An evaluation of two bacteriophages as sewage tracers

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Two bacteriophages — phage 80 of Staphylococcus aureus and a P2-like phage (ϕMWD 1) of Escherichia coli (H2S + ) — were evaluated as sewage tracers. Background plaque concentrations on the S. aureus host were < 1100 mL−1 in seven (raw and treated) effluents tested but, on E. coli (H2S +), they ranged from < 1100 mL−1 in oxidation pond effluents to 1.1 × 103 100 mL−1 in primary treated meatworks effluent. Thus, phage 80 appears to be a suitable tracer for both raw and treated sewage but ϕMWD 1 may only be suitable for use in secondary treated effluent. In frozen samples, concentrations of both tracer phages were reduced by 90% within 2 days, but decreased more slowly over the following 68 days to around 5% of the original (unfrozen) titre. In a field test, the two phages were used simultaneously to trace the movement of oxidation pond effluents down a river system. Timing of assay of frozen samples and the advantages and limitations of bacteriophages as sewage tracers are discussed.