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. -5oC to 20oC
Mesophiles: micro-organisms that thrive at temperatures between 20oC-45oC
Thermophiles: micro-organisms that thrive at higher temp. 45oC- 75oC
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
Asexually and
Sexually

12. Asexual reproduction
When the mycelium is well established reproduction occurs as follows:
A hypha grows upwards
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 which travel into the air
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
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
Reproduces asexually
Fluffy white mycelium
Vegetables

16. Classification of moulds
Ascomycetes
Reproduce asexually only
Conidium develop from the hyphae
Most favourable temperature between 20oC-25oC
Examples
Description
Grows on
Penicillium
Saprophytic mould
Green-blue mould
Used in production of blue-veined cheese and of antibiotics
Cheese
Bread
Aspergillis
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:
Field mushrooms e.g. Button
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. 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

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
Under favourable conditions a yeast cell develops a bud (bulge)
The nucleus of the yeast cell moves towards the bud
The nucleus divides in two
A wall develops, dividing the bud from parent cell
The bud separates from parent cell

25. Fungi Some are edible e.g. Mushrooms
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:
Shape
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: Gram-positive
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. 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

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
2005 Ordinary level – Section B – Qs.3
Throughout short questions.