Investigation of systems for detection of enterohemorrhagic Escherichia coli contamination in foods

Enterohemorrhagic Escherichia coli (EHEC) has been recognized as a human pathogen since 1982. Contaminated ground beef is the food source most implicated in this type of infection.;A composite sampling plan is essential in obtaining statistically valid results for detecting bacterial pathogens in food products. The sensitivity of a rapid E. coli O157:H7 detection assay with 375 g composite samples was evaluated. The assay combined an immunomagnetic separation technique and enzyme-linked immunosorbent assay (IMS/ELISA) system. By analyzing raw ground beef inoculated with low levels of E. coli O157:H7, the sensitivity of the IMS/ELISA was determined to be 10;Target/competitor ratio in the food sample is a key factor affecting the performance of rapid microbial detection systems. High background flora may prevent the target organism growth to the assay detection limit which leads to false negative results. A model system was developed in this study by inoculating antibiotic resistant E. coli O157:H7 (the target organism) and antibiotic sensitive non-pathogenic E. coli (the competitor organism) into trypticase soy broth with acriflavine (TSB+a), and modified EC with or without novobiocin (mEC+n and mEC). TSB+a performed better than mEC in supporting growth and subsequent detection of E. coli O157:H7 with the target/competitor ratio of 1/10;Verotoxins produced by EHEC is one of the virulence factors for hemolytic uremic syndrome caused by EHEC infection. An ELISA for detecting verotoxin producing organisms in food samples was evaluated. EHEC cultures (E. coli O157:H7, E. coli O46:H38, and E. coli O26:H11) were detected by the ELISA when 10...