Biology Reference
In-Depth Information
Current routine monitoring tests
146
are only effective for single proto-
zoan pathogens, are time consuming, and are labor intensive, which leads
to underreporting of outbreaks in many countries. The need for improved
surveillance of drinking water for protozoan parasites has necessitated the
search for faster, more specific testing for these pathogens. More accessible
and reliable tools for protozoan detection have been proposed, including
PCR, DNA microarrays, mass spectroscopy, and biosensors.
205
Rochelle et al.
67
described a PCR-based assay for the detection of
C. parvum
and
Giardia lamblia
from water samples that was able to detect
from 1 to 10 oocysts and 5-50 cysts in pure and seeded samples, respectively.
To generate this level of sensitivity, however, they performed two succes-
sive rounds of amplification. The convenience of detecting more than one
pathogen simultaneously lead to the study of multiplex PCR systems.
207
However, the need to have the different primer sets function in the same
conditions limits the specificity of the primers.
The development of DNA microarray systems holds promise for more
rapid, sensitive, and specific detection of protozoans in water samples. They
have successfully been applied to phylogenetic studies
70
and are now being
adopted for detecting and discriminating between the various protozoan
pathogens.
74
Lee et al.
68
described a DNA microarray system that is able to
detect approximately 1 × 10
3
copies of the SSU-rRNA gene of
C. parvum
,
which corresponds to about 50 oocysts; however, this is still far above the
infectious dose of 1 oocyst.
164
Miniaturization of molecular methods holds
the promise of being able to attain the single (oo)cyst detection, especially
when combined with microfluidic systems.
151
However, the speed of the
tests cannot jeopardize the sensitivity and specificity that is needed for
these methods to be adopted as standard protocols because the approval of
regulatory bodies is required.
8.3.6. Cyanobacteria
Cyanobacteria (
Anabaena
, Aphantiomenon,
Microcystis
) and other blue-
green algae can form heavy growths on the surfaces of ponds, lakes, and
other bodies of water. These water blooms appear most often during hot
weather and where the water body is eutrophic. Toxins produced by these
organisms are potentially hepatotoxic, nephrotoxoic, and carcinogenic.
106
Guidelines have been proposed for toxin levels for consumption but not
for the potential risk for cancer, although microcystin toxins are likely to be
tumor promoters.
208
In the United States, the exposure limits have been set
to 1.0 µg L
−1
; in Canada, they are 1.5 µg L
−1
; in Australia, they are 1.3 µg L
−1
.
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