Existing Methods of Waterborne Pathogen Detection - Waterborne Pathogens: Detection Methods and Applications - page 53

This enables the detection of unculturable organisms, though one draw-
back is viability determination. It is important to note that the molecular-
based technique could be also used to detect conventional fecal indicators
including E. coli .
3.4.1. Viruses
Enteric viruses are not routinely monitored in water samples due to practical
reasons. Limitations include the need to concentrate large volumes due to
low numbers in the samples, the need for specialized equipment for cell
cultures, the need for highly trained personal and the overall cost of the
analysis. The prediction of viral contamination relies on the presence of
various indicators such as E. coli , total coliforms, Enterococcus , C. perfringens
spores and bacteriophage. However, if viral infections are suspected due to
water contamination, direct detection of the enteric viruses can be carried out.
Direct testing provides invaluable information to the public health authori-
ties and to researchers. Standard enteric viral recovery and detection meth-
ods are available. 20-22
Monitoring for viruses requires a two-step process, first, concentration of
the sample and second, detection of the virus. Since viral numbers are usually
very low, volumes in excess of 100 L for surface water and 1000 L for drink-
ing water have been used to ensure the ability to detect virus if present. 23
Concentration is usually achieved by filtration through positively charged
filters 20 or ultrafiltration although the latter method usually cannot handle
larger volumes then 20L. 24 Often a second filtration method step may be
necessary to reduce the volume of the sample down to 1-2 mL via organic
flocculation, polyethylene glycol precipitation or ultracentrifugation. 24,25
Sampling and analytical procedures for the virological analysis of water are
well documented. 26
It is difficult to culture viruses since they do not grow outside of their
host. Methods documenting virus infection, and multiplication, in estab-
lished cell lines have been developed. This approach evidently indicates
infectivity, though the methods are obviously time-consuming and require
highly trained technicians.
Historically, cell culture follows the concentration step, and is consid-
ered the gold standard for determining the infectivity of the isolated virus.
A variety of cell lines have been used such as buffalo green monkey kidney
cells and human lung carcinoma cells (A549). However, since no single line
is able to propagate all viruses, even in the same viral group, many different
cell lines have been employed. 25 Furthermore, although some enteric