Sample Processing - Waterborne Pathogens: Detection Methods and Applications - page 102

for concentration and enrichment before useful detection could take place.
Such in situ or on-line monitoring places a great demand on sample pro-
cessing and requires its automation. Chapter 10 presents some microfluidic
approaches to automation of sample processing, although systems will be
needed to cope with larger volumes of water for which clogging is less of
a challenge.
Viral recovery and concentration techniques include ultrafiltration,
adsorption-elution using filters or membranes, 93 NanoCeram filters, glass
wool 4 or glass powder, two-phase separation with polymers, flocculation,
the use of monolithic chromatographic columns 83 ultrafilter centrifugation,
IMS, and PEG precipitation. The use of the glass wool adsorption-elution
procedure for the recovery of enteric viruses from large volumes of water
has proven to be a cost-effective method and has successfully been applied
for the routine recovery of human enteric viruses from large volumes of
water. 4 The same applies to NanoCeram filters. While many different solu-
tions are available for concentrating viruses from water, the recovery rate
generally does not exceed 60% 70 , except in particular cases 57 .
Bacteria are commonly processed using ultrafiltration, centrifugation,
and membrane filtration. The use of membrane filtration is popular as the
membranes can be immediately employed in traditional culture-based
detection techniques. Flocculation, IMS, and density gradient centrifuga-
tion are also techniques applied to bacteria, and there have been initial
studies looking at the use of NanoCeram 25 and glass wool. 1 With a move
toward more direct detection of bacteria, including addressing the concern
that some bacteria exist in viable but nonculturable states, sample process-
ing techniques will need to develop further to accommodate e.g. issues of
removal of interferents for molecular methods. In general recovery rates for
bacteria appear to be higher than for viruses ( Table 4.1 ), although there is
a high degree of variability observed depending upon factors such as water
quality, operator skill, secondary concentration efficiency, etc.
Parasites can be concentrated using ultrafiltration, flocculation, centrifu-
gation, and membrane filtration, as well as isolated using IMS. Recovery rates
are often comparable to those achieved for bacteria. Commerical tools—
available for the specific isolation of parasites, other than Cryptosporidium
and Giardia —are lacking, such that for other parasites the detection options
are either microscopic examination or molecular detection, in highly com-
plex samples. To differentiate between parasites of different species under
the microscope requires experience, which is missing at most water labo-
ratories. Molecular identification is hampered by the low concentrations of