Presentation on theme: "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."— Presentation transcript:
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
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
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. -5 o C to 20 o C Mesophiles: micro-organisms that thrive at temperatures between 20 o C-45 o C Thermophiles: micro-organisms that thrive at higher temp. 45 o C- 75 o C 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 fungi (mushrooms) Yeast
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
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
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) 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.
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
Classification of moulds 1.Phycomycetes: reproduce sexually or asexually Produce sporangium from hyphae Most favourable temperature at 30 o C ExamplesDescriptionGrows 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.Ascomycetes Reproduce asexually only Conidium develop from the hyphae Most favourable temperature between 20 o C-25 o C ExamplesDescriptionGrows 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
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. 25 o C-30 o C. Yeast is killed at temps above 60 o 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
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/benefitsDisadvantages/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
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
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 home- canned foods with low acid content, such as green beans and corn.home- cannedbeanscorn
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. diarrhoeafevervomitingabdominal cramps
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 – Spiral (spirilla) Sexually transmitted diseases, e.g. Syphilis
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
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
Gram-positive bacteriaGram-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
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 2004 Higher level – Section B – Qs Higher level – Section B – Qs Ordinary level – Section B – Qs.3 Throughout short questions.