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Microbiology
Microbiology is the study of micro-organisms
Micro-organisms are tiny living organisms that are not
visible to the eye
Classification of microorganisms
 Fungi:
moulds, yeast and large fungi
 Bacteria:
 Viruses:
like salmonella and E.coli
such as those which cause flu
and mumps
Terminology
•
Parasites: micro-organisms that feed on living matter
(humans/animals)
•
Saprophytes: micro-organisms that feed on dead organic matter
(food/soil)
•
Psychrophiles: thrive at low temp. -5oC to 20oC
•
Mesophiles: micro-organisms that thrive at temperatures between
20oC-45oC
•
Thermophiles: micro-organisms that thrive at higher temp. 45oC75oC
•
Aerobic: micro-organisms that need oxygen
•
Pathogens: bacteria that cause diseases
How microbes feed on food
•
All micro-organisms secrete enzymes onto
their food source.
•
These enzymes break down the food into
simple compounds.
•
These simple compounds are absorbed through
the cell wall and provide nourishment for
growth.
Fungi
•
Fungi do not make their own
food
•
Parasitic fungi feed on living
matter, e.g. athlete’s foot
•
Saprophytic fungi feed on
dead matter, e.g. Mushrooms
on soil
Classification of fungi
 Moulds
 Large
 Yeast
fungi (mushrooms)
Conditions required for growth of
moulds
•
Food: most moulds are saprophytes, feed from dead organic matter
e.g. Bread and cheese
•
Warmth: most are mesophiles. Freezing (-18oC) inactivates mould
growth.
•
Moisture: is needed for growth, thus frozen foods are unsuitable.
•
Oxygen: moulds are aerobic, need oxygen, so they will grow on the
surface of food e.g. jam or through open structure foods e.g. bread
•
pH level: moulds like slightly acidic conditions, extreme inhibit
growth
•
Time: moulds need time to multiply
Rhizopus
Structure of moulds
•
Moulds are multicellular fungi that can be seen on
food
•
Each mould begins as a spore on food
•
In favourable conditions, the spore develops a thin
thread-like filament called a hypha, which grows
down into the food
•
The hypha grows and branches out into hyphae,
which become intertwined becoming a mycelium
Structure contd..
Reproduction of moulds
•
Moulds reproduce both
1.
Asexually and
2.
Sexually
Asexual reproduction
•
When the mycelium is well established reproduction occurs as follows:
1.
A hypha grows upwards
2.
The head of the hypha can either be a sporangium (round) or a
conidium (chains of spores)
When ripe, the sporangium or conidium bursts, releasing spores
3.
which travel into the air
If the spore then finds suitable conditions, new mould growth
4.
begins.
•
* Copy
diagram from your textbook showing asexual reproduction
Sexual reproduction
•
Two hyphae grow beside each other
•
The two hyphae fuse together
•
The dividing wall breaks down and a zygospore develops.
•
The zygospore produces and stores spores
•
The zygospore has a thick wall and protects the spores until
there are suitable conditions
•
When conditions are suitable, the spores germinate, hyphae
grow and extend out
•
Spores are released into air and cycle begins again
Sexual reproduction
Classification of moulds
1.


Phycomycetes:
reproduce sexually or asexually
Produce sporangium from hyphae
Most favourable temperature at 30oC

Examples
Description
Grows on
Mucor
•Saprophytic mould
•Reproduces sexually and
asexually
•White hyphae
Bread
Soil
Rhizopus
•Saprophytic mould
•Reproduces asexually
•Fluffy white mycelium
Bread
Vegetables
Classification of moulds
2.



Examples
Ascomycetes
Reproduce asexually only
Conidium develop from the hyphae
Most favourable temperature between
oC
Description
Grows on
20oC-25
Penicillium
•Saprophytic mould
Cheese
•Green-blue mould
Bread
•Used in production of blueveined cheese and of antibiotics
Aspergillis
•Saprophytic mould
•Black mould
Fruit
Vegetables
Preventing food spoilage by
moulds
•
Store perishable items in fridge
•
Use food within the recommended
time
•
Cook food at high temperatures to
destroy moulds
•
Ensure that storage presses are
clean and dry
Large Fungi (mushrooms)
•
Large fungi are generally edible
•
They are visible to the naked
eye
•
They include many varieties:
1.
Field mushrooms e.g. Button
2.
Truffles-a delicacy are grown
underground
Reproduction of large fungi

Mushrooms start as spores

They produce hyphae which develop into mycelium on
suitable soil

The hyphae grow upwards

A tightly closed cap forms at the top of hyphae

This increase in size and opens as mushroom grows

Pink gills form underneath cap and spores are produced
here

When the mushrooms are ripe spores are released

If spores find suitable conditions, cycle begins again
Yeast - Saccharomycetes
•
Yeast is unicellular
•
Yeast is saprophytic (feed on dead
organic matter)
•
Yeast can spoil fruit, jam, mine and
meat
•
Some foodstuffs such as bread, beer
and vinegar rely on yeast for their
production.
Conditions for growth of yeast
•
Food: yeast feeds on carbohydrate foods
•
Warmth: optimum temp. 25oC-30oC. Yeast is killed at
temps above 60oC.
•
Moisture: yeast needs moisture
•
Oxygen: yeast is a facultative organism-so it can live
with or without oxygen
•
pH level: an acid environment is ideal for growth
•
Time: yeast needs time to grow
Structure of yeast
 Yeast
cells are oval shaped
 They have a thin outer wall enclosing
a granular cytoplasm
 Each
cell has a nucleus and vacuoles
which store food reserves
Structure of yeast
Yeast reproduction (budding)
•
Yeast cells reproduce asexually by
budding
1.
Under favourable conditions a yeast
cell develops a bud (bulge)
2.
The nucleus of the yeast cell moves
towards the bud
3.
The nucleus divides in two
4.
A wall develops, dividing the bud
from parent cell
5.
The bud separates from parent cell
Fungi
Advantages/benefits
Disadvantages/harmful effects
•Some are edible e.g.
•Fungi cause spoilage of food
Mushrooms
•Some fungi e.g. Amanita are
•Moulds are used in cheese
poisonous
production
•Fungi cause plant diseases,
•Moulds are used in production
e.g. Potato blight
of antibiotics e.g. Penicillin
•Some human diseases, e.g.
•Yeast is used in bread-making
Athlete’s foot, are caused by
and in brewing
fungi
Bacteria
•
Bacteria are microscopic
unicellular organisms.
•
They can be found
everywhere
•
Many are non-pathogenic
but some are pathogenic
Bacteria on an apple
Structure of a bacterial cell
Structure of a bacterial cell
•
Bacteria have:
•
A capsule for protection
•
•
A rigid cell wall for shape and structure
A cell membrane inside the cell wall to enclose a
colourless liquid called cytoplasm
•
Cytoplasm which contains nuclear membrane/DNA and
ribosomes
•
Flagella to help movement
Reproduction of bacteria
•
Bacteria reproduce asexually by a process called
binary fission- their offspring are genetically identical
•
Bacteria has a very short lifecycle (some can
reproduce every 20 minutes).
•
New mutations can spread very quickly
•
Rapid growth stops as bacteria compete for food,
oxygen, moisture and space.
In suitable conditions,
a mature bacterial cell
duplicates its nuclear
material and the
remaining cell divides
forming two cells.
Spore-forming bacteria
•
If conditions become unfavourable for bacterial growth, i.e. too
hot most bacteria die, but some are able to form spores.
•
The spores that develop within a bacterial cell are called
endospores.
•
The endospore grows and a tough wall develops around it.
•
The parent cell disintegrates releasing the spore which can stay
dormant for years until favourable conditions come again so
they can grow into new bacterial cells
The formation of spores
Spore-forming bacteria
•
Bacilli and clostridia
bacteria (food poisoning)
have the ability to form
spores, which are highly
resistant to heat, cold,
and disinfectants
Clostridium difficile bacteria is a
common hospital acquired
infection
Toxins
 During
rapid growth some bacteria produce
waste called toxins.
 Toxins or poisons are often a cause of
food poisoning and may be produced in two
different ways: exotoxins and endotoxins
Exotoxins

Exotoxins are produced outside the bacterial cells as they grow in
food.

They are produced both before and after the food is eaten and are
responsible for toxic food poisoning.

Clostridium botulinum is an example of a bacteria that produce
exotoxins

While commercially canned goods are required to undergo a "botulinum
cook" at 121 °C (250 °F) for 3 minutes, and so rarely cause botulism,
there have been notable exceptions such as the 1978 Alaskan salmon
outbreak. Foodborne botulism has more frequently been from homecanned foods with low acid content, such as green beans and corn.
•
Endotoxins
Endotoxins are produced within the bacterial cells as they
grow.
•
They are released when the bacteria die.
•
Salmonella and listeria bacteria produce endotoxins and
are responsible for infectious food poisoning
•
Most people who get infected with Salmonella develop
diarrhoea, fever, vomiting, and abdominal cramps, 12 to 72
hours after infection. In most cases, the illness lasts 3 to
7 days.
Classification of bacteria
•
Bacteria are
classified by:
a)
Shape
b)
Gram Staining
Shape - Spherical (cocci)
In clusters-staphylococci
Food poisoning
In chains - streptococci
Sore throat
Shape - Rod (bacillus)
 Food
poisoning – salmonella, listeria, E.coli,
clostridium botulinum
Shape – Spiral (spirilla)
 Sexually
transmitted diseases, e.g. Syphilis
Gram staining
•
Bacteria may be classified as:
a)
Gram-positive
b)
Gram negative
•
Blue/purple
Depending on the results of the gram-stain
Pink
test
Gram staining

Inoculate an agar plate with bacteria and incubate (allow
grow)

Pour crystal violet dye over the cells (blue colour)

Pour an iodine solution over the cells (blue-black colour)

Pour a solvent e.g. Alcohol over the cells and note the
results

Gram positive = blue/purple colour

Gram negative = pink colour
Gram staining procedure
Characteristics of bacteria
Gram-positive bacteria
Gram-negative bacteria
•Cell wall is one thick layer
•Cell wall is two thin layers
•No flagellae
•Flagellae present
•Spore forming
•Non-spore forming
•Low resistance to antibiotics •High resistance to antibiotics
•E.g. Streptococci and
clostridia
•E.g. Salmonella, E.coli
Conditions for growth of bacteria

Food: saprophytic bacteria are on food and cause its
decomposition. Parasitic bacteria cause disease in humans

Warmth: bacteria have a wide temp range. Most are
mesophiles

Moisture: is needed in liquid form, e.g. Meat

Oxygen: most are aerobic, e.g. E.coli. Some are anaerobic,
e.g. Clostridium botulinium

pH level: thrive best in neutral conditions

Time: bacteria will double every 20mins in ideal conditions
Past exam Questions – do one or more of
these as additional optional Homework.
 2004
Higher level – Section B – Qs.2
 2008 Higher level – Section B – Qs. 3