Transcript Bacteria (Intermediate Level) - i

Intermediate Food Safety
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Aims
To explain the causes and effects of food poisoning
and its relevance to food safety
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Objectives
By the end of the lesson you should be able to:
1. Describe the different types of food poisoning
2. Understand how bacteria cause food poisoning
3. Identify different pathogenic bacteria and their
related symptoms
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What is Food Hygiene?
 The science of preserving health
 It involves all measures necessary to ensure the
safety and wholesomeness of food during it’s
preparation and storage
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What does it involve?
 Rejecting contaminated food
 Decontaminating food
 Protecting food from contamination through high
standards of personal hygiene, cleaning and
disinfection
 Preventing any organisms multiplying
 Destroying any harmful bacteria by thorough
cooking
 Discarding unfit or contaminated food
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Food Poisoning
 Normally associated with symptoms such as
diarrhoea and vomiting
 May also include headache, stomach cramps and
fever
 Bacteria are responsible for most cases
 Other causes include mycotoxins (poisonous
chemicals produced by some moulds)
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Food Poisoning (contd.)
 Physical
contamination:- objects
falling in to food – metal,
glass, packaging
materials etc.
 Chemical
contamination:- Bleach,
cleaning chemicals getting
in to food
 Natural
contamination:
Poisonous plants and
berries, undercooked red
kidney beans
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Poisonous mushrooms
The deathcap – one bite can prove fatal
And also…..The deadly Puffer fish!
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Most food poisoning is caused by?
Bacteria
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Vulnerable Groups
Food poisoning is more likely to affect people
with lowered resistance to disease than healthy
people who might show mild symptoms or none
at all.
The following are particularly vulnerable to food
poisoning: • Elderly or sick people
• Babies
• Young children
• Pregnant women
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Types of bacteria
 Spoilage: Not particularly
harmful bacteria which cause
food to go off
 Beneficial: “Good Bacteria”
which are used to make
yoghurt and cheese
 Pathogenic: Illness causing
bacteria
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In order to grow and multiply germs need:
Time
Moisture
Food
Warmth
Flies
Waiting
Remember it like this
Too
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Many
In ideal conditions where there is
Moisture, Food and Warmth
(37degrees centigrade is ideal),
bacteria can double every 10 to 20
minutes. They do this by dividing
in to two. This is called
Binary Fission
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These cells are beginning to divide into two
After 10 minutes
After 20 minutes
After 30 minutes
After 40 minutes
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cooking chicken to a core temperature
of 75°C should kill most of the bacteria
Time : 9.30
Bacteria : 0
Time : 9.40
Bacteria : 12,000
Time : 9.50
Bacteria : 24,000
Time : 10.00 Bacteria : 48,000
Time : 10.10
Bacteria : 96,000
Time : 10.20 Bacteria : 192,000
Time : 10.30 Bacteria : 384,000
Time : 10.40 Bacteria : 768,000
Time : 10.50 Bacteria : 1.5 million
From 0 to 1,536,000 in
only 80 minutes !!!!!!
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Knife
contaminated
by blood
Bacterial Growth Curve
Numbers
Of
Bacteria
rapid
multiplication
no multiplication
Lag Phase
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Stationary Phase
Numbers of
bacteria remain
constant as the
number
produced is
equal to the
number dying
Time (hours)
Numbers of
bacteria
decrease
Spore
A resting resistant phase of some bacteria
(including Clostridium Perfingens and
Botulinum and Bacillus Cereus). The
bacterium produces a protective coat
which helps it to survive high temperatures
(up to 120°C) and lack of water. When
favourable conditions return, the spores
split open and release the bacteria which
are then able to grow and multiply
Bacterial cell
Spore forming inside cell
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Spore Formation
This is what happens …………..
Cell
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Spore forms
in cell
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Cell
disintegrates
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Spore is
released
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Spore starts
to germinate
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Spore
continues to
germinate
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Now see as, in suitable conditions, the cell
begins to divide (binary fission)………………………….
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Toxins
Some bacteria release poisons known as
toxins which cause food poisoning. Some
toxins, known as exotoxins multiply in
food. These toxins are not easily
destroyed by cooking and may remain in
food once they have developed. Other
bacteria produce toxins inside the
human body only after the food has
been eaten. These are called endotoxins
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Moulds and Yeasts
 Moulds are a type of fungi that will grow on most
foods and at many temperatures. Some are used in
food production such as cheese manufacture.
Unwanted moulds usually spoil the food but do not
cause food poisoning.
 Yeasts are another type of fungi that will grow in
food. They are used in making food such as bread
and beer but also spoil many foods including jam,
fruit juice, yoghurts and meats
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Food Poisoning bacteria
•USUALLY NEED MILLIONS OF
BACTERIA TO CAUSE ILLNESS.
•THE MULTIPLICATION OF
BACTERIA WITHIN THE FOOD
PLAYS AN IMPORTANT PART IN
THE DISEASE
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Salmonella
Found in animals,
raw poultry and
birds
Bacillus Cereus
Found in soil,
vegetation,
cereals and
spices
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Staphylococcus
Aureus
Found in human
nose and throat
(also skin)
Clostridium
Perfingens
Found in animals
and birds
Clostridium
Botulinum
Found in the soil
and associated
with vegetables
and meats
Salmonella
 Sources - The intestines of ill people and
carriers, animals and animal food, raw
meat, raw poultry, raw milk, raw eggs, food
pests
 Common food vehicles – Undercooked
or contaminated cooked meat, raw milk and
eggs
 Onset period – 6 to 72 hours (usually 12
to 36) Endotoxin in intestine (infective food
poisoning)
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Salmonella
 Symptoms - Abdominal pain, diarrhoea,
vomiting and fever. Duration is usually one to
seven days.
 Specific characteristics – Usually requires
millions of bacteria to cause illness. Multiplies
from 5°C to 47°C under aerobic or anaerobic
conditions.
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Aerobic and Anaerobic
 Bacteria which need oxygen to multiply are classed
as aerobic
 Bacteria which only multiply without oxygen are
called anaerobic
 Just to confuse you some bacteria including
Salmonella, Staphylococcus aureus and Bacillus
cereus are classed as facultative anaerobes
which means they can multiply with or without
oxygen!
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Salmonella
Specific controls
 Hygienic farm and abbatoir practices
 Avoid cross contamination
 Complete thawing of frozen poultry
 Thorough cooking to 75°C for one minute
 High standards of personal hygiene
 Effective cleaning
 Safe sewage disposal
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Clostridium perfingens
 Sources - The intestines of humans and
animals, faeces and sewage, soil food pests, raw
meat and poultry
 Common food vehicles – Rolled joints,
casseroles, stews, sauces and meat pies when
cooking has removed oxygen
 Onset period – 8 to 22 hours (usually 12 to
18) Enterotoxin in intestine. (infective food
poisoning)
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Clostridium perfingens
 Symptoms - Abdominal pain, diarrhoea,
(vomiting is rare) and fever. Duration is usually 12
to 48 hours.
 Specific characteristics – Usually requires
millions of bacteria to cause illness. Multiplies
from 10°C to 52°C under anaerobic conditions. At
46°C it can double every 10 minutes. Produces
spores. Illness caused from consuming millions of
organisms
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Staphylococcus Aureus
 Sources - Human nose, mouth, skin, hands,
spots, boils, septic cuts etc
 Common food vehicles – Dairy products.
Cold cooked meat and poultry, peeled cooked
prawns
 Onset period – 1 to 7 hours (usually 12 to 18)
Exotoxin produced in food. (Toxic food
poisoning)
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Staphylococcus Aureus
 Symptoms - Abdominal pain, diarrhoea,
vomiting. Occasionally subnormal temperatures.
Duration between 6 and 24 hours.
 Specific characteristics – Usually requires
millions of bacteria to cause illness. Toxin may
survive boiling for up to 30 minutes. Multiplies
from 7°C to 48°C under aerobic or anaerobic
conditions. Can tolerate relatively high salt
content.
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Bacillus Cereus
 Sources - Cereals, especially rice, cornflour,
spices, dust and soil
 Common food vehicles – Reheated rice,
cornflour and spices.
 Onset period – 1 to 5 hours. Exotoxin
produced in food. (Toxic food poisoning)
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Bacillus Cereus
 Symptoms - Abdominal pain, diarrhoea,
vomiting. Occasionally subnormal temperatures.
Duration between 12 and 24 hours.
 Specific characteristics – Forms spores which
produce an exotoxin under aerobic or anaerobic
conditions. Both the spores and toxin will survive
normal cooking temperatures. Millions required
to cause illness. Bacteria multiply between 7°C and
48°C.
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Clostridium Botulinum
 Sources - Fish intestine, soil and vegetables.
 Common food vehicles – Low acid
processed food contaminated after canning or
vacuum packing. Smoked fish, bottled
vegetables.
 Onset period –2 hours to 5 days (usually 12
to 36 hours). A heat sensitive neurotoxin
produced in the food which affects the nervous
system. (Toxic food poisoning)
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Clostridium Botulinum
 Symptoms - Difficulties in swallowing, talking
and breathing. Double vision and paralysis.
Diarrhoea followed by constipation. Fatalities are
common and survivors may take several months to
recover.
 Specific characteristics – Forms spores which
produce an exotoxin under anaerobic conditions.
Both the spores and toxin will survive normal
cooking temperatures. Millions required to cause
illness. Bacteria multiply between 3.3°C and 48°C.
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Pathogenic Bacteria
Salmonella
Source
Raw meat
Poultry and eggs
Pests and pets
Human and animal intestines
Dirt and refuse
Symptoms
Vomiting
Nausea
Diarrhoea
Abdominal pain
Average Onset Time
12 - 36 hours
after eating
Staphylococcus
aureus
Human nose, throat, ears,
skin
Septic wounds
Animals and raw milk
Vomiting
Abdominal pain
Low temperature
1 – 7 hours after
eating
Clostridium
perfingens
Raw meat and poultry
Soil, dirt and refuse
Raw vegetables
Pests and pets
Human and animal intestines
Diarrhoea
Abdominal pain
12 - 18 hours
after eating
Clostridium
botulinum
Bacillus cereus
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Soil
Marine sediment
Raw fish and meat
Animal intestines
Dust and soil
Cereal, rice and pasta
Paralysis
Breathing and
swallowing difficulty
Diarrhoea followed by
constipation
Nausea
Vomiting
Abdominal pain
Diarrhoea
12 – 36 hours
after eating
1 - 5 hours or 8 –
16 hours
depending on the
form of the food
poisoning