Submitted to: American Society of Microbiologists Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 7, 2005
Publication Date: June 1, 2005
Citation: Durso, L.M., Keen, J.E. 2005. Comparison of immunomagnetic separation techniques for the detection of shiga-toxigenic Escherichia coli O157:H7 from feces of naturally-infected cattle. [abstract] American Society of Microbiologists. p. 259.
Immunomagnetic separation (IMS) is widely used for the selective enrichment of Shiga-toxigenic Escherichia coli O157 (STEC O157) from a variety of complex sample matrices, especially samples with high background flora. In conventional E. coli O157 IMS methods 1 ml of an enriched sample is incubated with anti-O157 paramagnetic beads, which are removed using a magnetic particle concentrator (MPC), and plated on selective agar. A second system, called Pathatrix, re-circulates an entire 250 ml sample over the paramagnetic beads.
Based on the larger volume sampled, we hypothesized that the Matrix Pathatrix system would be more sensitive than Dynal Dynabeads for STEC O157 detection from feces of naturally infected cattle, and that enrichment methods and plating media would also affect recovery rates.
Fecal samples (n=102) were collected from two beef feedlots in Nebraska. IMS was performed on 0 h and 6 h enrichment broths using either the Dynal Dynabeads and MPC, or the Matrix Pathatrix. Samples were plated onto Chrom Agar (CA) and CA containing tellurite (TCA). Suspect colonies were confirmed using serology and PCR. Results were analyzed using logistic regression for clustered data using SAS Proc Genmod, where a cluster was the fecal sample cultured using a matrix of the above conditions, for a total of 8 conditions per sample.
There were significant overall effects of IMS method, time, and plate. Pathatrix outperformed Dynal (odds ratio [OR] = 1.55, 1.19-2.20 95% CI), 6 h enrichment was better than 0 h (OR=2.18, 1.40-3.41 95% CI), and TCA was better than CA (OR=1.82, 1.33-2.49 95% CI). The most sensitive combination was Patahtrix IMS after 6 h enrichment plated onto TCA, which found 49 of the 102 fecal samples positive, followed by the Dynal IMS after 6 h enrichment plated onto TCA, which found 37 of 102 fecal samples positive. There were no significant differences between the two IMS methods at O h enrichment. No single method could account for all positive samples.
In conclusion, the IMS method can affect recovery rates, as can enrichment time and plating media. Pathatrix IMS was more sensitive than Dynal IMS methods after 6 h enrichment plated onto TCA.