The Diversity of Coliphages and Coliforms in Horse Feces Reveals a Complex Pattern of Ecological Interactions

The diversity of coliphages and indigenous coliform strains (ICSs) simultaneously present in horse feces was investigated by culture-based and molecular methods. The richness of coliforms (as estimated by the Chao1 method) is about 1,000 individual ICSs distinguishable by genomic fingerprinting present in a single sample of feces. This unexpectedly high value indicates that some factor limits the competition of coliform bacteria in the horse gut microbial system. In contrast, the diversity of phages active against any selected ICS is generally limited to one to three viral genotypes present in the sample. The sensitivities of different ICSs to simultaneously present coliphages overlap only slightly; the phages isolated from the same sample on different ICSs are usually unrelated. As a result, the titers of phages in fecal extract as determined for different Escherichia coli strains and ICSs may differ by several orders of magnitude. Summarizing all the data, we propose that coliphage infection may provide a selection pressure that maintains the high level of coliform diversity, restricting the possibility of a few best competitors outgrowing other ICSs. We also observed high-magnitude temporal variations of coliphage titers as determined using an E. coli C600 test culture in the same animal during a 16-day period of monitoring. No correlation with total coliform count was observed. These results are in good agreement with our hypothesis.     

Synthesis of Indicator Strains and Density of Ribonucleic Acid-Containing Coliphages in Sewage

Escherichia coli strains freshly isolated from natural sources are inefficient indicators of coliphages present in sewage. Four E. coli strains recently isolated from clinical specimens were mutagenized to obtain lac(-) mutants. Such mutants were infected with an F'lac(+) sex factor of E. coli K-12. Pairs of isogenic lac(-) and lac(-)/F'lac(+) strains were used as indicators of coliphages present in sewage, and it was found that such strains can be effectively used for a direct and almost selective enumeration of F-specific coliphage contents of sewage samples. Serological tests were applied to a number of F-specific phages isolated. All the isolates that were tested fell into two distinguishable antigenic classes: members of one class being related to ribonucleic acid (RNA) phage MS2 and those of the other being related to another RNA phage, namely, Qbeta. MS2-related phages have been found to be more widely distributed than the Qbeta related phages. Most habitats sampled were found to yield only one or the other kind of phage. Single-stranded deoxyribonucleic acid-containing F-specific phages were not detectable by the methods employed by us.     

F+ RNA coliphage typing for microbial source tracking in surface waters

AIMS: The utility of coliphages to detect and track faecal pollution was evaluated using South Carolina surface waters that exceeded State faecal coliform standards. METHODS AND RESULTS: Coliphages were isolated from 117 surface water samples by single agar layer (SAL) and enrichment presence/absence (EP/A) methods. Confirmed F+ RNA coliphages were typed for microbial source tracking using a library-independent approach. Concentrations of somatic coliphages using 37 and 44.5 degrees C incubation temperatures were found to be significantly different and the higher temperature may be more specific for faecal contamination. The EP/A technique detected coliphages infecting Escherichia coli Famp in 38 (66%) of the 58 surface water samples negative for F+ coliphages by the SAL method. However, coliphages isolated by EP/A were found to be less representative of coliphage diversity within a sample. Among the 2939 coliphage isolates tested from surface water and known source samples, 813 (28%) were found to be F+ RNA. The majority (94%) of surface water F+ RNA coliphage isolates typed as group I. Group II and/or III viruses were identified from 14 surface water stations, the majority of which were downstream of wastewater discharges. These sites were likely contaminated by human-source faecal pollution. CONCLUSIONS: The results suggest that faecal contamination in surface waters can be detected and source identifications aided by coliphage analyses. SIGNIFICANCE AND IMPACT OF THE STUDY: This study supports the premise that coliphage typing can provide useful, but not absolute, information to distinguish human from animal sources of faecal pollution. Furthermore, the comparison of coliphage isolation methods detailed in this study should provide valuable information to those wishing to incorporate coliphage detection into water quality assessments.     

Temperate coliphages: classification and correlation with habitats

Temperate coliphages were recovered from sewage, mammalian feces, and lysogenic strains of Escherichia coli. A total of 32 phages of independent origin were divided into six groups by applying the criteria of host range, antigenic homology, and the ultraviolet inducibility of the prophage. The demonstration of genetic interactions in some cases has confirmed the classification scheme. Nine phages were assigned to the P2 family and 19 to the lambda family. The remaining four isolates may represent some novel phylogenetic types. Phages recovered from the lysogenic strains of E. coli were all found to be P2 related, whereas a majority of the phages recovered as cell-free plaque-forming units were assignable to the lambda family. It is proposed that the biological attributes of the phages belonging to the two principal families are reflected in the distribution patterns observed. The virions of phage HK256 show multiple tail fibers and may thus represent a "new" virion form among the temperate coliphages.     

Evaluation of F+ RNA and DNA coliphages as source-specific indicators of fecal contamination in surface waters

Male-specific (F+) coliphages have been investigated as viral indicators of fecal contamination that may provide source-specific information for impacted environmental waters. This study examined the presence and proportions of the different subgroups of F+ coliphages in a variety of fecal wastes and surface waters with well-defined potential waste impacts. Municipal wastewater samples had high proportions of F+ DNA and group II and III F+ RNA coliphages. Bovine wastewaters also contained a high proportion of F+ DNA coliphages, but group I and IV F+ RNA coliphages predominated. Swine wastewaters contained approximately equal proportions of F+ DNA and RNA coliphages, and group I and III F+ RNA coliphages were most common. Waterfowl (gull and goose) feces contained almost exclusively F+ RNA coliphages of groups I and IV. No F+ coliphages were isolated from the feces of the other species examined. F+ coliphage recovery from surface waters was influenced by precipitation events and animal or human land use. There were no significant differences in coliphage density among land use categories. Significant seasonal variation was observed in the proportions of F+ DNA and RNA coliphages. Group I F+ RNA coliphages were the vast majority (90%) of those recovered from surface waters. The percentage of group I F+ RNA coliphages detected was greatest at background sites, and the percentage of group II F+ RNA coliphages was highest at human-impacted sites. Monitoring of F+ coliphage groups can indicate the presence and major sources of microbial inputs to surface waters, but environmental effects on the relative occurrence of different groups need to be considered.     

Pretreatment to reduce somatic salmonella phage interference with FRNA coliphage assays: successful use in a one-year survey of vulnerable groundwaters

Somatic salmonella (SS) phages were commonly found in higher numbers than F-specific RNA (FRNA) coliphages in a multi-site survey of contamination-vulnerable groundwaters. The relative abundance of SS phages required that a pretreatment procedure be implemented to reduce the SS phage content of samples before FRNA coliphage assay with Salmonella typhimurium WG49. Pretreatment involved selective SS phage removal by Salm. typhimurium WG45 cells. This pretreatment proved effective in producing interference-free samples throughout the one-year survey period and in seeded evaluation, was shown not to affect the detection of representative FRNA coliphage MS2. During the survey, 30 groundwater sites located in the continental United States, Puerto Rico and the Virgin Islands were examined for FRNA coliphages and SS phages at monthly intervals. FRNA coliphages were detected at six of the 30 sites and in 33 of 329 monthly samples. SS phages were also detected at six sites and in 28 of 329 monthly samples. Five of the phage-positive sites were positive for both phage groups. At those five sites, 58 monthly samples were collected during the survey period. Those 58 samples yielded an average FRNA coliphage concentration of 140 pfu per 100 1 of groundwater as compared to an average SS phage concentration of 565 pfu per 100 1 of groundwater. Twenty of the 58 samples were positive for both FRNA coliphages and SS phages. In those samples, FRNA coliphages were more abundant in five samples; SS phages were more abundant in 15 samples. Because these results demonstrate that SS phage levels may often exceed FRNA coliphage levels in environmental waters, it is clear that SS phage removal procedures will greatly enhance the effectiveness of the WG49-based FRNA coliphage assay.     

Ecology of coliphages in southern California coastal waters

Aims: This study aims to investigate the ecology of coliphages, an important microbial pollution indicator. Specifically, our experiments address (i) the ability of environmental Escherichia coli (E. coli) to serve as hosts for coliphage replication, and (ii) the temporal and spatial distribution of coliphages in coastal waters. Methods and Results: Water samples from three locations in California’s Newport Bay watershed were tested for the presence of coliphages every 2 weeks for an entire year. A total of nine E. coli strains isolated from various sources served as hosts for coliphage detection. Coliphage occurrence was significantly different between freshwater, estuarine and coastal locations and correlated with water temperature, salinity and rainfall in the watershed. The coliphages isolated on the environmental hosts had a broad host‐range relative to the coliphages isolated on an E. coli strain from sewage and a US EPA recommended strain for coliphage detection. Conclusions: Coliphage occurrence was related to the temperature, rainfall and salinity within the bay. The adaptation to a broad host‐range may enable the proliferation of coliphages in the aquatic environment. Significance and Impact of the Study: Understanding the seasonal variation of phages is useful for establishing a background level of coliphage presence in coastal waters. The broad host‐range of coliphages isolated on the environmental E. coli host calls for investigation of coliphage replication in the aquatic environment.     

Studies on bacteriophage distribution: virulent and temperate bacteriophage content of mammalian feces.

Freshly voided samples of the feces of cows, pigs, and humans were analyzed for the enumeration of cell-free plaque-forming units (PFU) of coliphages and Salmonella phages. Coliphage PFU counts per gram (wet weight) of feces were found to range from less than 10(1) to greater than 10(7). Salmonella phages were found in three out of five porcine samples, but none were found in the four bovine samples analyzed. Virulent coliphages related to the phiX174/S13 serological group showed some "habitat preference" in that the S13 type of phages was found only in pig feces, whereas the phiX174 type of phages was found only in cow dung. Temperate coliphages were detectable in a majority of samples of both human and porcine origin but were infrequently found in bovine samples. About 80% of the temperate coliphages of fecal origin have been found to be serologically related to phage HK022 (Dhillon and Dhillon, 1973), and all are efficiently inducible by ultraviolet light irradiation. However, considerable diversity with the group was found when the prophage immunity pattern of 10 randomly selected isolates was examined.     

Sequence variation among group III F-specific RNA coliphages from water samples and swine lagoons

Typing of F-specific RNA (FRNA) coliphages has been proposed as a useful method for distinguishing human from animal fecal contamination in environmental samples. Group II and III FRNA coliphages are generally associated with human wastes, but several exceptions have been noted. In the present study, we have genotyped and partially sequenced group III FRNA coliphage field isolates from swine lagoons in North Carolina (NC) and South Carolina (SC), along with isolates from surface waters and municipal wastewaters. Phylogenetic analysis of a region of the 5' end of the maturation protein gene revealed two genetically different group III FRNA subclusters with 36.6% sequence variation. The SC swine lagoon isolates were more closely related to group III prototype virus M11, whereas the isolates from a swine lagoon in NC, surface waters, and wastewaters grouped with prototype virus Q-beta. These results suggest that refining phage genotyping systems to discriminate M11-like phages from Q-beta-like phages would not necessarily provide greater discriminatory power in distinguishing human from animal sources of pollution. Within the group III subclusters, nucleotide sequence diversity ranged from 0% to 6.9% for M11-like strains and from 0% to 8.7% for Q-beta-like strains. It is demonstrated here that nucleotide sequencing of closely related FRNA strains can be used to help track sources of contamination in surface waters. A similar use of phage genomic sequence information to track fecal pollution promises more reliable results than phage typing by nucleic acid hybridization and may hold more potential for field applications.     

Evaluation of F+ RNA and DNA Coliphages as Source-Specific Indicators of Fecal Contamination in Surface Waters

Male-specific (F+) coliphages have been investigated as viral indicators of fecal contamination that may provide source-specific information for impacted environmental waters. This study examined the presence and proportions of the different subgroups of F+ coliphages in a variety of fecal wastes and surface waters with well-defined potential waste impacts. Municipal wastewater samples had high proportions of F+ DNA and group II and III F+ RNA coliphages. Bovine wastewaters also contained a high proportion of F+ DNA coliphages, but group I and IV F+ RNA coliphages predominated. Swine wastewaters contained approximately equal proportions of F+ DNA and RNA coliphages, and group I and III F+ RNA coliphages were most common. Waterfowl (gull and goose) feces contained almost exclusively F+ RNA coliphages of groups I and IV. No F+ coliphages were isolated from the feces of the other species examined. F+ coliphage recovery from surface waters was influenced by precipitation events and animal or human land use. There were no significant differences in coliphage density among land use categories. Significant seasonal variation was observed in the proportions of F+ DNA and RNA coliphages. Group I F+ RNA coliphages were the vast majority (90%) of those recovered from surface waters. The percentage of group I F+ RNA coliphages detected was greatest at background sites, and the percentage of group II F+ RNA coliphages was highest at human-impacted sites. Monitoring of F+ coliphage groups can indicate the presence and major sources of microbial inputs to surface waters, but environmental effects on the relative occurrence of different groups need to be considered.     

Sunlight inactivation of fecal indicator bacteria and bacteriophages from waste stabilization pond effluent in fresh and saline waters

Sunlight inactivation in fresh (river) water of fecal coliforms, enterococci, Escherichia coli, somatic coliphages, and F-RNA phages from waste stabilization pond (WSP) effluent was compared. Ten experiments were conducted outdoors in 300-liter chambers, held at 14C (mean river water temperature). Sunlight inactivation (k(S)) rates, as a function of cumulative global solar radiation (insolation), were all more than 10 times higher than the corresponding dark inactivation (k(D)) rates in enclosed (control) chambers. The overall k(S) ranking (from greatest to least inactivation) was as follows: enterococci > fecal coliforms greater-than-or-equal E. coli > somatic coliphages > F-RNA phages. In winter, fecal coliform and enterococci inactivation rates were similar but, in summer, enterococci were inactivated far more rapidly. In four experiments that included freshwater-raw sewage mixtures, enterococci survived longer than fecal coliforms (a pattern opposite to that observed with the WSP effluent), but there was little difference in phage inactivation between effluents. In two experiments which included simulated estuarine water and seawater, sunlight inactivation of all of the indicators increased with increasing salinity. Inactivation rates in freshwater, as seen under different optical filters, decreased with the increase in the spectral cutoff (50% light transmission) wavelength. The enterococci and F-RNA phages were inactivated by a wide range of wavelengths, suggesting photooxidative damage. Inactivation of fecal coliforms and somatic coliphages was mainly by shorter (UV-B) wavelengths, a result consistent with photobiological damage. Fecal coliform repair mechanisms appear to be activated in WSPs, and the surviving cells exhibit greater sunlight resistance in natural waters than those from raw sewage. In contrast, enterococci appear to suffer photooxidative damage in WSPs, rendering them susceptible to further photooxidative damage after discharge. This suggests that they are unsuitable as indicators of WSP effluent discharges to natural waters. Although somatic coliphages are more sunlight resistant than the other indicators in seawater, F-RNA phages are the most resistant in freshwater, where they may thus better represent enteric virus survival.     

Sequence Variation among Group III F-Specific RNA Coliphages from Water Samples and Swine Lagoons

Typing of F-specific RNA (FRNA) coliphages has been proposed as a useful method for distinguishing human from animal fecal contamination in environmental samples. Group II and III FRNA coliphages are generally associated with human wastes, but several exceptions have been noted. In the present study, we have genotyped and partially sequenced group III FRNA coliphage field isolates from swine lagoons in North Carolina (NC) and South Carolina (SC), along with isolates from surface waters and municipal wastewaters. Phylogenetic analysis of a region of the 5′ end of the maturation protein gene revealed two genetically different group III FRNA subclusters with 36.6% sequence variation. The SC swine lagoon isolates were more closely related to group III prototype virus M11, whereas the isolates from a swine lagoon in NC, surface waters, and wastewaters grouped with prototype virus Q-beta. These results suggest that refining phage genotyping systems to discriminate M11-like phages from Q-beta-like phages would not necessarily provide greater discriminatory power in distinguishing human from animal sources of pollution. Within the group III subclusters, nucleotide sequence diversity ranged from 0% to 6.9% for M11-like strains and from 0% to 8.7% for Q-beta-like strains. It is demonstrated here that nucleotide sequencing of closely related FRNA strains can be used to help track sources of contamination in surface waters. A similar use of phage genomic sequence information to track fecal pollution promises more reliable results than phage typing by nucleic acid hybridization and may hold more potential for field applications.     

Survival of F-specific RNA coliphage,feline calicivirus,and Escherichia coli in water: a comparative study

The relationship between the survival of enteric viral pathogens and their indicators (coliform bacteria and coliphages) is not well understood. We compared the survival rates of feline calicivirus (FCV), Escherichia coli, and a male-specific RNA coliphage MS2 at 4, 25, and 37 degrees C for up to 28 days in dechlorinated water. The survival rates of E. coli and FCV, a surrogate of noroviruses (NV), had a high degree of correlation at 4 and 25 degrees C, while MS2 phage survived significantly longer (P < 0.05) at these two temperatures. At 37 degrees C, the survival rates for all three organisms were highly correlated. Decimal reduction values indicating the number of days needed for 90% reduction in titer (D values) decreased for all three organisms as storage temperatures increased. FCV had the shortest D value among all three organisms at all temperatures investigated. These findings indicate that F-specific RNA phages may be useful indicators of NV in the environment.     

Propagation of ribonucleic acid coliphages in gnotobiotic mice.

To clarify the propagation cycle of bacteriophages in their natural habitats, we tested whether animals could support ribonucleic acid (RNA) phage propagation in their intestines, using germfree mice as the test animal. Propagation of four different antigenic types of RNA phages was tested. No detectable propagation or colonization of RNA phages was observed either in germfree mice or in gnotobiotic mice infected with the F- strain of Escherichia coli. Propagation or colonization was observed when RNA phages were orally introduced into gnotobiotic mice harboring the F+ or F' strain of E. coli. These results were consistent with data for in vitro propagation experiments. Fecal titers of phages were monitored over 24 to 98 days and were found to vary from 10(5) to 10(11) plaque-forming units per g of feces. Streptomycin administration gradually led to the disappearance of bacteria and, concomitantly, the RNA phages. Phages recovered from gnotobiotic mice feces included some of novel antigenic types. The bacterial isolates recovered from gnotobiotic mice harboring F+ bacteria included the original F+ strain, strains which had become F-, and some which had become inefficient hosts for the propagation of RNA phages.     

Propagation of ribonucleic acid coliphages in gnotobiotic mice.

To clarify the propagation cycle of bacteriophages in their natural habitats, we tested whether animals could support ribonucleic acid (RNA) phage propagation in their intestines, using germfree mice as the test animal. Propagation of four different antigenic types of RNA phages was tested. No detectable propagation or colonization of RNA phages was observed either in germfree mice or in gnotobiotic mice infected with the F- strain of Escherichia coli. Propagation or colonization was observed when RNA phages were orally introduced into gnotobiotic mice harboring the F+ or F' strain of E. coli. These results were consistent with data for in vitro propagation experiments. Fecal titers of phages were monitored over 24 to 98 days and were found to vary from 10(5) to 10(11) plaque-forming units per g of feces. Streptomycin administration gradually led to the disappearance of bacteria and, concomitantly, the RNA phages. Phages recovered from gnotobiotic mice feces included some of novel antigenic types. The bacterial isolates recovered from gnotobiotic mice harboring F+ bacteria included the original F+ strain, strains which had become F-, and some which had become inefficient hosts for the propagation of RNA phages.     

Male-specific coliphages as indicators of thermal inactivation of pathogens in biosolids

Male-specific (F+) coliphages have been proposed as a candidate indicator of fecal contamination and of virus reduction in waste treatment. However, in this and earlier work with a laboratory thermophilic anaerobic digester, a heat-resistant fraction of F+ coliphage populations indigenous to municipal wastewater and sludge was evident. We therefore isolated coliphages from municipal wastewater sludge and from biosolid samples after thermophilic anaerobic digestion to evaluate the susceptibility of specific groups to thermal inactivation. Similar numbers of F+ DNA and F+ RNA coliphages were found in untreated sludge, but the majority of isolates in digested biosolids were group I F+ RNA phages. Separate experiments on individual isolates at 53 degrees C confirmed the apparent heat resistance of group I F+ RNA coliphages as well as the susceptibility of group III F+ RNA coliphages. Although few F+ DNA coliphages were recovered from the treated biosolid samples, thermal inactivation experiments indicated heat resistance similar to that of group I F+ RNA phages. Hence, F+ DNA coliphage reductions during thermophilic anaerobic digestion are probably related to mechanisms other than thermal inactivation. Further studies should focus on the group III F+ RNA coliphages as potential indicators of reductions of heat-resistant pathogens in thermal processes for sludge treatment.     

The passage and propagation of fecal indicator phages in birds

The presence of F-specific phages in the diet of birds influenced the presence of these fecal indicators in their feces. F-specific phage concentrations in the feces of Canada geese and pigeons, which are normally low, increased greatly the same day coliphage MS2 was added to their diets. F-specific phage concentrations decreased to the original low levels a week after the phage-spiked feed was removed. Geese kept in pens that were cleaned regularly to reduce fecal-oral contamination had significantly lower somatic coliphage concentrations in their feces than wild geese had in their feces. Somatic coliphage concentrations in feces of feral pigeons were typically low with an occasional fecal sample having high numbers of either one of the two types of phages seen in this population of birds. Sometimes many birds had high numbers of only one type of phage in their feces. This lasted only a day and was probably due to fecal contamination of the feeding pans by the pigeons. The degree to which birds are a source of phage indicators of fecal pollution can change in a short period of time. Thus the presence of contaminated feeding sites should be considered before ruling out animals as a possible source of fecal indicators. F-specific phages may be useful tracers for modeling viral transmission and tracking feeding habits in birds. Journal of Industrial Microbiology & Biotechnology (2000) 24, 127–131. Received 06 July 1999/ Accepted in revised form 07 November 1999     

Rapid Determination of the Presence of Enteric Bacteria in Water

A rapid and sensitive method is described for the detection of bacteria in water and various other natural substrates by the isolation of specific bacteriophage. By the addition of large numbers of the organism in question to the sample, the presence of virulent bacteriophage can be demonstrated in as little as 6 to 8 h. Fecal coliform, total coliform, and total coliphage counts were determined for over 150 water samples from several geographical areas over a period of 2 years. Computer analysis of the data shows a high degree of correlation between fecal coliforms and the coliphage present in the samples. With a high correlation coefficient between fecal coliform and coliphage counts, predictions of the fecal coliforms may be made by enumeration of the phage.     

Sunlight inactivation of fecal bacteriophages and bacteria in sewage-polluted seawater.

Sunlight inactivation rates of somatic coliphages, F-specific RNA bacteriophages (F-RNA phages), and fecal coliforms were compared in seven summer and three winter survival experiments. Experiments were conducted outdoors, using 300-liter 2% (vol/vol) sewage-seawater mixtures held in open-top chambers. Dark inactivation rates (k(D)s), measured from exponential survival curves in enclosed (control) chambers, were higher in summer (temperature range: 14 to 20 degrees C) than in winter (temperature range: 8 to 10 degrees C). Winter k(D)s were highest for fecal coliforms and lowest for F-RNA phages but were the same or similar for all three indicators in summer. Sunlight inactivation rates (k(S)), as a function of cumulative global solar radiation (insolation), were all higher than the k(D)s with a consistent k(S) ranking (from greatest to least) as follows: fecal coliforms, F-RNA phages, and somatic coliphages. Phage inactivation was exponential, but bacterial curves typically exhibited a shoulder. Phages from raw sewage exhibited k(S)s similar to those from waste stabilization pond effluent, but raw sewage fecal coliforms were inactivated faster than pond effluent fecal coliforms. In an experiment which included F-DNA phages and Bacteroides fragilis phages, the k(S) ranking (from greatest to least) was as follows: fecal coliforms, F-RNA phages, B. fragilis phages, F-DNA phages, and somatic coliphages. In a 2-day experiment which included enterococci, the initial concentration ranking (from greatest to least: fecal coliforms, enterococci, F-RNA phages, and somatic coliphages) was reversed during sunlight exposure, with only the phages remaining detectable by the end of day 2. Inactivation rates under different optical filters decreased with the increase in spectral cutoff wavelength (50% light transmission) and indicated that F-RNA phages and fecal coliforms are more susceptible than somatic coliphages to longer solar wavelengths, which predominate in seawater. The consistently superior survival of somatic coliphages in our experiments suggests that they warrant further consideration as fecal, and possibly viral, indicators in marine waters.     

Bacteriophage ecology in a small community sewer system related to their indicative role in sewage pollution of drinking water

In view of various studies looking for the merit of coliphages as indicators of water pollution with viruses originating from faecal material, a small agricultural community (population of approximately 1500 inhabitants of all ages, 2-3 km from Haifa) was selected in order to understand these bacteriophage ecology (F-RNA and somatic coliphages) in its sewer and oxidation pond system. Along the sewer lines, it was possible to isolate constantly both bacteriophage types (F-RNA and somatic coliphages) at 10(2)-10(4) plaque-forming units (pfu) ml(-1). The average numbers of somatic and F-RNA phages isolated from oxidation pond were 10(3)-10(4) pfu ml(-1); however, somatic coliphages were undetectable for several months (April-August). Significant high correlation (0.944 < R(2) < 0.99) was found between increased anionic detergent concentrations and F-RNA coliphage numbers. Infants less than 1 year old excreted both phage types and few only F-RNA coliphages (at high numbers > 10(5) pfu g(-1)) for up to 1 year. The excretion of F-RNA coliphages was highly linked to Escherichia coli F(+) harborage in the intestinal track as found in their faecal content. Finally, three bacterial hosts E. coli F(+), F(-) and CN(13) tested for survivability in sewage filtrate revealed that E. coli F(+) had the highest survivability under these conditions. Presence of somatic and F male-specific phages in sewer lines of a small community are influenced by several factors such as: anionic detergents, nutrients, temperature, source (mainly infants), shedding and survival capability of the host strain. Better understanding of coliphages ecology in sewer systems can enhance our evaluation of these proposed indicator/index microorganisms used in tracking environmental pollution of water, soil and crop contamination with faecal material containing enteric viruses.