A direct membrane filter method for enumerating somatic coliphages in drinking water

The application of a simple membrane filter method to enumerate specific somatic bacteriophages of Escherichia coli, using E. coli C as host strain, from drinking water samples was studied. The efficiency of the method using cellulosic membrane filters, samples pretreated with magnesium ions and Tween 80 added to agar medium-host cell lawns ranged from 68.9 to over 112%, depending on the phage content of the sample. To avoid the pre-treatment of the sample with magnesium salts, electropositive-charged filters of cellulosic ester (HA-PEI and HA-Nalco) and Virosorb-1MDS filters were tested in conjunction with the simple membrane filter method. The electropositive filters showed wide bacteriophage recovery rate intervals depending on the sample treatment, ranging between 31.4 and 96.2% for ester-type filters, and a mean recovery lower than 2.2% for Virosorb filters. On the other hand, it was proved that the use of Tween 80 as an eluent improved somatic coliphage recovery rates for all the filters tested. In short, this methodology provides a rapid analysis (6-8 h) of the somatic coliphages from drinking water using the membrane filtration technique.