanol in Syrian hamster embryo cells

The effects of 2-butoxyethanol (2-BE) on poly(ADP-ribosyl)ation were studied in Syrian hamster embryo (SHE) cells by measuring the cellular concentrations of the polymer poly(ADP-ribose) (pADPr) and of NAD+, the substrate of poly(ADP-ribose) polymerase (PARP). As biotransformation pathways of ethylene glycol ethers involve NAD+-dehydrogenases, it was hypothesized that 2-BE could reduce poly(ADP-ribosyl)ation by consuming NAD+. As a result DNA repair could be altered, which would explain that 2-BE had been shown to potentiate the effects of clastogenic substances such as methyl-methanesulfonate (MMS). In this study, the effects of 2-BE on MMS-induced pADPr metabolism were analyzed. The results indicated that: (i) 2-BE (5 mM) by itself did not influence significantly pADPr or NAD+ levels. (ii) 2-BE inhibited pADPr synthesis in MMS (0.2 mM)-pretreated cells, without any change in NAD+ concentrations. (iii) MMS treatment, which rapidly increased pADPr levels, also affected the poly(ADP-ribosyl)ation system as a secondary effect by damaging cell structures. Membrane permeabilization, which occurred at concentrations >1 mM MMS, led to a dramatic leakage of cellular NAD+ resulting in a strong reduction in pADPr levels. (iv) A bleomycin pulse (100 microM) applied after MMS and/or 2-BE treatment confirmed that 2-BE reduced poly(ADP-ribosyl)ation capacities of MMS-treated cells, though the glycol ether had no effect alone. This study confirmed that the inhibition of pADPr synthesis could be responsible for the synergistic effects of 2-BE with genotoxic substances. The mechanism of this inhibition cannot be explained by a lack of NAD+ at the concentrations of 2-BE tested.

Enterovirus genomes in wastewater: concentration on glass wool and glass powder and detection by RT-PCR

Standard methods for detecting enteroviruses in environmental samples require cell culture, which is time consuming and expensive. The reverse transcription-polymerase chain reaction (RT-PCR) is a rapid, sensitive method for detecting enteroviruses in water. However, environmental samples often contain substances that inhibit PCR amplification of target RNA. Hence the virus must be concentrated by procedures that do not interfere with amplification. This study shows that virus concentration by adsorption onto glass powder or glass wool supports is suitable for detecting viral genomes in treated wastewater by RT semi-nested PCR. No enterovirus genome was detected directly in 25 samples of treated wastewater by RT semi-nested PCR. However, samples concentrated by adsorption onto glass wool or glass powder showed that 48% (glass powder) and 56% (glass wool) contained virus. Secondary concentration by organic flocculation was unsuitable for detecting virus concentrated on glass wool (20% positive samples), but it helped to increase the detection of the genome after concentration on glass powder (72% positive samples).

Comparison study on three protocols used to concentrate poliovirus type 1 from drinking water

The efficiency of three techniques used to concentrate enteric viruses from water media and based on adsorption-elution on glass are tested. The techniques are adsorption on glass wool (GW) at the natural pH of the water and adsorption on glass powder using acidified water (pH 3.5). In the second case, two devices are used the classical apparatus (CGP) and the modified apparatus (MGP). A solution of glycine 0.05 M--3% beef extract pH 9.5 is used in all three techniques to perform the elution. The sensitivity of the above concentration methods is assayed with samples of 20 liters of tap water artificially contaminated with a known quantity of poliovirus type 1 (10(1) to 10(7) MPNCU [20 L]-1). The resulting concentrates are inoculated to BGM cell cultures and tittered according to the MPN technique. The study demonstrated that the recovery rate increased with the viral concentration of the samples with maximum efficiency reaching 81% for GW, 89% for CGP and 99% for MGP. A Wilcoxon test performed on paired samples and on the overall results with all three methods. Significant differences were demonstrated leading to the ranking of the techniques in the growing order of sensitivity GW, CGP and MGP. These finding were confirmed using a fitting technique according to the algorithm of Marquardt.

Bacterial inoculum density and probability of para-nitrophenol biodegradability test response

This study has been carried out to establish a model linking probability of positive response in para-nitrophenol biodegradability test to controlled variables of the test (suspended solids, SS; total bacteria, AODC; cultivable bacteria, CFU; specific biodegraders, MPN). Series of dilution of 11 raw inocula (6 activated sludges, 5 river waters) were tested. They reveal very dispersed values of biomass measured as SS, AODC, and CFU and quite comparable values of specific biodegraders for each category of inoculum (river or sludge). The proposed model fits well the empirical distribution of the experimental frequency of positive results versus inoculum density for each controlled variable. The constants k of the model, representing the fraction of biodegraders for each inoculum, were tested by the likelihood ratio test and were proven to be different from one another according to the biomass descriptor and the origin of the inoculum. The probabilistic model, in the case of para-nitrophenol biodegradation, indicates that standardized official tests (closed bottle, AFNOR, Sturm, and MITI I) are seldom optimal under those conditions. It allows the determination of which inoculum concentration can lead to a high probability (e.g., 99.9%) of observing paranitrophenol biodegradation by raw inocula.

Rotavirus quantification: a comparison between the enumerative and the MPN techniques

A commonly used technique to isolate rotaviruses from a water environment involves the inoculation on cell culture associated with the revelation of the viral multiplication by indirect immunofluorescence. The results of the experiment using this methodology may be expressed either with an enumerative technique or with a MPN technique. We have found that the enumerative method provided the highest yield as opposed to the MPN method by a ratio close to 3.7. According to the experimental conditions that were used, the enumerative method should be favored for the detection of viruses from a medium with low viral density or when quantifying viruses from a given sample. This work involves a comparative study where the MPN method is very attractive because of the ease of implementation and the rapidity with which results may be obtained.

Application of generalized linear models to the analysis of toxicity test data

Generalized linear models give a unified approach to the performance of regression analysis of dichotomous, count or continuous data. This paper studies binomial, negative binomial and gamma regression models and gives a detailed description of inference procedures based on them. In particular, the maximum likelihood procedure is described for a logistic function (binomial regression) or a log-linear regression model (negative binomial and gamma regression). The process of model fitting and evaluation is illustrated by examples referring to the determination of endpoints in acute and chronic toxicity tests.

Analysis of two-way layout of count data with negative binomial variation

A number of methods has been proposed for dealing with single-factor or factorial experiments when the requirements for performing the normal theory analysis of variance procedure are not satisfied. This paper suggests the use of the likelihood ratio statistic for testing the main effects and the interaction between the factors in two-way layout of count data following negative binomial distributions with a common dispersion parameter. The likelihood ratio statistic for testing the equality of the dispersion parameters of several groups of count data is also derived. The methods is illustrated by an example concerning the study of spatial and temporal variation of bacterial counts.

Microplate fecal coliform method to monitor stream water pollution

A study has been carried out on the Moselle River by means of a microtechnique based on the most-probable-number method for fecal coliform enumeration. This microtechnique, in which each serial dilution of a sample is inoculated into all 96 wells of a microplate, was compared with the standard membrane filter method. It showed a marked overestimation of about 14% due, probably, to the lack of absolute specificity of the method. The high precision of the microtechnique (13%, in terms of the coefficient of variation for log most probable number) and its relative independence from the influence of bacterial density allowed the use of analysis of variance to investigate the effects of spatial and temporal bacterial heterogeneity on the estimation of coliforms. Variability among replicate samples, subsamples, handling, and analytical errors were considered as the major sources of variation in bacterial titration. Variances associated with individual components of the sampling procedure were isolated, and optimal replications of each step were determined. Temporal variation was shown to be more influential than the other three components (most probable number, subsample, sample to sample), which were approximately equal in effect. However, the incidence of sample-to-sample variability (16%, in terms of the coefficient of variation for log most probable number) caused by spatial heterogeneity of bacterial populations in the Moselle River is shown and emphasized. Consequently, we recommend that replicate samples be taken on each occasion when conducting a sampling program for a stream pollution survey.