PhiX-174 phage concentration in rainwater by skimmed-milk flocculation

Rainwater, as a sustainable source of drinking water, is becoming increasingly important worldwide. Appropriate microbiological techniques are needed to ensure the acceptability of rainwater for potable uses. Bacteriophage has been widely used as a viral indicator in water studies, and its concentration is an important step when sampling several litres of water. Skimmed-milk flocculation (SMF) is a simple method for viral recovery, and its efficiency has already been assessed for some viruses. However, there are only a few records on bacteriophage recovery using SMF, and none with PhiX-174 coliphage, an important surrogate for human enteroviruses. Thus, this work aimed to evaluate the effectiveness of the SMF technique on the concentration of PhiX-174 coliphage in rainwater. 3 L of rainwater samples were artificially spiked with PhiX-174 and were concentrated to 10 mL volumes by SMF. The phage enumeration on the concentrated samples were evaluated by a standard double layer plaque assay. From the 6 samples tested, the average recovery was 22.8 ± 15.2%, ranging from 10.8 to 52.8%. This is the first time that SMF is applied for PhiX-174 coliphage recovery, and in rainwater. Therefore, SMF is a cost-effective method that can effectively be used to recover bacteriophage PhiX-174 in water samples.