Optimisation of the ISO-method on enumeration of somatic coliphages (draftISO 10705-2)

As part of the EU project "Bacteriophages in Bathing Waters" (January 1996 - June 1999) research was carried out to optimise the method for detection and enumeration of somatic coliphages in water as described in ISO/CD 10705 -2 of August 1995. It was concluded that this draft ISO standard needed to be amended in certain aspects. For determining the viable count of the host culture WG5 Escherichia coli, a membrane filtration technique should be us ed instead of spread plate technique as the latter gives lower and less rep roducible results. A freshly prepared inoculum culture of host strain WG5 s hould be used instead of a frozen inoculum culture as freezing of the inocu lum culture is found to negatively influence the phage counts. The double a gar layer method (DAL) is preferred to the single agar layer method (SAL) f or performing the phage analysis as the DAL method gives higher phage count s than the SAL method.