Isolation of Escherichia coli 0157:H7 Using 0157 Specific Antibody Coated Magnetic Beads

Abstract

Escherichia coli 0157 specific antibody, coated on magnetic beads, was used to concentrate and remove the E. coli 0157:H7 from mixed cultures and meat samples. The problem of nontarget organism carryover was addressed by adding Protamine to the culture-bead sample, washing the beads three times in saline, and changing the test tubes with each wash. These modifications reduced the nontarget colony counts obtained from uninoculated meat samples. This procedure enabled consistent recovery of E. coli 0157:H7 from inoculated meat samples. The percentage of E. coli 0157:H7 cells captured, compared to the total number of cells captured, ranged from 48 to 100%. Two strains of E. coli 0157, H7 and :non-H7, appeared to compete with one another and thus reduce or prevent isolation.

Immunomagnetic separation as a sensitive method for isolatingEscherichia coliO157 from food samples

“…IMS has been shown to be more sensitive than direct culture for isolation of E. coli 0157 from artificially mixed cultures and inoculated meat samples [17,18], but before combining the technique with our enrichment culture we addressed problems encountered in these studies. Fratamico and colleagues [17] reported 36-60 % recovery of E. coli 0157 by IMS from suspensions in PBS; the recovery rate of 97 % described in this report is higher, but may have been influenced by the fact that the separations were carried out in enrichment medium, which may have allowed continued growth of the organisms during the 30 min separation period.…”

“…Fratamico and colleagues [17] reported 36-60 % recovery of E. coli 0157 by IMS from suspensions in PBS; the recovery rate of 97 % described in this report is higher, but may have been influenced by the fact that the separations were carried out in enrichment medium, which may have allowed continued growth of the organisms during the 30 min separation period. Both previous studies [17,18] found non-specific binding of organisms other than E. coli 0157 to both beads and tubes to be a problem and used washing procedures in PBS with foetal bovine serum 1 % v/v [17] or physiological saline [18] and silicon treated tubes in attempts to overcome this. Adherence of E. coli 0157 or background organisms to either untreated or siliconized tubes was not found in the present study; although speculative, this may have been due to the use of polypropylene tubes rather than the glass tubes used previously [18].…”

“…Both previous studies [17,18] found non-specific binding of organisms other than E. coli 0157 to both beads and tubes to be a problem and used washing procedures in PBS with foetal bovine serum 1 % v/v [17] or physiological saline [18] and silicon treated tubes in attempts to overcome this. Adherence of E. coli 0157 or background organisms to either untreated or siliconized tubes was not found in the present study; although speculative, this may have been due to the use of polypropylene tubes rather than the glass tubes used previously [18].…”

Magnetic separation techniques in diagnostic microbiology

“…These antibodies can be linked to the beads either directly or indirectly, using beads precoated with anti-mouse or antirabbit antibodies ( Fig. 1) (38,46). The IMS technique has several advantages.…”

Determination of the Sensitivity of a Rapid Escherichia coli O157:H7 Assay for Testing 375-Gram Composite Samples

“…A technique for cell separation using immunomagnetic beads has been developed for the detection of E. coli O157:H7 (7,11,18,21). This relatively simple and rapid method uses iron-impregnated latex beads coated with an antibody against E. coli O157 which are added to samples that have already been enriched.…”