EVALUATION OF ENRICHMENT MEDIA FOR DETECTION OF ESCHERICHIA COLI O157:H7 IN GROUND BEEF USING IMMUNOMAGNETIC-ELECTROCHEMILUMINESCENCE

Various enrichment media were evaluated in developing a process for the rapid detection of Escherichia coli O157:H7 in ground beef samples using an immunomagnetic separation (IM)/electrochemiluminescent (ECL) procedure. Ground beef was inoculated with different levels of E. coli O157:H7 and enriched in either brilliant green bile (BGB) 2% broth, modified E. coli broth with novobiocin (mEC), mEC without novobiocin (mEC w/o N) or Gram-negative (GN) broth, Hajna containing vancomycin, cefixime and cefsuludin at 37C for 6 h. Following enrichment, boiled samples were filtered, concentrated by IM and assayed using ECL. Using this process, the presence of E. coli O157:H7 in ground beef spiked at a level of 1 cfu/10 g could be detected by IM-ECL in samples that had been enriched in BGB, mEC or mEC w/o N. IM-ECL assays that were performed on samples enriched in GN broth were inconsistent, even with inocula as high as 100 cfu of E. coli O157:H7. The boiled samples prepared after enrichment with mEC or mEC w/o N required considerable filtration time to remove particulate material; however, the boiled samples prepared after enrichment in BGB could be filtered rapidly. Thus, BGB enrichment coupled with an IM-ECL procedure allowed a more facile, and potentially more rapid, method for the detection of low numbers of E. coli O157:H7 in ground beef samples.