Comparison of PickPen® and OctoMACS™ Immunomagnetic Separation Procedures for Confirmation of E. coli O157:H7 and Non-O157 STEC Positive Samples

Introduction: As part of the USDA MLG isolation and confirmation procedures for E. coli O157:H7 and non-O157, presumptive positive samples are plated following immunomagnetic separation (IMS) using the OctoMACS™ paramagnetic columns and sample acid treatment. The Assurance GDS^® PickPen^® device provides a rapid and simpler alternative to isolate the immunobead-captured organisms

Purpose: To compare the equivalence of immunomagnetic separation using the Assurance GDS PickPen^®and the OctoMACS™ columns for the isolation of E. coli O157:H7 and non-O157 STEC in raw beef matrices

Methods: Eighty inoculated raw ground beef, 60 beef trim and 10 finely textured beef (FTB) samples were analyzed. IMS was performed on an aliquot of all samples by the PickPen device and the OctoMACS. Concentrated samples were plated according to MLG 5.06 (E. coli O157:H7) and MLG 5B.05 (non-O157 STEC). 

Results: A total of 150 inoculated samples were tested.  One hundred twenty-five samples were confirmed positive with both the PickPen and OctoMACS columns. For the USDA MLG 5.06 reference method, 30 out of 30 samples confirmed positive for E. coli O157:H7 using both PickPen and OctoMACS methods.  For the Assurance GDS MPX method, 13 out of 25 Ground Beef samples and 17 out of 25 Beef Trim samples confirmed positive for non-O157 STEC using both PickPen and OctoMACS IMS methods. For the USDA MLG 5B.05 reference method, 12 out of 25 Ground Beef samples and 14 out of 25 Beef Trim samples confirmed positive for non-O157 STEC using both PickPen and OctoMACS IMS methods. 

Significance: This validation study demonstrates the equivalence of the IMS concentration when either the Assurance GDS PickPen device or the OctoMACS paramagnetic columns is used for immunomagnetic separation of E. coli O157:H7 and non-O157 STEC from enriched samples.