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beads conjugated with antirabbit immunoglobulin antibodies. 69 A simi-
lar approach was used by Dunètre and Dardé (2005) for T. gondii using
commercially available goat antimouse IgM coated magnetic beads and an
in-house produced monoclonal antibody. 70 However, this antibody lacked
in specificity and a more specific antibody was later used by the same
authors (2007) for tap and surface water (10-20L) concentrates seeded
with approximately 100 sporulated oocysts with recoveries of 74.5% from
drinking water and 30.6% and 37.1% from two different surfaces waters.
For this antibody, acid elution was not sufficient enough, but sonication was
required to release the sporocysts. This antibody crossreacted with sporo-
cysts of Hammondia hammondi , Hammondia heydorni , and Neospora caninum .
Obtaining antibodies specific enough to isolate a microorganism from a
complex background that also may contain closely related microorganisms
is one of the major challenges in development of IMS methods.
IMS is also used for recovery of bacteria, mainly from enrichment
broths, in analysis of pathogens in food, environmental, and clinical sam-
ples. Magnetic beads with antibodies against common pathogen that can
be encountered in water, such as EPEC, E. coli O157 and Salmonella are
commercially available from several suppliers. Cationic beads for recovery
of viruses are also available, and IMS for viruses has been reported in several
research studies. 71 Automated IMS systems such as Pathatrix ® Auto System
(ABI) will probably increase the number of pathogens against which anti-
bodies are available.
Flow-through IMS techniques have been developed, with Ramadan
and colleagues reporting a continuous flow magnetic separation system for
Cryptosporidium and Giardia isolation and concentration. 72 Incubation of
the protozoan pathogens with the IMS beads occur as prescribed in USEPA
Method 1623. Subsequently, the bead-pathogen complexes enter the flow-
through system. Here, as the magnetic particulate matter passes through the
channel it is repeatedly captured and released by the rotation of an external
permanent magnet. Finally, the concentrated sample is captured by another
magnet at the end of the channel. This is illustrated in Fig. 4.8 . The aim of
the multiple stages performed away from the wall was to avoid the problems
of aggregation sometimes observed in IMS. Due to the relatively high mag-
netic particle concentrations, large aggregates are formed in which impuri-
ties might be trapped. This system was reported to concentrate samples of
50 mL down to 1 mL, with efficiencies comparable to the existing method,
performing IMS in smaller volumes in a tube, for both tap ( Fig. 4.9 ) and
secondary effluent water. When testing tap water samples, Ramandan et al.
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