Biology Reference
In-Depth Information
has also been utilized for virus detection.
20
For protozoa an LOD of 100
parasites per liter was reported, so preconcentration steps are needed.
24
Flow cytometry has been utilized for the detection of
Cryptosporidium
(Vesey) and rotavirus
22
in drinking water; the detection of bacteria
23
and
the protozoa
Cryptosporidium
and
Giardia
25
in wastewater; the detection of
marine viruses
26
and bacteria in surface water; the detection of
Legionella
,
27
Cryptosporidium
28
and bacteria
29
in groundwater; and the detection of
Giar-
dia
21
in feces.
Table 5.2
summarizes the above results, giving information
about the detection approach, LOD and sample-processing requirements.
Flow cytometry has also been used to distinguish between viable and viable
but nonculturable bacteria.
30
One drawback of flow cytometers is that they are large and expensive
machines. There has been much progress in the development of miniatur-
ized systems, although the typical “portable” system reported is still some-
what large. A 2012 paper by Keserue and co-workers described the use of a
portable flow cytometer for disaster relief.
31
However, this system was still
relatively large, measuring 43 × 37 × 16 cm and weighing 17 kg. Some prog-
ress has been made toward very small, microfluidic scale flow cytometry,
20,32
and this is discussed in more detail in Chapter 10.
An alternative to flow cytometry is solid phase cytometry (SPC). In
SPC, the principles of epifluorescence microscopy and cytometry are
combined. Microorganisms on a filter surface are fluorescently labeled and
automatically counted by a laser scanning device. Subsequently, the data
for each fluorescent spot are analyzed using epifluorescence microscopy.
The major advantages of this system are the short analysis time per fil-
ter and the low detection limit of only a few fluorescent particles. Viable
bacteria in drinking and ultrapure water have been detected via SPC.
33
Fluorescence in situ hybridization (FISH) protocols for the quantification
of
Vibrio cholerae
34
and
Legionella
with SPC have also been developed as a
platform to improve immunofluorescence-based detection and enumera-
tion of
Cryptosporidium
.
35
5.2. SPECTROSCOPY
Spectroscopy is the interaction of radiated energy with matter, result-
ing in absorption, reflection or scattering (both elastic and inelastic). It pro-
vides information about the characteristics of the material. There are many
different types of spectroscopy, including infrared (IR), Raman and multi-
wavelength UV-vis spectroscopy.
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