Ambient temperature

Ambient is the natural temperature of the air in a room that has not been heated or cooled


Aw stands for water activity. In food safety, aw is a measure of how much water within a food is available to micro-organisms (and is not the moisture content). Aw values depend on the salt and the sugar content of the food (these can prevent water being available), the amount of water that would exist within the food and the amount that would exist as vapour if the food was placed in a sealed container. Many factors can change Aw, including temperature.

The range of values for water activity is always between 0 and 1. A value of 1 is pure water. In general, bacteria need a high water activity value (at least 0.9) to multiply in food.


Biotypes are closely related strains of bacteria. Typically, the strains originally came from a common ancestor. Bacteria evolve to become better suited to their environment and the evolutionary changes will differ in different places, resulting in a series of closely related strains or biotypes.

Biofilms and planktonic L. monocytogenesL. monocytogenes is known to exist in two forms:  as planktonic cells (i.e. as free-swimming, mobile single cells) or as a sessile biofilm (i.e. as part of a group of individual cells living in close proximity and enmeshed within a web of protective polymers).  Planktonic forms of bacteria are susceptible to most mainstream cleaning and sanitization agents and so can be effectively controlled.  However, as a biofilm, L. monocytogenes can be very resistant to the action of cleaners and sanitisers.  Compared with planktonic forms, biofilm L. monocytogenes requires 10-20 times more chemical to achieve the same degree of kill.  Different cleaning and sanitation strategies such as prolonged scrubbing are therefore required for the removal of L. monocytogenes biofilms.  
cfu/cm2 CFU stands for colony forming unit. A cfu is a colony of micro-organisms which usually grows from the multiplication of a single cell. A cfu is a measure of the number of micro-organisms in a sample of food. 
Challenge testingChallenge testing is when a sample of food is deliberately contaminated with a lab-grown bacterium such as L. monocytogenes to see what will happen to the numbers of the pathogen over time. Commonly it is used to help establish shelf lives for food.
Control point (CP), Operational Prerequisite programme (oPRP) or secondary control point (SCP) Three terms that mean broadly the same thing and are used interchangeably by a number of food safety schemes.  The term is usually described as a processing practice (e. g. the use of hot water sterilisers for gutting knives) or a supply condition (e.g. raw fish supplied should only be from a certain source) that does not critically control the L. monocytogenes hazard, but reduces the likelihood of the hazard occurring.
CorrelationCorrelation describes the relationship between two sets of numbers. If the numbers change in a predictable way, that is, if one set increases and the other also tends to increase, then they are positively correlated. On the other hand, if one set tends to decrease as the other increases, then they are negatively correlated. If there is no obvious relationship, then the two sets of numbers are not correlated.
Criterion ACriterion is a standard set of conditions that are applied to foods in order for the product to be deemed acceptable for consumption. For example, for cold smoked salmon, it is important that the fish are cured properly so that the product tastes good. The criterion for effective curing could be laboratory testing of the fish to find out how much salt it contained. Only the fish with above a certain level of salt would pass the criterion.
DNA fingerprinting methodDNA fingerprinting involves the examination of an organism’s genetic material to produce a reproducible genomic pattern that is unique to the organism. 
FomitesA fomite is any object that is capable of transferring contamination from one place to another. An example of a fomite is a door handle. If one person with contaminated hands touched the handle, cross-contamination to other people using the handle could occur.
FrequencyThe number of occurrences of an event over a period of time. For example a clock that chimes on the half hour and the hour has a frequency of two chimes per hour.
GHPGHP stands for good hygienic practice. It is a particular way of handling and processing food so that it does not become contaminated. GHP can be applied to a wide range of activities such as the adequacy of the refrigeration of food; the use of gloves, aprons and hair nets; the regular cleaning of the plant environment and the control of insects and vermin within and around the processing environment.
Gill gas-exchange surfacesThe gill gas-exchange surfaces are the part of fishes’ gills that remove oxygen from water.
HypothesisedAn unconfirmed explanation for an observation or scientific problem that can be confirmed by undertaking experimental investigation.
Impaction samplerAn impaction sampler is a piece of equipment that sucks in a measured volume of air and measures the numbers of bacteria contained within that air.
Indigenous micro-organismsIndigenous micro-organisms are those which are present in a place (e.g. soil, water) naturally.
Inoculated Inoculation is the act of deliberately transferring bacterial cells from one place to another. For example the transfer of L. monocytogenes cells to a product so you can see how well they grow in that product.
Intervention A modification or additional treatment introduced into a food manufacture process that helps to control a food safety hazard.
Isolation In food microbiology, an isolation is when food is tested and found to contain a particular micro-organism. For example if fish was tested to see if it contained Salmonella, and the result was that it did, the laboratory would report an isolation and the Salmonella would be called the isolate.
L. monocytogenes Listeria monocytogenes is a bacterium that causes an infection named listeriosis in humans. The elderly, pregnant women and immunocompromised people are particularly at risk from L. monocytogenes infections. The symptoms are very similar to meningitis. L. monocytogenes is routinely isolated from seafoods that have not been cooked such as cold smoked fish.
Lab-cultured cocktailA mixture of different species or strains of micro-organisms grown together in sterile water containing nutrients.
Lag time/Lag phaseWhen bacteria encounter a new environment, it takes them time to determine what nutrients are available to them. Once that information is available, the cells switch on what they require to make use of the nutrients and grow in the new place. Although the cells are busy, it looks like nothing is happening and thus the delay is called the lag phase before growth.
Lipid Lipid is a general name for a group of closely related molecules, which include fats, waxes and sterols such as cholesterol.
Log reductionA log reduction is a 10 times reduction. For example a log reduction of 1000 is 100.
Lysozymes Lysozymes are natural chemicals found in egg whites that can damage and kill some types of bacteria, including L. monocytogenes.
Multivariate analyses Multivariate analyses are a specialist branch of mathematics/statistics. In essence it is a way of trying to find out how things interact and are related to each other. For example, if lots of different food processing premises were surveyed and data was collected describing their manufacturing processes (including microbiological testing), it would be possible to use multivariate analyses to identify what stages of each process were beneficial in terms of food safety and how each of the different stages of a single process interacted to produce the final bacterial populations on food.
Naturally contaminatedFood contaminants are any harmful substances unintentionally added to food. These substances include micro-organisms and chemicals, some of which can be from natural sources.
NichesNiches are places where groups of bacteria can become established and colonise. Examples of niches are floor drains, cracks in equipment casings, and the inside of chiller door seals.
Persistent strainsPersistent strains of bacteria are those that have an ability to colonise food processing plant environments (e.g. floor drains), to resist cleaning and sanitation and to continuously contaminate final product, albeit at a low level.
pH pH is a measurement of the amount of acid that a substance (e.g. food) contains. pH is a chemical property of a substance. pH is measured on a scale with values between 1 and 14.
Physicochemical Physicochemical relates to the physical or chemical properties of a substance. Examples of physical properties are the weight of an object, its hardness and its size. Chemical properties relate to things like the amount of salt, sugar or fat that a food contains.
Predictions validated against real world observations When mathematicians try to describe a system such as a food manufacture process, they check the validity of their work by comparing what happens in real life with the results forecast by their models.
Predictive microbiological (mathematical) modelling and critical survival and growth characteristics Modelling is a term used by specialist mathematicians to predict how things will behave. In the food industry, mathematical modelling is used to predict how bacteria will behave within a food. The process takes into account the properties of the food – for example, the salt, sugar and fat content of the food – and tries to predict if bacteria will survive, grow or die off if they contaminate a particular batch of food. Critical survival is a point where a food’s formulation allows bacterial survival in food. Growth is a point when bacteria are able to multiply in food.
Prerequisite programme (PRP)The basic supply and processing practices that are necessary to maintain a hygienic environment throughout the food chain.  A PRP describes the conditions that are required for the manufacture and packaging of food that is safe for human consumption.  Processor PRPs can extend into both the supply chain and their customer’s distribution chains.
Prevalence Prevalence is the percentage of a population that have a particular trait. For example, if the number of people with red hair was 5 within 100 people tested, the prevalence of red hair would be 5%. In the food industry the prevalence is used to describe the degree of contamination of foods by potential pathogens such as L. monocytogenes.
Robust replication In order for the results of an experiment to stand up to scrutiny, scientists repeat an experiment several times. Replication refers to repeatedly doing the same experiment over and over, using the same experimental conditions. Robust replication occurs when the number of repeats reaches a point where the result is considered reliable and reproducible.
Routine surveillancePeriodically, the government run routine checks of the food offered for sale in retail outlets to ensure it is safe. The process of visiting stores, buying food and testing it in a laboratory is called routine surveillance. 
Salt content The salt content is a measure of the amount of salt contained within a food.
Sensitive predictorA sensitive predictor is information (e.g. a set of data) that reliably forecasts the status of another set of data. For example being male, obese and older than 50 is a sensitive predictor for a patient having diabetes.
Settle plates Settle plates are small dishes containing nutrients in jelly that are placed to catch and count micro-organisms that settle out of the air.
Sporadic A sporadic event is one that occurs unpredictably and rarely.
Strains A strain is a genetic variant or a subtype of a bacterium. For example, each bacterium such as L. monocytogenes has many variants that are all slightly different to each other but evolved from a common ancestor and share the vast majority of their genes.
Sub-lethal A sub-lethal injury is one that almost, but does not quite, kill a micro-organism. Cells that are sub-lethally injured can recover given favourable conditions.
Substantiating The provision of evidence that supports a viewpoint or opinion.
Verification Verification is the process of establishing the validity or truth of something. In the food industry, the term usually applies to a check that something has happened the way that it should. For example, after cleaning, a visual inspection could be carried out to make sure there were no food residues remaining on equipment. That would mean the cleaning was verified.