Microbiology

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 hyphagrows upwards • The head of the hypha can either be a sporangium (round) or a conidium (chains of spores) • When ripe, the sporangium or conidiumbursts, 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 zygosporeproduces 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

16. Classification of moulds • Ascomycetes • Reproduce asexually only • Conidium develop from the hyphae • Most favourable temperature between 20oC-25oC

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 isunicellular • 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

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

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.