Bacteriophages as indicators of enteric viruses and public health risk in groundwaters

Low concentrations of all types of bacteriophages in groundwater limit their power to predict the presence of enteric viruses. There is little concordance in the literature regarding phage detection methods, thus making comparisons extremely difficult. Different authors have used different hosts, phage concentration methods, and end-point determinations. Also, markedly different volumes of sample have been employed, varying from 1 litre to 400 l. Bacteriophage concentration methods are not reproducible. There has been marked variability among groups in the natural substrates used (for example, beef extract), the type of adsorbing filter used, centrifugation instruments and conditions, and the delivery of the concentrate to the host cells. There is no consensus on the best bacterial host strain. Currently, several are employed with each showing differential sensitivities and specificities. In particular, host stability must be considered. Host stability has two components: the ability of the host to continue to be receptive to the bacteriophage after continued sub-culture, and the lack of lysogenic or temperate bacteriophage in the host cell line which may be randomly and unpredictably activated. There is a lack of consistent recovery of bacteriophages from individual faecal specimens. In particular, only approximately 3% of individual humans carry the FRNA phages. While there is some evidence to indicate that the phages multiply in sewage, it is not clear how they do so since the host pili should not be produced at lower temperatures. These ecological factors need to be understood. Of all the phages thus far studied, Bacteroides fragilis HSP40 has the highest recovery rate from individual people. However, Bacteroides, being an anaerobe, is a difficult host for routine laboratory analysis. Methods for the enumeration of F(+)-specific phages and Bacteroides phages are complex, time-consuming, costly and not reproducible. Conversely, somatic coliphage methods are simpler and results can be available in 4-6 h. The occurrence of phages and viruses in groundwater depends on physicochemical characteristics that control their fate and transport in the groundwater/aquifer environment. There are very little actual data taken from the field that allow an understanding of the ecology and life span of phages in their natural environment. Moreover, the ability of phages to serve as a source of food for other microbes needs to be understood. There has been a lack of association of bacteriophage recovery with gastroenteritis outbreaks due to enteric viruses. There is only a small epidemiological database concerning the occurrence of enteric viruses in groundwater.