MID was defined as the number of microorganisms ingested (the dose) from which a pathology is observed in the consumer.
This may be calculated using the following formula: where: This formulation has served as a basis for reasoning to establish the maximum concentrations permitted by the microbiological regulatory criteria intended to protect the health of consumers.
The concept of a dose-response relationship dates back to as 1493 but its modern usage reaches to the 20th century,[3][4] as quantitative risk assessment matured as a discipline within the field of food safety.
An infectious bacterium in a food can cause various effects, such as diarrhea, vomiting, sepsis, meningitis, Guillain-Barré syndrome, and death.
The existence of this relation has a first important consequence: the proportionality factor, symbolized by the letter r, corresponds precisely to the probability of the effect considered when the dose is equal to one bacterial cell.
As a result, the minimum infective dose is exactly equal to one bacterial cell, deviating from the traditional notion of the MID.
These are values of D1 (dose causing the effect considered in 1% of consumers exposed to the hazard):[citation needed] These examples highlight two important things:[according to whom?]
Some synthesize a toxin only when their concentration in the food before ingestion exceeds a threshold, such as Staphylococcus aureus and Bacillus cereus.