SF6016 - Evaluation of Immunoassay Based Kits with High Sensitivity and Specificity for Rapid Detection of E. coli O157:H7 in Foods

| Food Safety Research Program - Project Summaries 2002 Index Page |

Researcher:

Dr. Joseph Odumeru, Laboratory Services Div., University of Guelph

Objectives:

1. To evaluate the Immunocard STAT! E. coli 0157:H7 detection kit (Meridian Diagnostics) for the detection of E. coli 0157:H7 from various food products including: raw ground beef, milk, cider, alfalfa sprouts and cheese.
   

2. To establish a protocol for the screening of E. coli 0157:H7 using the above detection kit by investigating the use of Immunomagnetic separation technology and commercial selective agars for the rapid isolation of E. coli 0157:H7 from low level contaminated samples.

Expected Benefits:

• The ability of assays to specifically detect E. coli 0157:H7 within 24 hours of testing would provide a rapid turn around time for reporting test results as well as reducing the occurrence of false positives and misidentification, while maintaining a high sensitivity of detection.

Summary of Research Results:

A commercial immunoassay detection kit, the ImmunocardSTAT! E. coli 0l57:H7 (Meridian Diagnostics) with reported increased specificity for the detection of Escherichia coli 0157:H7 was evaluated for its performance in the detection of Enterohaemorrhagic E. coli (EHEC) 0157 in various food matrices in relation to other commercial detection kits: Eclipse E. coli 0157:H7 (Eichrom Technologies Inc.), RapidChek E.coli Ol57 (Strategic Diagnostics Inc.), and Reveal E. coli 0157 (Neogen Inc.).

After testing 70 pure cultures, including: 19 E. coli 0157:H7 of phage types commonly implicated in food-related outbreaks, 3 E. coli 0157: non- H7, 11 other E. coli non-0157 strains, and 37 non - E. coli strains from 17 genera, all four test kits had a 100% sensitivity rate for detecting EHEC 0157. Specificity rates were estimated at 94.2% for the Immunocard STAT! 0157:H7 kit, whereas other kits had 88.4% specificity. The limits of detection were estimated at 104 - 105 CFU/mL for the Reveal 0157 and RapidChek 0157 test kits, 105 - 106 CFU/mL for the Immunocard STAT! 0157:H7 test kit, and 106 - 107 CFU/mL for the Eclipse 0157:H7 test kit.

Inoculation tests with nalidixic acid resistant E.coli 0157:H7 strains in various food matrices including ground beef, unpasteurized apple cider, alfalfa sprouts, and cheese revealed that less than one E.coli 0157:H7 cell per g or mL of sample could be detected following enrichment procedures. Detection rates of 100% were achieved when samples where enriched in modified EC broth supplemented with 20 mg/L Novobiocin at 36 ± 1ºC. This study indicates that the Immunocard STAT! 0157:H7 detection kit is suitable for pre-screening EHEC 0157 present in low levels in foods. It is recommended that positive samples tested by this assay should be confirmed by cultural methods allowing further isolate characterization.