Total Gram Negative Count – Food
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Food Bacteriology1 |
Food – indicate if part of a meal, control or follow up |
25 grams |
Sterile plastic bag with round wire closure. |
Submission and Collection Notes
Test selection is completed by the laboratory and is based on the information provided on the requisition. Specific analyses may be requested using the ‘Comments’ section of the requisition.
Special Instructions
For sampling, follow the instructions found in Public Health Inspector’s Guide to Environmental Microbiology Laboratory Testing.
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.
- DO NOT SHIP WITH CLINICAL SPECIMENS. 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 ice 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 Frequency and Turnaround Time (TAT)
The total gram negative count is performed Monday to Saturday.
Turnaround time is up to 7 days.
The total gram negative count is determined by culture using the spread plate method with agar plates that are selective for gram negative bacteria. (Public Health Ontario Laboratory Method)
Interpretation
Total gram negative (TGN) count has the same significance as presence of coliforms. Elevated TGN count should not be detected in cooked or processed ready-to-eat foods. Absence of gram negative organisms in a food sample is another indicator of food safety.
Reporting
Results are reported to the submitting health unit as indicated on the requisition, when all analyses are completed.
Food samples that show the presence of bacteria capable of causing food-borne illness are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.
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