Food Hygiene 2 - Bacteria and their characteristics Suitable for REHIS Elementary Food Hygiene Course

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Bacteria and their
characteristics
Food Hygiene 2

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Be able to explain
what is meant by the
term ‘danger zone’,
To know what is meant
by the term ‘‘high risk
food’
To know the difference
between the terms,
‘pathogen’ and ‘food
spoilage’
To show progress today I should …

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We are learning …
1.Where bacteria may be found
2.The general structure, shape and size of bacteria
3.How bacteria multiply, how quickly this may occur and the ideal conditions for multiplication
to take place
4.What is meant by a ‘high risk food’
5.What is meant by the term ‘danger zone’
6.The formation of bacterial spores and toxins, their function and methods by which they may
be destroyed.
7.The terms ‘pathogen’ and ‘food spoilage’
8.The difference between pathogenic and food spoilage bacteria
9.Food Preservation; how the multiplication of pathogens & spoilage organisms can by
inhibited by:
(a) Low temperatures, thorough cooking, hot holding and reheating, high temperatures,
dehydration, vinegar vacuum packing and the use of chemical preservatives
10.How bacteria can be destroyed

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Microbiological hazards (bacteria)
Microbiological hazards include the;
Contamination of food by bacteria, viruses and moulds.
Multiplication of bacteria within food
Survival of bacteria or other pathogens because of
inadequate cooking or processing.

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Bacteria
• Bacteria are very
small – millions
would fit on the
point of a pin

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1,000,000 bacteria can fit on the head of a pin

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Bacterium are so small
a microscope is needed to see them.
Bacteria are microscopic organisms,
often referred to as germs.

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Difference between
Food Spoilage and Pathogens
A small number of Spoilage Bacteria cause food to perish, spoil
or become unfit to eat.
Other bacteria, such as food poisoning bacteria are known as
Pathogens. If pathogens get into food, they make people ill.
Pathogens have no effect on the appearance, taste or smell of
food and can only be detected by laboratory testing.
Different types of bacteria vary in shape.

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Salmonella Enteritidis

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Food poisoning bacteria - Pathogens
It is not possible to operate a food business
without food poisoning bacteria being
present at one time or another.
It is therefore essential that we prevent
food poisoning by denying pathogens the
conditions which allow them to multiply to
a level where they present a risk to the
consumer.

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Bacterial Multiplication
Important that we know the things that bacteria need to multiply so we
can then manipulate them in order to prevent bacterial multiplication.
Bacteria responsible for causing food poisoning need these conditions to
enable them to multiply and produce toxins (poisons). Toxins may be
released in our bodies or in the food. Some toxins cannot be destroyed
by normal cooking and are very dangerous.
moisture warmth
food time

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Temperature Control
Most spore-bearing bacteria are destroyed
Most bacteria are destroyed
Bacteria multiplication prevented, some bacteria may survive
Danger Zone 5oC - 63oC
Bacteria multiply rapidly over this temperature range
Some bacteria multiply slowly 1oC - 4oC
Bacterial multiplication is stopped ≤-18oC - 0oC

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Warmth
To prevent the growth of food poisoning
bacteria ensure that the temperature of food
is kept
below 5oC or above 63oC.
The best temperature for the multiplication of most food
poisoning bacteria is around 37oC (body temperature).
Bacteria can multiply quickly between 20oC and 50oC.

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Warmth
The temperature range from
5oC to 63oC is known as the
‘danger zone’. It is where bacteria
grow and multiply.
Most will not grow in a refrigerator
(1oC to 4oC) and none will grow in
frozen food (-18oC).
Many will survive being frozen and
start multiplying when the food
thaws. Bacteria asleep
below freezing point
Growth
slows down
Bacteria
multiply
rapidly
Bacteria
start to die
Most bacteria
die at cooking
temperature

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Food and moisture
Bacteria prefer foods which contain nutrients
and moisture especially raw or cooked meat,
poultry and dairy produce
Food is categorised into the following groups:
High-risk foods - (usually protein rich and already cooked)
Low-risk foods
Raw foods to be cooked
Ready-to-eat raw foods
Foods such as dried egg or milk powder do not provide the
moisture necessary for the growth of bacteria.

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Time
Given the right conditions of food, moisture and warmth,
some bacteria can divide into two every ten minutes.
This process is known as binary fission.
If there is sufficient time, a few bacteria can multiply to such an extent that
there are enough present to cause food poisoning.
For this reason it is essential that high-risk foods are not left in the danger
zone for longer than is absolutely necessary.

18. nts will be able to explain how the food poisoning chain may be broken.
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Binary Fission
(Cell division)
Given the right conditions
of food, moisture and
warmth, some bacteria
can divide into two every
ten minutes.

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Microbiological multiplication
In 2 hours, 1 bacterium can divide and become 2,048 bacteria
1,000 bacteria can become millions of bacteria
in 1 hour and 40 minutes given the right conditions. . (1024000 )

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Cell Division
Binary Fission

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Bacterial Spores
Some bacteria can produce spores, which protect them
against harmful conditions such as high temperatures,
drying and disinfection.
Some spores can survive boiling for up to 5 hours.
It is important that we know the things that bacteria
need to multiply so we can then manipulate them
in order to prevent multiplication.

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Spores are a resting phase and they do not
multiply. The spores release the bacterium
when favourable conditions return.
This process is known as germination.

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Formation of bacterial spores
Some bacteria can
produce spores
when conditions
are unfavourable:
A dormant,
resistant state.

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Bacterial spores - Clostridium botulinum
(Botulism Botox is made from this bacteria)
The most dangerous spore-former is Clostridium botulinum
(Botulism Botox is made from this bacteria) which produces a
potent neurotoxin that can prove fatal.
Origin: Soil, Risky food: Faulty processed canned meat and
vegetables; cured meat and raw fish.
The most common food poisoning from a spore-former is
caused by C. perfringens.
Origin: The environment
Risky food: large joints of meat; reheated gravies
Other food poisoning spore-formers include Bacillus cereus (cooked rice), B. subtilis
and B. lichenifor

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Chilled Storage
Prevents most bacteria from multiplying
Slows down food spoilage
Fridge temperature 1⁰C to 4⁰C
Frozen Food
No bacterial growth
Spores and dormant bacteria will survive
Freezer temperature -18⁰C

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RECORD THE TEMPERATURE,
date and time taken
Thorough cooking will destroy most harmful bacteria
• The centre, or coldest part of the food, should achieve
75oC during cooking (or 70⁰C for 2 minutes)
• 82oC for reheating
• Only reheat once

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High Risk Foods
These are foods which are ready-to-eat and are cooked (or intended for
eating without cooking) which would destroy such bacteria
High Risk Foods support the multiplication of harmful bacteria.
• Cooked meat and cooked poultry
• Cooked meat products like gravy, stock, meat pies
• Dairy - milk, cream, artificial cream, soft cheese, custard
• Eggs and products made from raw eggs like mayonnaise
• Shellfish and other seafood like prawns, crab, oysters
• Cooked rice

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High Risk Foods
High risk foods usually contain proteins
• Protect them from contamination
• Keep them refrigerated to prevent bacteria multiplying
• Keep separate from raw food
Cooked pasta, bean sprouts, jacket potatoes, cut tomatoes and cut melons
have all been implicated in food poisoning outbreaks and should be
considered as high-risk foods.
High risk foods are often involved in outbreaks of food poisoning. Unfortunately, contaminated
foods usually look, taste and smell completely normal and are unlikely to be detected.
Raw meat for cooking is not considered to be high-risk food because food poisoning bacteria
will be destroyed by cooking.

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Low Risk Foods
Bacteria cannot multiply in dried food. Foods containing high
concentrations of sugar, salt, acid and other preservatives.
• Bread
• Dried Pasta
• Uncooked (dried) rice
• Dried pulses and grains
• Biscuits
• Jam
• Canned food
• Crisps
• Breakfast cereals like Cornflakes, Weetabix
When water is added to dried food such as milk powder it becomes high-risk and must be stored under refrigeration or
used immediately

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Raw foods to be cooked
Keep separate from ready to eat foods.
The food poisoning organisms
will be destroyed by thorough cooking.
Raw foods are likely to be already contaminated with large
numbers of food poisoning organisms and must be kept
separate from ready-to-eat foods

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Raw foods such as salads or fruit may be
contaminated with bacteria and viruses which only
need to be present in low numbers to cause illness.
Ensure ready-to eat raw foods are washed thoroughly
under running water before eating
Note
Beansprouts, cut melons, tomatoes, raspberries,
spinach and lettuce have been involved in food
poisoning outbreaks.
Ready-to-Eat Raw Foods

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Food Preservation
Preservation is the treatment of food to remove or
change the conditions required for bacteria to multiply
• High temperatures - The high temperatures (100oC ) kill bacteria.
(pasteurisation, UHT, sterilisation, cooking, canning & bottling)
• Low temperatures - The low temperatures bacteria do not grow.
(refrigeration & freezing)
• Dehydration - The bacteria do not grow without air.
• Chemicals - antimicrobial chemicals inhibits bacterial growth & antioxidants prevents oxidation.
• Vacuum packing - The bacteria do not grow without air.
• Pickling - Vinegar is alkaline, most bacteria grow best around neutral pH values (6.5 - 7.0)
• Irradiation - Energy from irradiation destroys most of the bacteria.
• Smoking - Smoke prevents oxidation and slows bacterial growth.

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Chemical Preservatives
Pickling – Using vinegar
e.g. Pickled onions
Smoking – Smoked Fish
Salting - Salt cured ham
Jam Making – Using large amounts of sugar to prevent
bacterial growth
Once opened, the food should be treated as fresh and stored under refrigeration.
Pasteurised, smoked & vacuumed packed meat/fish should also be stored chilled in the fridge

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The Food Chain
Food safety at all steps
From
Production
to
Processing
to
Distribution
to
Restaurant Kitchen or Shop
to
Food Preparation
to
Consumer

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Click Play ► to view
Example of food spoilage
Strawberry.
Food spoilage is food going off
This is NOT food poisoning.
Unlike food contaminated with
pathogens the effects of food
spoilage may change:
• appearance
• taste
• texture
• odour
Food become unsafe to eat.

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• Off odours
• Slime/stickiness
• Changes in texture
• Production of gas
• Discolouration
• Mould growth
• Unusual taste
• Blown cans or leaking packs
A small number bacteria known as Spoilage Bacteria, cause food to perish, spoil or become
unfit. Food Spoilage bacteria is different from food poisoning bacteria
We do not normally eat spoilt food because it smells ‘off’ and may be slimy and rotten
Food spoilage

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Food soilage and pathogens dormant.
No growth below freezing point
Food spoilage slow growth
Most pathogens no growth (<5oC)
Bacteria multiply (5oC - 63oC)
Rapidly multiply (20oC - 50oC)
Destroys most pathogens
Too Hot bacteria start to die at 63oC
Dead
Most bacteria die at cooking temperature
Danger
Zone
5oC - 63oC

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The best temperature for bacteria to grow is 37oC

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Danger Zone is between
5oC - 63oC
Cook food to at least 75oC

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Chill and Frozen Temperatures
Fridge temperature
1oC – 4oC
Raw meat and fish
at bottom of fridge
Freezer temperature
-18oC

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Reheating Food
Reheated foods should be heated to 82oC
Don’t reheat food more than once.
With chicken or meat, a temperature probe/thermometer should be
used before cooking, if the item has been frozen, to check it has
defrosted properly. It should also be used after cooking to ensure the
chicken or meat has been thoroughly cooked. The probe/thermometer
should be washed in between to prevent cross-contamination.

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Your responsibility
To learn about bacteria and how they can be controlled
To protect food from contamination
To make sure spoilt or unfit food is not sold

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What the law says
• Chilled food must be stored in a
refrigerator or in a cool ventilated place
• Hot food must be stored above 63⁰C
• Re-heated products must reach a
minimum of 82⁰C

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Be able to explain
what is meant by the
term ‘danger zone’,
To know what is meant
by the term ‘‘high risk
food’
To know the difference
between the terms,
‘pathogen’ and ‘food
spoilage’
How well did you do?

45. ©2022 The Joyful Class
Credits
Royalty-Free Images used with under licence Shutterstock,
Think emoji, brain, darts board, bacteria on pin, pin on finger, Bacteria under microscope, blue bacteriumm, salmonella, cell
division, spore formation, anatomy of a cell, germ chef, tap icon, chicken icon, thermometer icon, clock icon, colourful
thermometer, bacteria in water, chef germ holding a burger, chef recording temperature, pulses, raw meats, bean sprouts,
tomato, cut tomato, melon washing salad vegetables, preserves and canning cartoon, chutney, food chain from production
to distribution, video of food spoilage in strawberry, food spoilage of lemon, blank thermometer, fridge, recording
thermometer reading, reheat food temperature
Images used under licence of The Joyful Class
The Germometer, Core Temperature of meat and Bacteria multiplication