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Types of Contamination

People become ill in one of two ways:

  • Infection -by eating food that contains a living harmful microorganism
  • Intoxication – by eating food that contains a harmful chemical or toxin

In this course we will address three kinds of contaminants that impact food safety:

  • 1. Biological
  • 2. Chemical
  • 3. Physical

1. Biological Contaminants

Biological Contaminants can be divided into four categories:

bacteria image
Virus image
fungi image
parasites image

Biological Toxins

Naturally occur in certain plants, mushrooms, and seafood

Seafood toxins
Produced by pathogens found on certain fish: tuna, bonito, mahi-mahi. A histamine (toxin) is produced when fish is time-temperature abused. Also occurs in certain fish that have consumed the toxin Barracuda, snapper, grouper
Symptoms and onset times will vary.

Ciguatera Toxin and Scrombroid Poisoning are examples of seafood toxins
General symptoms

  • Diarrhea or vomiting
  • Tingling of the extremities
  • Reversal of hot and cold sensations
  • Flushing of the face and/or hives
  • Difficulty breathing
  • Heart palpatations


bacteria image

Bacteria are single-cell microorganisms that are almost everywhere, in air, water, soil, and in and on humans, animals, and plants. They can also survive the harshest of environments from very cold to very hot. Some are beneficial to us and some make us sick or are fatal. They can be seen only by a microscope and can not be seen,tasted or smelled They are of the greatest concern to food service professionals so all the time necessary should be spent to combat them by understanding what conditions favor the growth of pathogenic bacteria and what conditions eliminate or reduce them to a safe level. The right condition for the growth of bacteria and other foodborne microorganisms is remembered by using the acronym

F A T  T O M

Please Note: The six conditions of FAT TOM apply to bacteria. They do not apply to viruses


Bacteria, just like humans and animals require nourishment. In particular they require proteins and carbohydrates.As can be observed, TCS foods generally are high in proteins and carbohydrates
ACIDITY Bacteria grow well in an environment that is slightly or non-acidic, when the Ph value is between 4.6 and 7.5. (see below for an explanation of Ph values)
TEMPERATURE Bacteria grow well in the Temperature Danger Zone (between 41°F and 135°F) They grow even faster in a segment of the Temperature Danger Zone that we will describe as the critical Temperature Danger Zone: between 70°F and 125°F. You will see the critical temperature danger zone come into play in certain processes in a later lesson.
TIME When food is in the Temperature Danger Zone bacteria, on average, will double every twenty minutes. Starting with one bacteria, they will rise to a level of over 1 billion in 10 hours. You can allow TCS foods in the Temperature Danger Zone up to four hours. If it has been in the temperature danger Zone for 4 hours or longer, it must be thrown out. Bacteria have multiplied to harmful levels. The time TCS food spends in the Temperature Danger Zone is also cumulative. Each amount of time it spends in the Temperature Danger Zone cannot add up to 4 hours or more.
Oxygen Most, but not all, bacteria require oxygen for growth. Aerobic bacteria grow in the prescence of oxygen while anaerobic bacteria will grow without oxygen
MOISTURE Bacteria require a high level of moisture to grow and multiply. Moisture levels are measured using the Water Activity ( Aw ) Scale. We can generally define Water Activity (Aw) as an indication of the amount of Free Water in a food. The scale runs between 0 and 1 with pure distilled water having a Aw value of 1 which means it is 100% water. Bacteria grow well in a food with a water activity value of .85 or higher. So what does free water in a food mean? If you add salt to a glass of water that has a water activity of 1 it will lower the water activity level. Some water molecules in the water will bind to the salt molecules thus reducing the water activity level. Those water molecules that bind to the salt molecules are no longer available for bacteria (no longer “free”) Adding enough salt will lower the water activity to below .85 thus restricting/eliminating bacterial growth. As known, man has been using salt as a means of preserving food for thousands of years.


The Ph Scale

The amount of acid in a food is measured using the Ph Scale. The scale runs from 0 to 14 with pure distilled water having a Ph value of 7 indicating that it is neither acidic or alkaline. It is totally neutral. As the scale progresses toward 0 the acid level increases. For example, a Ph value of 6.5 means the food is ever so slightly acidic; whereas, a food with a Ph value of zero indictes it is 100% acid. Bacteria grow well in a food that is slightly or non-acidic. With a Ph value between 4.6 and 7.5 as shown in the diagram below.

Ph Scale image

As outlined in the following chart, the amount of acid in a product increases tenfold for each Ph value. A change in Ph value from 7 to 6 shows a tenfold increase in the amount of acid in a product. A change in Ph value from 6 to 5 also shows a tenfold increase in the amount of acid in a product and so forth. As you can observe, changes between the lower Ph values show a dramatic change in the amount of acid.

Ph value of certain foods chart

Time and Temperature

Bacteria grow best in the Temperature Danger Zone. At those temperatures some bacteria can double their population every 20 minutes. With each 10°F temperature drop below the Temperature Danger Zone, the bacterial growth slows down, taking twice the time to double the population. As the temperature rises above the Temperature Danger Zone bacteria stop growing and start dying. Foods cooked to the required minimum internal temperature will kill bacteria.

TCS foods grow bacteria if the temperature is in the Temperature Danger Zone). Foods on a warming table kept above 135°F stays safe and foods kept at refrigerator temperatures (41°F) or below also stay safe, at least for a few days.

Time goes with temperature as it takes time for bacteria to reproduce. The food safety rules allow up to 4 hours for TCS foods to be in the 41°F – 135°F temperature range. This 4 hours includes all the times the food is brought into the Temperature Danger Zone, like each time you reheat leftovers.

Some especially vulnerable foods for the time rule are leftovers and partially cooked foods—they need to be cooled quickly. Leftovers from a buffet or picnic, or a large pot of beans that is allowed to sit, are prime candidates for foodborne illness.

In summation, the way to control bacteria growth in a foodservice establishment is to control Time and Temperature. Time and Temperature are the two conditions that can be controlled in a foodservice establishment. The other four conditions are too complex to control.

Major Bacteria that Cause Foodborne Illness

The FDA has identificed seven types of bacteria that cause severe illness and are highly contagious