Antibody-direct epifluorescent filter technique for rapid, direct enumeration of Escherichia coli O157:H7 in beef.

Artificially inoculated Escherichia coli O157:H7 was directly enumerated in ground beef and beef exudate, without enrichment or selection, by the antibody-direct epifluorescent filter technique (Ab-DEFT). The total assay time of the Ab-DEFT was less than 1 h. The beef was homogenized, treated for 15 min with trypsin and Triton X-100, and passed through a 5-microns-pore-size prefilter and then through a 0.2-microns-pore-size black polycarbonate filter. The final filter was stained directly with fluorescein-labeled anti-O157 polyclonal antibody, rinsed, and examined by epifluorescence microscopy. The sensitivity of the Ab-DEFT was compared with that of a standard enrichment culture technique. Both methods reliably determined the presence of the pathogen in beef at 16 CFU/g. The Ab-DEFT was also useful for quantifying the pathogen and monitoring its growth in beef.