Report No FR/D0005

SURROGATE VIRAL INDICATORS

FR/D0005

Aug 1991

SUMMARY

I OBJECTIVES

  1. To evaluate a specific bacteriophage test as a measure of the efficiency of water treatment for virus removal, and suggest necessary modifications.
  2. To assess the value of coliphages as indicators of faecal contamination in waters of different quality.
  3. To assess the suitability of coliphages as indicators of quality in water samples where long delays exist between sampling and analysis.

II CONCLUSIONS

A method developed at RIVM, the Netherlands for enumeration of F-specific coliphages appeared to be effective, but did not prove to be completely reliable, owing to problems with the host organism, S. typhimurium WG49. This engineered host organism is genetically unstable, and requires careful handling. Experience suggests that some laboratory workers will have more success with the method than others.

An adsorption-elution method for concentrating bacteriophages from large volumes of water was developed, and proved reasonably effective, though unsuitable for saline waters. It was time-consuming, however, and results showed considerable variability. An alternative method of elution, which would have improved the methodology, was unfortunately unsuccessful.

In the first trial carried out at a sewage works, coliphages appeared to respond in a similar way to enteroviruses to the treatment processes studied, while the response of total and thermotolerant coliform bacteria was quite different. In the second trial, there appeared to be less removal of coliphages than bacterial indicators, but no useful virological results were obtained.

Coliphages were less numerous than bacterial indicators in river water and were sometimes found in the absence of enteroviruses. However, no samples were tested which did not contain coliphages, so it cannot be deduced whether or not they would be more sensitive indicators than bacteria.

Survey of a water treatment works suggested that enteroviruses, though present in only low numbers in the raw water, were not removed by the treatment processes to the same extent as bacteria, in percentage terms. Phages seemed to be removed to a greater extent than viruses, and were not detected in samples of slow sand filter effluent, when bacterial indicators and enteroviruses were found.

Use of coliphages as pollution indicators is included as a tentative method in APHA Standard Methods. In tests on recreational waters, somatic coliphages were found to correlate positively with thermotolerant coliform organisms and faecal streptococci, but correlation coefficients were not high (0.8 and 0.62 respectively). F-specific coliphages were below the limit of detection in all but one sample tested.

Coliphages would be no better than coliform bacteria as pollution indicators in situations where there is a long delay between sampling and analysis.

F-specific coliphages survived better than polioviruses when exposed to free chlorine sufficient to give a residual concentration of 0.3 mg/1 after 30 minutes. However, the opposite was true with a higher residual. F-specific phages were very much more resistant to combined chlorine (pre-formed monochloramine) than were polioviruses. F-specific coliphages therefore have potential use as model viruses in disinfection trials.

In storage tests, the rate of inactivation of viruses in the dark was generally much less than for phages. Somatic coliphages were much more stable than F-specific ones, and their survival was affected by increased temperature, but not salinity. F-specific phages were sensitive to both higher temperature and salinity, and their survival in sea water at 20 C was very poor, even compared with that of thermotolerant coliforms.

Coliphages were generally more resistant than polioviruses to inactivation by sunlight, with somatic coliphages being consistently more resistant than F-specific types. Polioviruses survived exposure to sunlight better in fresh water, while coliphages survived better in saline water.

Bacteriophages may therefore be useful as model viruses in certain situations, but not in all. In particular, the comparative lack of stability of F-specific coliphages with increasing temperature, means that in many situations they would not persist in the environment for as long as mammalian viruses such as polioviruses.

III RECOMMENDATIONS

Improvements are needed in the techniques for enumerating mammalian viruses in environmental samples. It is difficult to assess the value of an indicator organism when the target organism for which it is a surrogate cannot be enumerated reliably.

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