Automated immunomagnetic separation for the detection of Escherichia coli O157:H7 from spinach

Authors: CHEN, JING - Shanghai Jiaotong University; SHI, XIANMING - Shanghai Jiaotong University; Gehring, Andrew; Paoli, George

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2014
Publication Date: 3/28/2014
Citation: Chen, J., Shi, X., Gehring, A.G., Paoli, G. 2014. Automated immunomagnetic separation of Escherichia coli O157:H7 from spinach. Food Control. 179:33-37.

Interpretive Summary: Escherichia coli O157:H7 is an important foodborne pathogenic bacterium resulting in more than 96,000 illnesses, 3200 hospitalizations, and, 30 deaths each year in the United States. Infection is most often associated with the consumption of undercooked ground beef, but the incidence of infection associated with consumption of leafy greens and other produce has been increasing. To prevent the distribution and consumption of contaminated foods, food producers and regulatory agencies need rapid, specific and sensitive methods to detect E. coli O157:H7. When present in foods, E. coli O157 is typically at very low levels. Therefore, microbiologists typically grow food samples in culture media to increase the number of E. coli O157:H7 to a detectable level. Another method to concentrate the bacterium is to use tiny magnetic beads that specifically bind the E. coli O157:H7 and then pull the magnetic beads with the captured bacteria onto a magnet. A few commercial instruments have been developed to automate this process of “immunomagnetic separation” (also called IMS) for capture and concentration of deadly bacteria from food. We report here the comparison of three methods for IMS concentration and detection of E. coli O157:H7 from spinach. One of the methods was found to be superior to the other in that it captured more of the bacteria. This could allow more sensitive detection of E. coli from foods or could be used to reduce the time needed for culturing the bacterium; thus reducing the time-to-result.

Technical Abstract: Escherichia coli O157:H7 is a major cause of foodborne illness and methods for rapid and sensitive detection of this deadly pathogen are needed to protect consumers. The use of immunomagnetic separation (IMS) for the capture and concentration of foodborne pathogens has been gaining popularity, in part because of the introduction of automated and high throughput IMS instrumentation. Three methods for automated IMS, the Kingfisher mL, the Pathatrix Auto, and the Pathatrix Ultra, were compared using microbiological detection of E. coli O157:H7 from buffered peptone water (BPW), in the presence of background microbial flora derived from spinach leaves, and from culture enrichments from artificially contaminated spinach leaves. The average efficiencies of capture of E. coli O157:H7 using the three methods were 32.1%, 3.68%, and 1.31%, respectively, in BPW; 43.4%, 8.81%, 2.88%, respectively, in the presence of spinach microbial flora; and 63.0%, 6.98%, and 6.29%, respectively, from artificially contaminated spinach. Despite the large differences between the IMS capture efficiencies between the KingFisher and two Pathatrix methods, all three methods allowed the detection of E. coli O157:H7 from artificially contaminate spinach after 4-6 h of culture enrichment of samples inoculated with relatively high (25 cfu/sample) and low (1 cfu/sample) levels of the pathogen. The differences in capture efficiency were compensated for by the differences in sample volume used by the KingFisher mL (1 mL), Pathatrix Auto (50 mL) and Pathatrix Ultra (250 mL) instruments. Thus, despite the reduced capture efficiencies observed for the Pathatrix method, the large increase in sample volume results in a greater number of cells for downstream detection.