Journal
INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY
Volume 99, Issue 1, Pages 47-57Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.ijfoodmicro.2004.07.013
Keywords
Escherichia coli O157 : H7; immunomagnetic separation; real-time PCR; eaeA gene
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A method combining immunomagnetic separation (IMS) and real-time (5'-nuclease) PCR was developed to detect Escherichia coli O157:H7. Monoclonal antibody specific for the E. coli O157 antigen was added to protein A-coated magnetic particles to create antibody-coated beads. The beads specifically captured E. coli O157:H7 from bacterial suspensions. The cells were eluted from the beads and lysed by heating; the eluate was then assayed by real-time PCR, using primers and probe specifically targeting the eaeA gene of E. coli O157:H7. Approximately 50% of the cells in suspension were captured by the beads and detected by real-time PCR. No cross-reactivity was detected when other strains of E. coli were tested. This method was applied to detect E. coli O157:H7 from ground beef. Both cell capture efficiency and real-time PCR efficiency were reduced by meat-associated inhibitors. However, we were still able to detect up to 8% of E. coli O157:H7 from inoculated ground beef samples. The detection sensitivity varied among ground beef samples. The minimum detection limit was <5 x 10(2) cells ml(-1) for suspensions of E coli O157:H7 in buffer and 1.3 x 10(4) cells g(-1) for E. coli O157:H7 in ground beef The combination of IMS and real-time PCR results in rapid, specific and quantitative detection of E. coli O157:H7 without the need for an enrichment culture step. (C) 2004 Elsevier B.V. All rights reserved.
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