Development and evaluation of a colorimetric coliphage assay detection system
A Colorimetric Coliphage Assay Detection System (CCADS) that is composed of a Liquid Colorimetric Presence-Absence (LCPA) method and a Colorimetric Agar-Based (CAB) method was developed to overcome the limitations imposed by the Standard Methods for the Examination of Water and Wastewater agar-based coliphage method (APHA method). Both CCADS methods are based on the induction of β-galactosidase in Escherichia coli and the release of the enzyme through a lytic cell infection. The released enzyme then cleaves a chromogenic substrate which produces a colored reaction product.
The CCADS was evaluated against the APHA method under laboratory conditions using a common sewage coliphage strain as a model (American Type Culture Collection- 13706-B2), and under field conditions using water samples collected from four different sources. During the laboratory evaluation, both the LCPA and CAB methods were found to be superior in coliphage detection to the APHA method because: 1) the LCPA and CAB methods were easier to read and interpret than the APHA method, 2) the LCPA and CAB methods were not subject to false positive results, 3) the LCPA method theoretically detected fewer coliphage particles than the APHA method, and 4) the CAB method detected roughly twice the number of coliphage particles than the APHA method. During the field evaluation, the results indicated: 1) the LCP A method was as reliable as either the CAB or APHA methods in coliphage detection, 2) the LCP A and CAB methods were easier to read and interpret than the APHA method, 3) neither the LCPA method nor the CAB method were subject to false positive results, 4) the CAB method detected more coliphages than the APHA method under conditions of high fecal pollution, but both methods performed equally well in coliphage detection under conditions of low fecal contamination, and 5) the LCPA and CAB methods were equally as sensitive in coliphage detection as the APHA method.
Finally, the coliphage group proved to be a useful indicator of fecal pollution in nonpotable water supplies that exhibited a high degree of fecal pollution, whereas they were not shown to be useful indicators in potable water supplies that exhibited low levels of fecal contamination. The lack of coliphage detection sensitivity under conditions of low fecal contamination does not appear to be method limited, but rather the result of inefficiencies in processing environmental samples using the concentration methods currently available.