Comparison of immunomagnetic separation beads for detection of six Non-O157:H7 shiga toxin-producing Escherichia coli serogroups in different matrices

Authors: KRAFT, AUTUMN - North Dakota State University; LACHER, DAVID - Us Food & Drug Administration (FDA); Shelver, Weilin; SHERWOOD, JULIE - North Dakota State University; BERGHOLZ, TERESA - North Dakota State University

Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2017
Publication Date: 9/1/2017
Citation: Kraft, A.L., Lacher, D.W., Shelver, W.L., Sherwood, J.S., Bergholz, T.M. 2017. Comparison of immunomagnetic separation beads for detection of six non-O157 Shiga toxin-producing Escherichia coli serogroups in different matrices. Letters in Applied Microbiology. 65(3):213-219. https://doi.org/10.1111/lam.12771.
DOI: https://doi.org/10.1111/lam.12771

Interpretive Summary: Shiga toxin-producing E. coli (STEC), particularly E. coli O157:H7 is one of the major causes of foodborne illnesses in humans. An increase in infections produced by non-O157:H7 STECs has prompted the US Department of Agriculture, Food Safety and Inspection Service to regulate the presence of so called “big-six” STECs that cause the majority of illnesses as illegal substance present in foods. An important step in preventing STEC-associated foodborne outbreaks is detecting these pathogens in foods before they reach the consumer. In this paper, a technique called immunomagnetic separation (IMS) was chosen for assessment of its ability to detect non-O157 STECs from a mixture of bacteria in sterilized phosphate buffered saline (PBS) and cattle feces as well as non-sterilized cattle feces, ground beef and lettuce. In addition, the performance of IMS beads from three manufacturers were compared. The rate of correct identification varied with different bacteria group, IMS bead manufacturer, and media tested, ranging from 100% correct identification in PBS to none in lettuce and ground beef. More research is needed for IMS to be able to accurately isolate STECs from a variety of foods.

Technical Abstract: A concern in public health and food safety in the United States involves the need to accurately and efficiently detect Shiga toxin producing Escherichia coli O26, O45, O103, O111, O121, and O145 which have caused outbreaks on numerous occasions. The detection of these organisms is challenging because of their similarity and the presence of other microorganisms in a variety of complex matrices. Immunomagnetic separation (IMS) used in conjunction with culture based methods has been a useful technique in the detection of pathogens, however the previous explorations have not systematically examined a number of the complexities needed for real world applications. Samples of sterile phosphate buffered saline (PBS), sterile and non-sterile feces, ground beef, and lettuce were inoculated with a 1cfu/ml concentration mixture of isolates representing the six serogroups to assess IMS’ ability to isolate correct serogroup from different matrices and a mixture of STECs. After a 6h incubation at 37'C, the samples were mixed with three different commercially-available IMS beads and plated on eosin methylene blue agar (EMB). Three suspect E. coli colonies were selected from the EMB and multiplex PCR was used to determine the serogroup. The rate of correct identification varied with the serogroup, IMS bead manufacturer, and media ranging from 100% correct identification in PBS to 0% in lettuce and ground beef. More research is needed to optimize the use of this technique.