Existing Methods of Waterborne Pathogen Detection - Waterborne Pathogens: Detection Methods and Applications - page 52

3.4. DIRECT DETECTION OF PATHOGENS
In contrast to the fecal indicator approach, direct detection looks for
the presence of specific pathogens. For example, in the UK it was a regula-
tory requirement until 2008 for water companies to perform daily moni-
toring of the finished water to check for the presence of Cryptosporidium .
Methods for direct detection have become more popular with the growing
awareness that fecal indicator organism monitoring alone cannot guarantee
water safety.
However, due to low numbers of pathogens, direct microbiological test-
ing presents a unique challenge. The requirement to detect a single organ-
ism in a 100 mL water sample has been compared to the problem of finding
a single coffee bean in 40,000 Olympic-sized swimming pools.
This section will cover some of existing microbiological approaches to
direct detection in addition to mentioning other established approaches,
such as molecular methods, for the detection of different categories of
pathogens. However, advances in molecular methods will be covered in
Chapter 8, and the main focus of this topic in Chapters 5-10 is upon these
advances and other new technologies/techniques which provide an oppor-
tunity for improved direct detection.
As described above, the traditional method of detection and enumeration
of pathogens has relied on selective culture and standard biochemical meth-
ods. This has been applied for both the monitoring of indicator organisms as
well as the direct detection of specific pathogens. One potentially important
advantage is that, since the monitoring method relies on multiplication and
growth of the pathogen, the methods detect viable pathogens. This is very
useful if performing validation monitoring of finished water since it is only
viable pathogens which pose a public health risk. However, the presence
of nonviable pathogens in finished water may also be useful information
since it could indicate problems with either the source water or some part
of the treatment process. Further disadvantages are that culturing of many
organisms is challenging or, at the present time, not yet possible. And each
pathogen requires specific conditions, thus rendering a full scale screening of
all potential pathogens and a large and expensive assay to perform.
An alternative approach is the application of molecular methods. The
principal tool of most molecular-based studies is the use of polymerase
chain reaction (PCR) to evaluate the presence of selected pathogens by
detection of its specific pathogenic genes or small-subunit ribosomal RNA.