Biology Reference
In-Depth Information
approaches are still published today in order to provide new methods or to
suggest new indicators for fecal source detection.
8
Alternative indicators include fecal anaerobes (genera
Bacteroides
and
Bifidobacterium
, spore-forming
Clostridium perfringens
), viruses (
Bacteroides
fragilis
phage, coliphages (FRNA phage)), and fecal organic compounds
(coprostanol) as described in more detail in a 2006 review
13
and sum-
marized in a table adapted from that publication (
Table 3.1
). The WHO
Guidelines present how some of these different strategies can be applied for
different types of monitoring (
Table 3.2
).
1
Alternative technologies include an adenosine triphosphate (ATP) sen-
sor system. ATP is an energy carrying molecule found in all living cells and,
as such, it can be used as an indicator for living bacteria in drinking water.
14
It is assumed that a high level of ATP correlates well with a high level of
bacteria. No limit of detection was reported. The detection can be per-
formed rapidly within a few seconds and with high sensitivity.
15
The analy-
sis is well established and is used for monitoring water quality.
16
This early
warning system was developed as part of the EU Sensowaq project, which
also designed a novel chemiluminescent method to detect enterococci.
17
3.3.1. Correlation of indicators with pathogen presence
As described above, the traditional method of water monitoring, aimed at ensur-
ing water safety, was microbiological monitoring, especially for
E. coli
(syn. fecal
coliform counts or thermotolerant coliform counts). However, in recent years
it has been recognized that there is not always a strong correlation between
fecal indicator positive results and pathogen presence. This was highlighted by
the emergence of
Cryptosporidium
as a major cause of waterborne outbreaks,
where often the fecal indicator testing had shown absence of
E. coli
.
18
This is
likely to be because
E. coli
is sensitive to chlorination, whereas
Cryptosporidium
demonstrates considerable resistance. Many viruses also demonstrate chlorine
resistance
19
and norovirus (NoV) outbreaks have been reported where
E. coli
was shown to be absent.
18
The lack of correlation between indicator
E. coli
and
Cryptosporidium
as well as
Salmonella
was again demonstrated in a Canadian
study in 2007 and 2008 (
Fig. 3.4
). Another reason for a lack of correlation
may be different degrees of persistence in water. The short persistence time of
indicator organisms has also been quoted as one further disadvantage of this
approach.
13
Most of the above examples deal with a lack of correlation between
fecal indicator bacteria (FIB) and viral and protozoan pathogens. Recently,
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