title: Rapid detection of Escherichia coli O157:H7 by immunomagnetic separation and real-time PCR.
abstract: 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 <5x10(2) cells ml(-1) for suspensions of E. coli O157:H7 in buffer and 1.3x10(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.
authors.affiliation: Biology Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.
authors.forename: Zhu
authors.initials: Z
authors.lastname: Fu
authors.forename: Snezna
authors.initials: S
authors.lastname: Rogelj
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Kieft
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000235:genetics*; D000818:Animals; D000911:Antibodies, Monoclonal; D002417:Cattle; D015169:Colony Count, Microbial; D003429:Cross Reactions; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics*; D005506:Food Contamination / Q000032:analysis; D018189:Immunomagnetic Separation / Q000379:methods*; D008461:Meat Products / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D018829:Adhesins, Bacterial; D000911:Antibodies, Monoclonal; D029968:Escherichia coli Proteins; C073819:eaeA protein, E coli