New approach for the simultaneous detection of somatic coliphages and F-specific RNA coliphages as indicators of fecal pollution

Enteric bacteriophages (somatic coliphages, F-specific coliphages or both together) are now recognized as useful viral indicators in water, shellfish, and biosolids and are being progressively included in national and international sanitary regulations. Among them, somatic coliphages have an advantage in that they usually outnumber F-RNA coliphages in water environments. Their enumeration using Modified Scholten's (MS) media, following the ISO 10705-2 standard for the growth of Escherichia coli host strain WG5, is highly efficient and a common practice worldwide. These media contain a high concentration of nutrients, which may be modified to save costs without loss of bacterial growth host efficiency. This study explored reducing the concentration of nutrients in the current formulation and/or incorporating new components to improve the host bacterial growth and/or the enumeration of somatic coliphages at an affordable analytical cost. A twofold dilution of the original MS media was found not to affect the bacterial growth rate. The addition of combinations of assayed compounds to twofold diluted MS media slightly enhanced its analytical performance without altering bacterial growth. By generating savings in both cost and time while maintaining optimal results, media dilution could be applied to design new simple applications for coliphage enumeration