Comparison of immunomagnetic separation and cultural methods in detection of
Escherichia coli O157 over two-year period
S. Vidovic1, J. J. Germida2, and D. R. Korber1
Applied Microbiology and Food Science1, Soil Science2, University of Saskatchewan, Canada
3. Cultural method
4. Sensitivity of enrichment broths
Detection of E.coli O157 by latex agglutination
Escherichia coli O157:H7 has emerged as a
TSB broth with
pathogen of increasing public health concern. The low
infectious dose and a wide range of clinical manifestations,
including life – threatening hemolytic uremic syndrome (HUS)
make human infections particularly severe and potentially
lethal. Ruminants, especially cattle have been implicated as
the primary reservoir of E. coli O157:H7 from where it can
enter the environment and further food chain. Jones, D. L.,
(1999); Meng, J., and Doyle, M. P. (1998) underlined that E.
coli O157:H7 outbreaks have attributed to a diverse range of
sources, including swimming pools, water supplies, raw
In preliminary study three different enrichment media were tested; the most favorable enrichment media for E. coli O157 was
vegetables and more commonly beef products. In view of the
mEC broth supplemented with novobiocin (20 mg/L).
potential severity of infections caused by E. coli O157:H7, it is
Arrow points at E. coli O157 colony isolated on ctSMAC plate among a group of
essential that sensitive methods be used in studies designed
to elucidate further the reservoirs of the organism and routes
5. Sensitivity of IMS and Cultural methods – Point study
6. Sensitivity of IMS and Cultural methods – Longitudinal study
In this poster we provide insight of sensitivity of
two methods, culture and immunomagnetic separation
methods, conducted during a large-scale study over two-year period. The different methods were compared in a longitudinal and
a point prevalence studies that comprised over 1600 samples of water, soil, manure slurry and cattle feces.
1. Methods layout
Assays for isolation of E.coli O157
2. Immunomagnetic beads in action
IMS M ethod
Only by IMS
Only by Cultural Conformation by
IM S M ethod
Cultural M ethod
Only by IM S
Only by Cultural Conformation by
Both M ethods
Over summer 2004, 860 fecal bovine samples were tested by both methods. Capability of two methods
Sensitivity of IMS and cultural methods in detection of E. coli O157 at four feedlots/farms over 8 month
to isolate E. coli O157 bacterium among many other organisms is shown in this graph.
z During the longitudinal study 57 isolates of E. coli O157 were detected in cattle feces while in the point prevalence study 141 organisms of E. coli O157
were isolated also from cattle feces. Immunomagnetic separation method (IMS) used in both studies showed to have higher sensitivity than the cultural
method. In the longitudinal study 80.6 and 38.7% of positive samples were detected by IMS and cultural methods, respectively. IMS method was capable to
identify 61.3% of positive samples which cultural method could not detect but in other hand cultural method identified 19.3% of positive sample which IMS
failed to identify. In the point prevalence study which exposed these methods to much higher diversity (20 feedlots) and bigger sampling base, IMS method
detected 74.8% of positive samples while cultural method was able to detect 64%. This time IMS failed to detect 25.2% of positive samples while cultural
z In both studies we got surprising results, from one fifth to one fourth of positive samples were undetectable by IMS method. Based on some other studies
(Laegreid, at al., 1999: Jakson, et al., 1998) IMS and enrichment broth selection played a key role in the isolation of this organism, however it is clear from this study that more effective IMS method (enrichment and IMS itself) is needed. Development of such method remains an area of active research in this lab.
z IMS method was not able to detect 20% and 25% of E. coli O157 population in both studies, respectively.
Arrow points at captured organism by three immunomagnetic beads.
z Further improvement of sensitivity for IMS method (enrichment step).
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