Isolation of Escherichia coli O157:H7/NM from foods and environmental surface samples
Background: Escherichia coli is a very common harmless bacterium found in the intestine of many animals and humans. However, a small number of E. coli have different O and H antigens, and this confers them the capacity to attach to the interior of different organs and produce potent enterotoxins which can cause serious enteric diseases. From those enteric E. coli pathogens one of the most common is E. coli O157:H7. It is considered enterohemorrhagic and can cause bloody diarrhea, colitis and hemolytic-uremic syndrome (HUS), which can lead to kidney failure and death. Children and elderly are particularly at risk. About 10% of children under 10yrs old with a E coli O157/H7 infection will develop HUS. Fatality rates for HUS can reach between 6 and 31%.
E. coli O157:H7 is a recognized foodborne pathogen that has been found in raw beef (especially ground beef), unpasteurized milk and dairy products, apple juice, contaminated water and vegetables. It can cause serious and sometimes fatal illness at a very low infection dose (as few as 10 organisms). The pathogen is often difficult to differentiate from other less pathogenic E. coli with traditional culture methods, especially where low levels of the target must be isolated from high levels of competing background flora.
This method allows to determine the presence of E. coli O157:H7 from food and environmental samples (swabs). Following enrichment, an immunomagnetic separation allows to obtain purified E. coli O157:H7 extracts, which are then isolated on plates and tested using different biochemical tests. This method is also used to confirm positive results from BAX-PCR testing.
Method: Health Canada (MFHPB-10)
Turn Around time: 2-3 Business Days
Reported Results: positive or negative for E. coli O157:H7 for food. (Samples or swabs)
SPECIMEN REQUIREMENTS
Container/Kit: Submit 250 grams of food in a sterile plastic sample bag with round wire closure or swab.
Collection information: See Section Sampling under Food Sampling.
Requisition: Complete all fields of the form. See section Forms under Microbiology Sample Sheet.
Sterile bag: See section Form under Requisition for Containers and Supplies.
Preparation prior to transport: Keep refrigerated or frozen.
Shipping Instructions:
- Ship all foods in containers with hard walls and lids secured in the closed position.
- Shipping containers must be labelled with the submitting organization, unique identifier and contents e.g. FOOD SAMPLES on the outside of the container.
- Shipping containers used for food samples should be dedicated to food samples and not be used for other types of environmental samples.
- Ship dry foods and other shelf stable foods at ambient temperature in a closed container.
- Ship frozen foods in an insulated container with sufficient dry packs to maintain the frozen state.
- Ship perishable foods in an insulated container with sufficient cold packs to maintain a temperature as close to 4°C as possible. If ice is used, contain the ice in a manner that does not allow water contact with the samples.
- Submit all food samples to the laboratory as soon as possible
TEST INFORMATION
The presence of Escherichia coli O157:H7 is detected by culturing food in non-selective enrichment broth followed by Immunomagnetic Separation (IMS) and isolation on selective agar plates with subsequent biochemical and serological identification.
Escherichia coli O157:H7 should be absent.