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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Enzyme-Linked Immunomagnetic Chemiluminescent with Usf Das Bam Method for the Detection of Escherichia Coli O157:h7

Authors
item Gehring, Andrew
item Albin, David
item Irwin, Peter
item Reed, Sue
item Tu, Shu-I

Submitted to: Journal of Microbiological Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 19, 2006
Publication Date: December 1, 2006
Citation: Gehring, A.G., Albin, D.M., Irwin, P.L., Reed, S.A., Tu, S. 2006. Comparison of enzyme-linked immunomagnetic chemiluminescent with usf das bam method for the detection of escherichia coli o157:h7. Journal of Microbiological Methods. 67:527-533.

Interpretive Summary: Many rapid tests, that often require only a few hours for completion, have been created to detect the presence of harmful bacteria in foods. These screening tests are often used as alternatives to more conventional microbiological methods that often take days for an answer. Escherichia coli (E. coli) O157:H7 is one such harmful bacterium that has been implicated in numerous cases of foodborne poisonings. However, most rapid tests are not conclusive and therefore do not claim to confirm the presence of E. coli O157:H7 in foods. A new test called enzyme-linked immunomagnetic chemiluminescence (ELIMCL) has been developed and recently improved to now be more simplistic and semi-automated in usage. ELIMCL has been shown to conclusively detect very low amounts of E. coli O157:H7 in ground beef in the presence of other, potentially interfering bacteria. This work presents the application of ELIMCL to the detection of E. coli O157:H7 with a detection limit of approx. 1e5-1e6 live cells per milliliter of a buffered liquid. ELIMCL is also demonstrated to detect 400 bacterial cells of E. coli O157:H7 per gram of artificially contaminated ground beef in a total testing time of about 7 hours. ELIMCL is also shown to compare favorably with the USFDAs BAM method for E. coli O157:H7. Ultimately, ELIMCL may be used by food producers or food regulators to test for the presence of harmful bacteria in their products.

Technical Abstract: Rapid methods have typically been developed for the screening of this pathogen in foods in order to circumvent timely plate culture techniques. Escherichia coli O157:H7, a major foodborne pathogen, has been associated with numerous cases of foodborne illnesses. Unfortunately, many rapid methods are presumptive and do not claim to confirm the presence of E. coli O157:H7. The previously developed method, enzyme-linked immunomagnetic chemiluminescence (ELIMCL), has been improved upon to allow for fewer incidences of false positives when used to detect E. coli O157:H7, in the presence of mixed cultures, in artificially contaminated ground beef. The key feature of this assay is that it combines the highly selective synergism of both anti-O157 and anti-H7 antibodies in the sandwich immunoassay format. This work presents the application of a one-step ELIMCL to the detection of E. coli O157:H7 in pristine buffered saline with detection limits of approx. 1 e5 to 1 e6 of live cells per mL. ELIMCL was demonstrated to detect E. coli O157:H7 inoculated in ground beef at ca. 400 CFU/g after a 5.5 hr enrichment and about 1.5 hr assay time for a total detection time of about 7 hr. ELIMCL, now semi-automated, was further compared with USFDAs BAM method for E. coli O157:H7. Using McNemar's treatment, the two methods were determined to be statistically similar for the detection of E. coli O157:H7 in ground beef inoculated with mixed cultures of select bacteria.

Last Modified: 11/20/2014
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