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.
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