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41 Cards in this Set
- Front
- Back
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Typical length of bacteria |
1 - 3 ųm |
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Bacillus |
Rod-shaped |
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Coccus |
Spherical |
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Spirillum |
Spiral-shaped |
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What causes the shapes of bacteria? |
Their rigid cell wall's unique structure |
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What is found in the cell wall? |
Peptidoglycan / murein |
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How does peptidoglycan enforce the cell wall? |
Cross-linking provides strong and flexible framework and prevents the cell from lysis |
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What is peptidoglycan made from? |
A mixture of hexose sugars and amino acids |
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Characteristics of Gram- positive bacteria |
Thicker cell wall No lipopolysaccharide layer Are stained purple by crystal violet/iodine complex |
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Characteristics of Gram-negative bacteria |
Thinner cell wall Have a lipopolysaccharide layer Are stained red by counterstain saffranin |
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What protection does the lipopolysaccharide layer provide? |
Protection from lysozyme Resistance to penicillin |
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Process of Gram-staining |
Heat the slide to fix bacteria Flood the slide with crystal violet dye Rinse with water Flood the slide with iodine (binds with dye) Rinse with water Decolourize with ethanol (+ve stay purple) Rinse with water Flood the slide with saffranin (-ve turn red) |
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Autotrophic |
Carbon obtained from CO2 |
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Heterotrophic |
Carbon obtained from organic compounds |
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Chemotrophic |
Energy obtained from external chemical compounds |
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Phototrophic |
Energy obtained from light |
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Obligate aerobes |
Require oxygen for metabolism |
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Faculative anaerobes |
Can respire anaerobically if there is little or no oxygen available |
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Obligate anaerobes |
Can only survive in the absence of oxygen (oxygen is toxic to them) |
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Antigens |
Unique proteins found on the surface of bacteria |
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How can bacteria be classified from their antigenic features? |
By carbohydrate or protein antigens Found on the cell wall or the capsular polysaccharide |
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Vertical transmission |
Transfer of DNA via asexual reproduction of bacteria |
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Horizontal transmission |
Transfer of DNA in plasmids via pili |
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What nutrients are needed for bacterial growth |
Carbon compounds (organic) (eg. Glucose for energy) Nitrogen compounds (organic or inorganic) to produce amino acids for proteinsynthesis Mineral salts and vitamins |
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What is the optimum temperature for bacterial growth? |
25 - 45 °C |
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Optimum temperature for mammalian pathogens |
37°C (don't grow at this temperature when cultivating bacteria that don't require this temperature) |
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Other requirements for bacteria growth |
Oxygen - does depend on if an aerobe or anaerobe but does prevent growth of harmful pathogens if present Water |
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Optimum pH for bacterial growth |
Slightly alkaline (pH 7.4) |
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Why would the pH of the medium change during bacterial growth? |
Production of acidic/alkaline products by bacteria |
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How to prevent change of pH of medium? |
Use of an appropriate sterile buffer solution |
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Bacterial growth curve |
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Aseptic technique function |
Prevents the contamination of the environment by the microbes and the contamination of the culture by unwanted microbes |
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Sterilisation |
The removal/killing of microorganisms on an object or in any material |
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Methods of sterilisation |
Heat the equipment in an autoclave at 121°C for 15 minutes Heat the inoculating loop in a Bunsen Burner flame Irradiation of heat labile plastics |
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Aseptic technique methods |
Wash work bench with disinfectant Wash hands with antibacterial soap Flame bottle neck of culture solution Flame inoculating loop Have a Bunsen Burner near work area Never open Petri dish fully Don't place bottle lid on workbench |
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Where we should measure bacterial growth |
In food premises inspected by environmental food officers Water boards check water supplies In the production of food products in fermenters |
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Viable count |
A count of the living cells only |
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Viable count method |
Spread a known volume of organisms from each serial dilution onto an what plate and allow it to incubate at 25°C |
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Viable count formula |
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Total cell count |
Count of both living and dead cells |
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Total cell count method |
Use turbidimetry (measure of cloudless of solution by using a colorimeter) Turbidity increases = Cell numbers increase |
