Scientific Publications by FDA Staff

Lett Appl Microbiol 2017 Sep;65(3):213-9

Comparison of immunomagnetic separation beads for detection of six non-O157 Shiga toxin-producing Escherichia coli serogroups in different matrices.

Kraft AL, Lacher DW, Shelver WL, Sherwood JS, Bergholz TM

Immunomagnetic separation used with culture based methods has been a useful technique in the detection of pathogens. However, previous studies have not answered many of the necessary questions for real world applications. The objective of this study was to assess the efficacy of different IMS bead types in recovery of the correct serogroup from a mixture of big six non-O157 STEC strains. To determine the impact of different matrices on recovery, samples of sterile phosphate buffered saline (PBS), sterile and non-sterile cattle feces, ground beef, and lettuce were inoculated with 10 CFU ml-1 mixture of isolates representing the six serogroups. After a 6 h incubation at 37 degrees C, samples were mixed with IMS beads from three different commercial sources and plated on eosin methylene blue agar (EMB). Three suspect E. coli colonies were selected from each EMB plate and multiplex PCR was used to determine the serogroup. The rate of correct identification varied with the serogroup, IMS bead manufacturer, and matrix. Overall, recovery of the correct serogroup became less likely with increase in matrix complexity, with enrichments containing lettuce having the greatest number of bead types with significantly lower likelihood of correct recovery compared to recovery in PBS.