Biology Reference
In-Depth Information
Thereafter, the eluted material is concentrated by centrifugation or using a
Filta-Max
®
concentrator apparatus.
Filtration can either be achieved using a pumping system, in the labora-
tory or in the field, or using a pressurized source such as a tap. Although
designed for
Cryptosporidium
oocysts and
Giardia
cysts, the filters have been
used for concentration of other parasites from drinking and environmental
water, for example
Toxoplasma
52-54
and microsporidia.
55
Ultrafilters have been used as a more cost-effective alternative to
capsule filters. In 2001, Simmons III et al. compared the concentration
and detection of
Cryptosporidium
oocysts in seeded 10 L samples (100-
150 oocysts) of reagent water and surface water using Envirocheck™
capsules and Hemoflow F80A ultrafilters (MWCO 80 kDa, Fresenius).
56
They concluded that for reagent water, the capsule filter gave a some-
what higher recovery (46%) than the ultrafilter (42%), but the differ-
ence was not significant. For seeded surface water samples, the recovery
remained at 42% for ultrafilters but was only 15% for the capsule filter.
Hill et al. compared Envirochek™ HV capsules with F200NR ultrafil-
ters (Fresenius) using tap water (100 L) and two different seeding lev-
els, 150 (low) and 10
5
(high), of
Cryptosporidium
oocysts and
Giardia
cysts.
57
For both seeding levels, recovery was higher with the ultrafilter
for
Cryptosporidium
with the biggest difference observed for the low
seeding level (51 ± 18% versus 3.9 ± 1.7%). For
Giardia
, recoveries were
quite similar at both seeding levels. It should be noted that for the high
seeding level, no secondary concentration (centrifugation and IMS) was
required and thus, only the effect of the filtration step was seen. A com-
parison of recovery of
Toxoplasma gondii
was performed using a reusable
hollow-fiber filter (Microza membrane, Pall) and Envirochek
®
HV cap-
sules and different types of water (10 L fresh water and seawater) with
different seeding levels (100, 1000, and 10,000 oocysts) with similar
results for both filter types.
53
Another alternative for smaller volumes is flat membrane filtration.
The ISO-standard 15553:2006 contains a protocol for concentration of
Cryptosporidium
oocysts and
Giardia
cysts using 142mm cellulose acetate
membrane (pore size ≤2µm) where, after filtration, particulate matter is
released from the membrane by gentle rubbing of the filter in the pres-
ence of 0.1% Tween80. For more information on membrane filtration, see
Section
4.4.3
.
Depending on the downstream application, factors other than recov-
ery rate may be worth considering when choosing filters. The smaller
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