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Contenido archivado el 2022-12-23

Distribution comparison between coliphages and anaerobic bacteria phages in water sources and their reliability as water pollution indicators

Objetivo

- To evaluate the usefulness of bacteriophages as indicators of human viruses in drinking waters;
- To determine which of the three groups of phage, somatic coliphages, F-specific bacteriophages or bacteriophages infecting Bacteroides fragilis, at present being considered as potential indicators of enteric viruses, best fulfils the indicator function;
- To determine the validity of the results in different geographical areas.
- Methods for the detection of small amounts of phages in drinking water had been either developed or improved. Presence/absence methods for the detection of bacteriophages in 100 mL of drinking water had been improved for the three groups of bacteriophages. A simple method, based in the retention of phages by a membrane of inorganic material with a honeycomb pore structure, which a recovery of about 50 % was developed for concentration of bacteriophages from 1 litre of water.
- The levels of somatic coliphages, F-specific coliphages and bacteriophages infecting Bacteroides fragilis were determined in domestic sewage of Israel and Spain. Results allowed to verify that the three groups of phages were present in similar quantities and proportions in sewage samples from the two countries. In domestic sewage somatic coliphages, which were the most abundant, and F-specific bacteriophages outnumbered significantly Bacteroides fragilis phages. Levels of the different groups of phages per 100 mL of raw sewage are the following : somatic coliphages between 105 and 5x106, F-specific coliphages between 5x104 and 106, and bacteriophages infecting B. fragilis between 103 and 5x104.

- The comparison of the microbial levels in raw sewage, non disinfected groundwater and disinfected drinking water, indicates that phages are more resistant to natural inactivation and to water treatments than faecal coliforms. Thus, in this respect bacteriophages behave more similarly to viruses than bacteria do.
- The relative frequencies of isolation of faecal coliforms and phages in disinfected waters show some differences in data from Spain and Israel. In Spain, bacteriophages infecting Bacteroides fragilis were always the most frequently isolated. Considering the period 1993-1994, the frequencies of isolation were : somatic coliphages 2.4%, F-specific phages 4.9% and phages infecting B. fragilis 13.7%. In Israel, considering the period 1992-1994, the frequencies were : somatic coliphages 5.6%, F-specific coliphages 6.6% and phages infecting B. fragilis 5.1. However, considering only values from 1994, when stronger disinfection was implemented in Israel, the distribution of frequencies was : somatic coliphages 2.1%, F-specific bacteriophages 3.1% and B. fragilis phages 12.9%, which are not significantly different from the frequencies found in disinfected water in Spain. These values and the levels of the three groups of bacteriophages in raw sewage strongly suggest that bacteriophages infecting B. fragilis rank first in resistance to natural inactivation and to disinfection, followed by F-specific bacteriophages.
- The studies on the correlation between the presence of bacteriophages and the presence of enteroviruses are not conclusive, mainly because of the extremely low frequency of isolation of viruses. No enteroviruses were isolated in the samples tested in Spain. On the contrary they were isolated in three of the samples analysed in Israel. Two of the three samples were also positive for F-specific bacteriophages and none for either somatic coliphages or phages infecting Bacteroides fragilis. However the used concentration technique requires to bring the pH of the sample to low pHs, to which most B. fragilis bacteriophages and many somatic coliphages are very sensitive.
- The study performed in Spain reveals that at least bacteriophages infecting B. fragilis are as resistant as enteroviruses to complete water treatments, as can be inferred from the values found in the source water and in the treated water.
- For the moment it has not been possible to show any clear periodic distribution of the three groups of bacteriophages studied. However some data suggest that the frequencies of isolation increase during the rainy periods. The same fact has been described for enteroviruses.
- In conclusion, the results obtained indicate that bacteriophages are found in water samples that do not contain bacterial indicators as for example faecal coliforms, despite the fact that faecal pollution, in their origin, contains more faecal coliforms than bacteriophages. Therefore, phages cross more successfully than bacteria do the multiple barriers that faecal micro-organisms found in their way from sewage to drinking water. In this respect they behave like viruses. This successful crossing of the barriers has been observed in the two areas studied, and is more evident for phages of B. fragilis , and to a minor extent for F-specific bacteriophages. Results obtained in this project are promising regarding the potential utility of bacteriophages as indicators of human viruses in drinking water.


Follow up

- Although the results obtained in this project are very promising, extensive research needs to be done before decisions may be taken regarding the potential use of bacteriophages as indicators of human viruses in drinking water. Some aspects that need to be further investigated are described below. A few of them are already being investigated by either the research groups participating in the project or other groups;
- Further determine the resistance of the different groups of phages to inactivation in their way from faeces to drinking water and when possible compare that resistance to the resistance of those groups of human enteric viruses known to be more resistant to inactivation as for example the hepatitis A viruses. This will include :
- die off rates affecting different bacteriophages in nature;
- removal of bacteriophages in all types of water treatments;
- sensitivity/resistance of bacteriophages to different disinfectants.
- Study the correlation between the presence of viruses and the presence of bacteriophages in drinking water samples. This study is difficult because of the very low frequencies of detection of human enteric viruses in drinking water samples;
- Perform epidemiological studies in order to determine whether correlation exists between the presence of bacteriophages in drinking water with the incidence of gastrointestinal diseases caused by viruses transmitted trough water.
- To improve the methods for the detection of small amounts of bacteriophages in waters, either by presence/absence tests or concentration of bacteriophages from water samples;
- To determine the levels of somatic coliphages, F-specific bacteriophages or bacteriophages infecting Bacteroides fragilis in sewage-polluted water samples in Spain and Israel;
- To determine the presence of the three groups of bacteriophages in a great number of drinking water samples in Spain and Israel;
- Collection of comparative data on the presence of bacteriophages and faecal coliforms, used at present as bacterial indicators in drinking water samples;
- Collection of comparative data on the presence of bacteriophages and enteroviruses in a fraction of the water samples tested.

Tema(s)

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Convocatoria de propuestas

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Régimen de financiación

CSC - Cost-sharing contracts

Coordinador

UNIVERSITAT DE BARCELONA
Aportación de la UE
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Dirección
645,Av. Diagonal 645
08028 BARCELONA
España

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Coste total
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