Presentation on theme: "Microbiology Microbiology is the study of micro- organisms"— Presentation transcript:
1Microbiology Microbiology is the study of micro- organisms Micro-organisms are tiny living organisms that are not visible to the eye(c) PDST Home Economics
2Classification of micro-organisms Fungi: moulds, yeast and large fungiBacteria: like salmonella and E.coliViruses: such as those which cause flu and mumps
3TerminologyParasites: 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 20oCMesophiles: micro-organisms that thrive at temperatures between 20oC-45oCThermophiles: micro-organisms that thrive at higher temp. 45oC- 75oCAerobic: micro-organisms that need oxygenPathogens: bacteria that cause diseases
4How 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.
5Fungi Fungi do not make their own food Parasitic fungi feed on living matter, e.g. athlete’s footSaprophytic fungi feed on dead matter, e.g. Mushrooms on soil
6Classification of fungi MouldsLarge fungi (mushrooms)Yeast
7Conditions for growth of moulds Food: most moulds are saprophytes, feed from dead organic matter e.g. Bread and cheeseWarmth: 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. breadpH level: moulds like slightly acidic conditions, extreme inhibit growthTime: moulds need time to multiply
9Structure of mouldsMoulds are multicellular fungi that can be seen on foodEach mould begins as a spore on foodIn favourable conditions, the spore develops a thin thread-like filament called a hypha, which grows down into the foodThe hypha grows and branches out into hyphae, which become intertwined becoming a mycelium
11Reproduction of moulds Moulds reproduce bothAsexually andSexually
12Asexual reproductionWhen the mycelium is well established reproduction occurs as follows:A hypha grows upwardsThe 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 airIf the spore then finds suitable conditions, new mould growth begins.
13Sexual reproduction Two hyphae grow beside each other The two hyphae fuse togetherThe dividing wall breaks down and a zygospore develops.The zygospore produces and stores sporesThe zygospore has a thick wall and protects the spores until there are suitable conditionsWhen conditions are suitable, the spores germinate, hyphae grow and extend outSpores are released into air and cycle begins again
15Classification of moulds Phycomycetes:reproduce sexually or asexuallyProduce sporangium from hyphaeMost favourable temperature at 30oCExamplesDescriptionGrows onMucorSaprophytic mouldReproduces sexually and asexuallyWhite hyphaeBreadSoilRhizopusReproduces asexuallyFluffy white myceliumVegetables
16Classification of moulds AscomycetesReproduce asexually onlyConidium develop from the hyphaeMost favourable temperature between 20oC-25oCExamplesDescriptionGrows onPenicilliumSaprophytic mouldGreen-blue mouldUsed in production of blue-veined cheese and of antibioticsCheeseBreadAspergillisBlack mouldFruitVegetables
17Preventing food spoilage by moulds Store perishable items in fridgeUse food within the recommended timeCook food at high temperatures to destroy mouldsEnsure that storage presses are clean and dry
18Large Fungi (mushrooms) Large fungi are generally edibleThey are visible to the naked eyeThey include many varieties:Field mushrooms e.g. ButtonTruffles-a delicacy are grown underground
19Reproduction of large fungi Mushrooms start as sporesThey produce hyphae which develop into mycelium on suitable soilThe hyphae grow upwardsA tightly closed cap forms at the top of hyphaeThis increase in size and opens as mushroom growsPink gills form underneath cap and spores are produced hereWhen the mushrooms are ripe spores are releasedIf spores find suitable conditions, cycle begins again
20Yeast - Saccharomycetes Yeast is unicellularYeast is saprophytic (feed on dead organic matter)Yeast can spoil fruit, jam, mine and meatSome foodstuffs such as bread, beer and vinegar rely on yeast for their production.
21Conditions for growth of yeast Food: yeast feeds on carbohydrate foodsWarmth: optimum temp. 25oC-30oC. Yeast is killed at temps above 60oC.Moisture: yeast needs moistureOxygen: yeast is a facultative organism-so it can live with or without oxygenpH level: an acid environment is ideal for growthTime: yeast needs time to grow
22Structure of yeast Yeast cells are oval shaped They have a thin outer wall enclosing a granular cytoplasmEach cell has a nucleus and vacuoles which store food reserves
24Yeast reproduction (budding) Yeast cells reproduce asexually by buddingUnder favourable conditions a yeast cell develops a bud (bulge)The nucleus of the yeast cell moves towards the budThe nucleus divides in twoA wall develops, dividing the bud from parent cellThe bud separates from parent cell
25Fungi Some are edible e.g. Mushrooms Advantages/benefitsDisadvantages/harmful effectsSome are edible e.g. MushroomsMoulds are used in cheese productionMoulds are used in production of antibiotics e.g. PenicillinYeast is used in bread-making and in brewingFungi cause spoilage of foodSome fungi e.g. Amanita are poisonousFungi cause plant diseases, e.g. Potato blightSome human diseases, e.g. Athlete’s foot, are caused by fungi
26Bacteria Bacteria are microscopic unicellular organisms. They can be found everywhereMany are non- pathogenic but some are pathogenicBacteria on an apple
28Structure of a bacterial cell Bacteria have:A capsule for protectionA rigid cell wall for shape and structureA cell membrane inside the cell wall to enclose a colourless liquid called cytoplasmCytoplasm which contains nuclear membrane/DNA and ribosomesFlagella to help movement
29Reproduction of bacteria Bacteria reproduce asexually by a process called binary fission- their offspring are genetically identicalBacteria has a very short lifecycle (some can reproduce every 20 minutes).New mutations can spread very quicklyRapid growth stops as bacteria compete for food, oxygen, moisture and space.
30In suitable conditions, a mature bacterial cell duplicates its nuclear material and the remaining cell divides forming two cells.
31Spore-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
33Spore-forming bacteria Bacilli and clostridia bacteria (food poisoning) have the ability to form spores, which are highly resistant to heat, cold, and disinfectantsClostridium difficile bacteria is a common hospital acquired infection
34Toxins 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
35ExotoxinsExotoxins 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 exotoxinsWhile 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.
36EndotoxinsEndotoxins 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 poisoningMost 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.
37Classification of bacteria Bacteria are classified by:ShapeGram Staining
40Shape – Spiral (spirilla) Sexually transmitted diseases, e.g. Syphilis
41Gram staining Bacteria may be classified as: Gram-positive Gram negativeDepending on the results of the gram-stain testBlue/purplePink
42Gram stainingInoculate 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 resultsGram positive = blue/purple colourGram negative = pink colour
44Characteristics of bacteria Gram-positive bacteriaGram-negative bacteriaCell wall is one thick layerCell wall is two thin layersNo flagellaeFlagellae presentSpore formingNon-spore formingLow resistance to antibioticsHigh resistance to antibioticsE.g. Streptococci and clostridiaE.g. Salmonella, E.coli
45Conditions for growth of bacteria Food: saprophytic bacteria are on food and cause its decomposition. Parasitic bacteria cause disease in humansWarmth: bacteria have a wide temp range. Most are mesophilesMoisture: is needed in liquid form, e.g. MeatOxygen: most are aerobic, e.g. E.coli. Some are anaerobic, e.g. Clostridium botuliniumpH level: thrive best in neutral conditionsTime: bacteria will double every 20mins in ideal conditions
46Past exam Questions 2004 Higher level – Section B – Qs.2 2005 Ordinary level – Section B – Qs.3Throughout short questions.