not by me by pdst

1. Microbiology
Microbiology is the study of micro-
organisms
Micro-organisms are tiny living organisms
that are not visible to the eye
(c) PDST Home Economics

2. Classification of micro-organisms
• Fungi: moulds, yeast and large
fungi
• Bacteria: like salmonella and
E.coli
• Viruses: such as those which
cause flu and mumps

3. 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. -5o
C to 20o
C
• Mesophiles: micro-organisms that thrive at temperatures between
20o
C-45o
C
• Thermophiles: micro-organisms that thrive at higher temp. 45o
C-
75o
C
• Aerobic: micro-organisms that need oxygen
• Pathogens: bacteria that cause diseases

4. 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.

5. 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

6. Classification of fungi
• Moulds
• Large fungi (mushrooms)
• Yeast

7. Conditions 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: mould 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

8. Rhizopus

9. 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

10. Structure contd..

11. Reproduction of moulds
• Moulds reproduce both
1.Asexually and
2.Sexually

12. 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)
3. When ripe, the sporangium or conidium bursts, releasing
spores which travel into the air
4.If the spore then finds suitable conditions, new mould
growth begins.

13. 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

14. Sexual reproduction

15. Classification of moulds
1. Phycomycetes:
• reproduce sexually or asexually
• Produce sporangium from hyphae
• Most favourable temperature at 30o
C
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

16. Classification of moulds
2. Ascomycetes
• Reproduce asexually only
• Conidium develop from the hyphae
• Most favourable temperature between 20o
C-25o
C
Examples Description Grows on
Penicillium •Saprophytic mould
•Green-blue mould
•Used in production of blue-veined
cheese and of antibiotics
Cheese
Bread
Aspergillis •Saprophytic mould
•Black mould
Fruit
Vegetables

17. 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

18. 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

19. 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

20. 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.

21. Conditions for growth of yeast
• Food: yeast feeds on carbohydrate foods
• Warmth: optimum temp. 25o
C-30o
C. Yeast is killed at
temps above 60o
C.
• 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

22. 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

23. Structure of yeast

24. 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

25. Fungi
Advantages/benefits Disadvantages/harmful effects
•Some are edible e.g. Mushrooms
•Moulds are used in cheese
production
•Moulds are used in production of
antibiotics e.g. Penicillin
•Yeast is used in bread-making
and in brewing
•Fungi cause spoilage of food
•Some fungi e.g. Amanita are
poisonous
•Fungi cause plant diseases, e.g.
Potato blight
•Some human diseases, e.g.
Athlete’s foot, are caused by fungi

26. Bacteria
• Bacteria are
microscopic unicellular
organisms.
• They can be found
everywhere
• Many are non-
pathogenic but some
are pathogenic Bacteria on an apple

27. Structure of a bacterial cell

28. 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

29. 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.

30. In suitable conditions,
a mature bacterial cell
duplicates its nuclear
material and the
remaining cell divides
forming two cells.

31. 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

32. The formation of spores

33. 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

34. 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

35. 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 home-
canned foods with low acid content, such as green beans and corn.

36. 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.

37. Classification of bacteria
• Bacteria are
classified by:
a)Shape
b)Gram Staining

38. Shape - Spherical (cocci)
In clusters-staphylococci
Food poisoning
In chains - streptococci
Sore throat

39. Shape - Rod (bacillus)
• Food poisoning – salmonella, listeria, E.coli,
clostridium botulinum

40. Shape – Spiral (spirilla)
• Sexually transmitted diseases, e.g. Syphilis

41. Gram staining
• Bacteria may be classified as:
a)Gram-positive
b)Gram negative
• Depending on the results of the gram-stain
test
Blue/purple
Pink

42. 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

43. Gram staining procedure

44. 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
Characteristics of bacteria

45. 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

46. Past exam Questions
• 2004 Higher level – Section B – Qs.2
• 2008 Higher level – Section B – Qs. 3
• 2005 Ordinary level – Section B – Qs.3
• Throughout short questions.