ServSafe Essentials
danger zone: The temperature range between 41°F
- and 140°F (5°C and 60°C) within which most foodborne bacteria grow and
reproduce.
Water activity: The amount of moisture available in food for
microorganisms to grow. Potentially hazardous food has water activity
(aw) values of .85 or above.
Mold: A type of fungus that causes food spoilage. Some molds produce
toxins that can cause foodborne illness.
Yeast: A type of fungus that causes food spoilage.
Foodborne infection: The result of a person eating food containing
pathogens, which then grow in the intestines and cause illness. Typically,
symptoms of a foodborne infection do not appear immediately.
Foodborne intoxication: The result of a person eating food
containing toxins (poisons) that cause an illness. The toxins may have
been produced by pathogens found on the food or may be the result of a
chemical contamination. The toxins could also come from a plant or
animal that was eaten. Typically, symptoms of food borne intoxication
appear quickly, within a few hours.
Foodborne toxin-mediated infection: The result of a person
'?ating food containing pathogens, which then produce illness-causing
- toxins in the intestines.
INTRODUCTION
Jn the previous section, you learned that foodborne microorganisms pose
the greatest threat to food safety, and that disease-causing microorganisms
are responsible for the majority of foodborne-illness outbreaks. In this
section, you will learn about the microorganisms that cause foodborne illness,
as well as conditions they require in order to grow. When you understand
these conditions, you will begin to see how the growth of microorganisms
can be controlled, a topic that will be covered in greater detail in
later sections.
Microorganisms are small, living beings that can only be seen with a
microscope. While not all microorganisms cause disease, some do. These are
called pathogens. Eating food contaminated with food borne pathogens or
their toxins is the leading cause of food borne illness.
MICROBIAL CONTAMINANTS
There are four types of microorganisms that can contaminate food and
r'1use foodborne illness: bacteria, viruses, parasites. and fungi.
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The Microworld
These microorganisms can be arranged into two groups: spoilage
microorganisms and pathogens. Mold is a spoilage microorganism. While
its appearance, smell, and taste is not very appetizing, it typically does not
cause illness. Pathogens like Salmonella spp. and the virus that causes
hepatitis A, cause some form of illness when ingested. Unlike spoilage
microorganisms, pathogens cannot be seen, smelled, or tasted in food.
BACTERIA
Of all microorganisms, bacteria are of greatest concern to the manager.
Knowing what bacteria are and understanding the environment in which they
grow is the first step in controlling them.
Bacteria that cause foodborne illness have some basic characteristics:
They are living, single-celled organisms
They may be carried by a variety of means: food, water, humans, or insects
Under favorable conditions, they can reproduce very rapidly
Some can survive freezing
Stationary
Some turn into spores, a change
that protects the bacteria from
unfavorable conditions
Some can cause rood spoilage; others
can cause illness
Some cause illness by producing toxins
as they multiply, die, and break down
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To grow and reproduce, bacteria need:
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e
lag
The appropriate level of acidity (pH)
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Proper temperature
Z
Adequate time
The necessary level of oxygen
Time
Growth Stages of Bacteria
Ample moisture
Bacterial growth can be broken down
into tour progressive stages (phases):
lag, log, stationary, and death.
(See Exhibit 2a.)
ServSafe Essentials
9 Phase
The lag phase is the adjustment period for bacteria, occurring when they
are first introduced to food.
The number of bacteria are stable as they prepare for growth.
Keep the bacteria in the lag phase as long as possible to control growth
and prevent food from becoming unsafe. This is accomplished by
controlling the requirements for growth: time, temperature, moisture,
o min
1 cell
oxygen, and pH.
If these conditions are not controlled, bacteria will enter the next phase
and grow remarkably fast.
20 min
Log Phase
2 cells
Bacteria reproduce by splitting in two. Those in the process of
reproduction are called vegetative microorganisms.
As long as conditions arc favorable, bacteria can grow and multiply very
rapidly, doubling their number as often as every twenty minutes, as
illusrrated in Ey;hibit 2b.
Stationary Phase
Bacteria can continue to grow until nutrients and moisture become scarce,
- or general conditions become unfavorable, at which point they begin to die.
Eventually the population reaches a stationary phase. in which just as
many bacteria are growing as are dying.
Death Phase
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40 min
4 cells
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~
1 hour
8 cells
When the number of bacteria dying exceeds the number growing. the
population declines.
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Staves
and S!WI'i.' Fortiutrion
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Although vegetative bacteria may survive low-and even freezing­
temperatures, they can be killed by high temperatures. Some types of
bacteria, however, have the ability to change into a different form. called
a spore. The spore's thick wall protects the bacteria against unfavorable
conditions, such as high or low temperature, low moisture. and high acidity.
While a spore cannot reproduce, it is capable of turning back into a
vegetative organism when conditions again become favorable. For example,
bacteria in food may form spores when exposed to freezer temperatures,
allowing the bacteria to survive. As the food thaws and conditions improve,
spores can turn back into vegetative cells and begin to grow in the food.
1 hr 20 min
16 cells
.,
10 hrs
over 1 billion cells
Exhibit 2b
Rapid Bacterial Growth
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The Microworld
Since spores are so difficult to destroy, it is important to cook, cool, anc.
reheat food properly.
Information about major foodborne illnesses caused by bacteria, as well as
ways to prevent them, is presented in Exhibit 2e.
T TO/H: W'IJllt Jl1icroorgll1dsUls Need to
Conditions favoring the growth of most food borne microorganisms can
be remembered by the acronym FAT TOM. (See Exhibit 2c.) Each of these
conditions for growth will be explained in more detail in the next
several paragraphs.
UFOOd
To grow, foodborne microorganisms need nutrients, specifically proteins
and carbohydrates. These proteins are commonly found in potentially
hazardous food items, such as meat, poultry, dairy products, and eggs.
(See Page 1-5,)
A
Food
~---
T~
Acidity
Time
Oxygen
Moisture
T
I
Temperature
FAT TOM
Conditions
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the
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The Microworld
~
Moisture
Because most food borne microorganisms require water to grow, they grow
well in moist food.
The amount of moisture available in a food for microorganisms to grow is
called its water activity (aw)' It is measured on a scale from
water having a water activity of 1.0.
°
to 1.0, with
Potentially hazardous food items typically have a water activity of .85
or higher.
Alultiple Barriers for Controlling' the (,Fowth 1{/HicroOl:ga1llsms
FAT TOM is the key to controlling the growth of microorganisms in food.
By putting in place as mallY barriers as possible, you remove conditions that
support bacterial growth. The list below provides some simple steps that,
when combined, can create multiple barriers for ensuring food safety.
Make food more acidic. Add vinegar. lemon juice, lactic acid, or
citric acid.
Raise or lower food temperature. Move food out of the temperature
danger zone by cooking it to the proper temperature, by refrigerating it to
4 n~; (50C) or lower, or by freezing it.
Lower the water activity of food. Dry food by adding sugar. salt, alcohol
or acid. food can also be air- or freeze-dried to remove water.
Limit the amount of time food is in the temperature danger zone.
Prepare food in small batches, as close to service as possible.
VIRUSES
Viruses are the smallest of the microbial contaminants. While a virus
cannot reproduce outside a living cell, once inside a human cell, it will
produce more viruses. Viruses are responsible for several foodborne illnesses,
such as hepatitis A and infections caused by Norwalk virus and rotavirus.
Information about major foodborne illnesses caused by viruses, as well as
ways to prevent them, is provided in Exhibit 2f
Basic Characteristics ofViruses
Viruses share some basic characteristics.
Unlike bacteria, they rely on a living cell to reproduce.
They are not complete cells.
Unlike bacteria, they do not reproduce in food.
Some may survive freezing and cooking.
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The Microworld
They can be transmitted from person to person, from people to food, .
from people to food-contact surfaces.
They usually contaminate food through a foodhandler's improper
personal hygiene.
They can contaminate both food and water supplies.
Practicing good personal hygiene is an important way to prevent the
contamination of food by foodborne viruses. It is especially important to
minimize bare-hand contact with readv-to-eat food.
PARASITES
Parasites share some basic characteristics.
They are living organisms whose survival depends on a host-a person,
animal, or plant on which it lives and from which it takes nourishment.
They grow naturally in many animals-such as pigs, cats, and rodents­ and can be transmitted to humans.
Most arc very small, often microscopic, but larger than bacteria.
They can be killed by proper cooking or freezing.
They pose hazards
to
both food and water.
Information about major foodborne illnesses caused by parasites, as well
ways to prevent them, is presented in Exhibit 2g.
FUNGI
Fungi range in size from microscopic, single-celled organisms to very
large, multicellular organisms. They are found naturally in air, soil, plants,
animals, water, and some foods. Molds, yeasts, and mushrooms are examples
of fungi.
!l101ds
Molds share some basic characteristics.
They spoil food and sometimes cause illness.
They grow under almost any condition, but grow well in sweet, acidic
food with low water activity.
Freezing temperatures prevent or reduce the growth of molds, but do not
destroy them.
Some molds produce toxins called allatoxins.
Although the FDA recommends cutting away any moldy areas in
cheese-at least one inch (2.5 centimeters) around them-to avoid
ServSate Essentials
Unesses caused by mold toxins, throw out all moldy food unless the mold
is a natural part of the food (e.g. cheeses such as Gorgonzola, Bleu, Brie,
and Camembert).
Although mold cells and spores can be killed by heating them, some
toxins are not destroyed by normal cooking methods. Food with molds that
are not a natural part of the product should always be discarded.
Yeasts
Some yeasts are known for their ability to spoil food rapidly. Carbon
dioxide and alcohol are produced as yeast slowly consumes food. Yeast
spoilage may, therefore, produce a smell or taste of alcohol. Yeast may appear
as a pink discoloration or slime and may bubble.
Yeasts are similar to molds in that they grow well in sweet, acidic foods
with low water activity, such as jellies, jams, syrup, honey, and fruit juice.
Food that has been spoiled by yeast should be discarded.
FOODBORNE INFECTION vs.
FOODBORNE INTOXICATION
Foodborne diseases are classified as infections, intoxications, or
roxin-mcdiated infections. Each occurs in a different way.
_ c'oodborne infections result when a person eats food containing pathogens,
which then grow in the intestines and cause illness. Typically, symptoms of a
Ioodborne infection do not appear immediately.
Foodbornc intoxications result when a person eats food containing toxins
that cause illness. The toxin may have been produced by pathogens found
on the food or may be the result of a chemical contamination. The toxin
could also come from a plant or animal that was eaten. Typically,
symptoms of a food borne intoxication appear quickly, within a few hours.
Foodborne toxin-mediated infections result when a person eats food
containing pathogens, which then produce illness-causing toxins in
the intestines.
SUMMARY
Microbial contaminants are responsible for the majority of foodborne
illness. Understanding how microorganisms grow, reproduce, contaminate
food, and infect humans is critical to understanding how to prevent the
food borne illnesses rhev cause.
Of all foodborne microorganisms, bacteria are of greatest concern to the
restaurant and foodservice manager. Under favorable conditions, bacteria can
2
The Microworld
reproduce very rapidly. Although vegetative bacteria may be resistant to
low-even freezing-temperatures, they can be killed by high temperatures,"
such as those reached during cooking. Some types of bacteria, however, have
the ability to form spores, which protect the bacteria from unfavorable
conditions. Since spores are so difficult to destroy, it is important to cook,
cool, and reheat food properly.
The acronym FAT TOM-which stands for Food, Acidity, Time,
Temperature, Oxygen, and Moisture-is the key to controlling the growth
of microorganisms. When put into place, these multiple barriers deny the
microorganisms as many growth-supporting conditions as possible.
Viruses are the smallest of the microbial contaminants. While a virus
cannot reproduce in food, once ingested it will cause illness. Practicing good
personal hygiene and minimizing bare-hand contact with ready-to-eat food
is an important defense against foodborne illness from viruses.
Parasites are organisms that need to live in or on a host organism to survive.
They can live inside many animals humans eat, such as cows, chickens, hogs,
and fish. They can be killed by proper cooking and freezing.
Molds and yeasts are examples of fungi, another concern of restaurant and
foodservice establishments. Fungi are mostly responsible for the spoilage of
many kinds of food, while some molds can produce harmful toxins. food
with molds that arc not a natural P~lft of the product should always be
discarded. Yeasts arc known tor their ability to spoil food rapidly. food
spoiled hv yeast should be discarded too.
Foodborne diseases are classified as infections, intoxications, or
toxin-mediated infections. Each occurs in a different \V~l~'. Foodborne
infections result when a person eats food containing pathogens, which
then grow in the intestines and cause illness. Typically, symptoms do not
appear immediately. Foodborne intoxications result when a person eats
food containing toxins produced by pathogens found on the food or which
are the result of a chemical contamination. The toxin might also come
from a plant or animal that was eaten. Typically, symptoms of toodborne
intoxication appear quickly, within a few hours. Foodbornc toxin-mediated
infections result when a person eats food that contain pathogens, which then
produce illness-causing toxins in the intestines.