Biology Reference
In-Depth Information
however, it has been recognized that this approach is not necessarily suitable
for the assessment of emerging bacterial pathogens. Furthermore, the absence
of coliform does not necessarily indicate the absence of these pathogens. Sev-
eral reports have indicated the presence of
Salmonella
and
Shigella
in waters
where
E. coli
was not recovered.
11
Well maintained water purification and
distribution systems are able to reduce the levels of
Salmonella
and
Shigella
to
levels not associated with human illnesses. Likewise,
Yersina enterocolitica
and
Campylobacter jejuni
have also been found to be poorly correlated to coliform
levels and HPC numbers but are reduced to innocuous levels during water
treatment.
Legionella
spp. are respiratory pathogens that are naturally found in
water environments including cooling towers, hot tubs and shower heads.
Although the presence of
E. coli
can be used to indicate the potential
presence of
Legionella
spp., their ubiquitous nature makes them hard to
correlate to indicator levels at low quantities. Furthermore, although fil-
tration and disinfection methods are successful at reducing their numbers
in water treatment,
Legionella
'
s
ability to become biofilms in water sys-
tems make them hard to detect and control.
Mycobacterium avium
presents
a similar story as they are organisms with an ability to survive and grow
under varied conditions and can persist in biofilms. They are typically
more resistant to disinfection normally used in water treatment and for
that reason their numbers are not adequately represented by indicator
numbers.
Aeromonas
species have been found in a wide variety of water envi-
ronments including, rivers, lakes, storages reservoirs, sewage effluents and
drinking water sources. Their numbers have been found not to show a
relationship to coliform numbers which can lead to false negative results.
Helicobacter pylori
can be isolated from environmental sources including
water. It has been associated with gastritis, duodenal ulcers and around
50% of gastric cancer. Currently there are no regulations for the presence
of the bacteria in drinking water. Since the coccoid form of this bacteria
is nonculturable, drinking water is not directly tested for the organisms
instead
E. coli
is used as in indicator of their presence.
11
Overall, FIB are still used as the standard for fecal source tracking and
managing water quality. More and more studies each year, however, show
that fecal bacteria presence and numbers often do not correlate well with
pathogen numbers, which may be low and patchy in distribution but highly
infectious at low doses (
Fig. 3.4
).
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