Satisfactory microbial limits for a food sample will be dependent on the food preparation, conditions (raw, ready-to-eat, and frozen, refrigerated, shelf stable) and commodity type (e.g., dairy, meat, etc.) in relation to a specific analysis. Refer to Health Canada’s Health Products and Food Branch (HPFB).
Standards and Guidelines for Microbiological Safety of Food - An Interpretive Summary1 for food commodity type details.
The tables below describe the reporting limit and unsatisfactory level for ready-to- eat foods for indicator bacteria and foodborne pathogens according to Health Canada2, and physicochemical testing available at PHO Laboratory. If a board of health would like further interpretation on food results, contact PHO Laboratory Customer Service Centre at 416-235-6556 or toll free 1-877-604-4567, and provide the sample identification number.
||Reporting Limit (CFU/g)a
||Unsatisfactory Level (CFU/g)a, c
|Aerobic Colony Count
||< 1,000 to > 200,000
Category 1: ≥ 105,
Category 2: ≥ 107,
Category 3: N/A
|| < 3 to > 1,100 b
||< 3 to > 1,100 b
|Total gram negative
|| < 1,000 to > 200,000
||≥ 10 4 d
|Yeast and mould
|| < 10 to > 200,000
|| No reportable limit available
a CFU (colony forming units)
b MPN (most probable number) is used for this test method
c Microbial guidelines as per Health Canada
d Microbial guidelines as per Alberta Health Services 3
Unsatisfactory levels of indicator bacteria indicate improper food preparation, handling, storage or holding conditions, temperature abuse, and/or sanitation. Refer to specific test details below for more information.
Aerobic Colony Count (ACC): It is reasonable to expect properly prepared and handled ready-to-eat processed or cooked foods, where no additional food handling was required after food preparation, to have an ACC of < 104 CFU per gram. An ACC of > 105 CFU per gram is usually evidence of post processing temperature abuse, inadequate cooking or improper storage conditions. ACC cannot be applied to raw, uncooked, unprocessed foods (e.g., fruits or vegetables), cultured or fermented products (e.g., cheese, yogurt or salami, etc.) since these foods are known and expected to have naturally occurring microbial flora. There are three categories of ACC listed in the table above, which are based on food type and the processing/handling the food has undergone.
Category 1 – cooked foods that do not require handling or processing; i.e., soups, bread, quiche, cooked meat, fish & seafood, vegetables, etc.
Category 2 – cooked foods that require further handling prior to or during the preparation of the final product; i.e., hot dogs, sandwiches, burgers, etc.
Category 3 – foods that have a high ACC due to the normal microbial flora associated; i.e., pitas, potato or pasta salad, salad rolls, fresh fruits, raw vegetables, cheese, yogurt, deli meats, etc.
Total Coliform: Presence of coliforms in a processed, cooked, ready-to-eat food is indicative of inadequate processing or post processing contamination resulting from poor handling of the product. A satisfactory limit cannot be applied to uncooked or raw foods such as salads and salad ingredients, raw fruits and vegetables, raw meats as well as some fermented foods, etc., since coliforms are regularly found in and/or on these foods.4
Escherichia coli: The presence of Escherichia coli in food is indicative of direct or indirect contamination of the food product with fecal material, thus, enteric pathogens may also be present. The presence may be indicative of inadequate processing, post processing contamination and poor sanitation.
Total gram negative: 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.
Yeast and mould: The presence of yeast and moulds can cause various degrees of deterioration and decomposition of food, resulting in abnormal odours, flavours and colours. Both yeast and mould can also be added intentionally to a product for a desirable flavour such as mould for blue and brie cheeses and yeast for beer, ciders and wines.
a CFU (colony forming units)
b Microbial guidelines as per Health Canada
Foodborne pathogens should not be detected from a ready-to-eat food and would indicate improper food preparation, poor handling, inadequate sanitation practices or possible contamination from a positive food source or an ill food handler. Appendix C: Major Foodborne Diseases: General Features provide additional information regarding the organisms incubation period, clinical symptoms, mode of transmission and associated foods.
pH: The pH is a function of the hydrogen ion concentration in the food and is a measure of food acidity and alkalinity, which varies with food type. pH is measured on a scale of 1 to 14, with 7 being neutral, lower numbers indicating greater acidity and higher numbers indicating greater alkalinity. pH is just one factor that influences bacterial growth, and can interact with the following to inhibit growth of pathogens and other organisms: water activity (aw), salt, redox potential, preservatives and temperature. As the pH decreases, a lower temperature is needed to inactivate microbes.5 Foods with an equilibrium pH ≤ 3.7 will not support the growth of bacterial foodborne pathogens, regardless of the aw. However, if the pH of the food (jarred/canned products) is ≤ 4.6, microorganisms are inhibited providing the aw is ≤ 0.85. According to Public Health Ontario’s Home Canning Literature Review, June 2014, a hermetically sealed acidic canned or jarred food with an equilibrium pH ≤ 4.6 that has gone through sufficient heat treatment to eliminate vegetative microorganisms (bacteria, yeasts and molds), will not support the germination and growth of botulinum spores and production of the toxin.
Phosphatase: The enzyme alkaline phosphatase (ALP) is associated with the cream or fat globules of raw milks. It is inactivated below the detection limit of conventional methods following complete pasteurization. The detection of residual alkaline phosphatase indicates a reduction in pasteurization temperature of at least 1.5°C, a 5 minute reduction in holding time, or the presence of ≥ 0.3% raw milk. Since ALP is more heat stable than most pathogens (which may be present in milk), it is used as an indicator of pasteurization; however, a negative ALP test does not guarantee that the product is pathogen free.6
Water activity (aw): The availability of water for microbial, enzymatic or chemical activity determines the shelf life of foods. This water availability is measured as water activity (aw). Water activity is the ratio of water vapor pressure of the food substrate to the vapor pressure of pure water at the same temperature. Water activity is measured on a scale of 0 to 1; pure water has an aw of 1.00 and the aw of a completely dehydrated food is 0.00. For most foods to be considered safe to store at room temperature, they should have an aw ≤ 0.85. Bacterial foodborne pathogens are inhibited at this aw; however, for those microorganisms that can cause spoilage (e.g., yeasts and moulds), the aw should be < 0.60 to prevent food spoilage by inhibiting growth of these organisms.7