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Flashcards

MICROSCOPY & CELL MORPHOLOGY

Simmy Braich English 33 cards

Cards in this deck (33)

  1. 1THE LIGHT MICROSCOPE - BRIGHT FIELD-relies on the contrast b/w bacteria and the medium
    - usually requires stains to increases contrast
    - highest resolution 0.2micro mm
  2. 2THE LIGHT MICROSCOPE - DARK FIELD- light reaches slide from side only
    - bacteria appears light against dark background
    - high resolution
  3. 3THE LIGHT MICROSCOPE - PHASE CONTRAST- doesn't require stains for contrast
    - can look at live cells/wet mounts.
  4. 4THE LIGHT MICROSCOPE - FLUORESCENCE- used to visualise cells that fluoresce naturally or that have been fluorescently labelled.
    - commonly used in diagnostic microbiology
  5. 5THE ELECTRON MICROSCOPE- used for studying detailed structure of cells
    - electrons rather than light waves
    1. Transmission electron microscopy
    2. scanning electron microscopy
  6. 6TRANSMISSION ELECTRON MICROSCOPY- uses very thin sections stained with special electron dense stain
  7. 7SCANNING ELECTRON MICROSCOPY- can use whole cell to show external features
  8. 8STAINING BACTERIA- increase contrast for viewing
    - provide information regarding cell type/shape/size
    -cell wall
    -capsule
    -cocci/rod/spirrilla/filamentous
    - <0.2um - >50um
  9. 9SHAPE AND SIZEcommon are
    - cocci
    - bacilli
    - curved
  10. 10CELL ENVELOPE- cell membrane
    - cell wall
    >> peptidoglycan (gram +ve)
    >> outer membrane(gram -ve)
  11. 11BACTERIAL CELL WALL : PEPTIDOGLYCAN- strength provided by one rigid layer composed primarily of peptidoglycan (PTG)
    - PTG layer is composed of repeating thin layers of sugar connected by peptides and amino acid crosslinks
  12. 12BACTERIAL CELL WALL- PTG can be destroyed by lysozome. breaks NAM - NAG bonds
    - destroys cell via osmotic lysis
    - found in body fluids (tears, saliva)
    >> If lysis does not occur, cell can survive as a protoplast with no PTG. eg mycoplasmas
  13. 13GRAM +VE CELL WALL : TEICHOIC ACID- Acidic polysaccharides embedded in cell wall of gram+ve bacteria
    - if associated with lipids = lipoteichoic acids
    - provide -ve charge of cell surface
  14. 14BACTERIAL OUTER MEMBRANE : GRAM -VE- additional layer found in gram -ve bacteria
    - composed of lipids and polysaccharides = liposaccharides (lps)
  15. 15BACTERIAL LPS- Lipid A component is often referred as endotoxin
    - As gram -ve bacterial dies, large amounts of endotoxin is released in the host, causing physiological effects
  16. 16GRAM STAIN PROCESS1. heat/dry
    2. crystal violet stain
    3. iodine fix
    4. alcohol de stain
    5. safranin stain
    = gram -ve is red
    = gram +ve is purple
  17. 17CAPSULE AND SLIME LAYERS- polysaccharide layer secreted on bacterial surface = glycocalyx
    > if rigid and exclude particles = capsules
    > if flexible = slime layer
    - role in attachment of pathogen to their host
    - provides protection against immune system
  18. 18BACTERIAL MOTILITY- the advantage of being motile is to allow bacterial to towards new resources (nutrients) or away from potentially hazardous ones.
  19. 19FLAGELLAlong thin appendages, attached to cell wall at one end and can be at various locations on cell surface.
  20. 20FLAGELLAR MOVEMENT- each flagellum is a semi-rigid structure
    - moves by rotation (propellar)
    - speed of rotation can be changed (motor)
    - movement related to the location of flagella
    1. POLAR -CCW rapid movement, straight line, CW tumbling
    2. Peritrichous - slowly in a straight line, release of flagella bundle, tumbling
  21. 21CONNECTION TO CHEMOTAXIS- directs bacterial movement in reponse to the chemical signal in the environment
    > attracted to the attractants such as sugar, amino acids
    > repelled by repellents such as toxins
    - in neural media, bacteria move randomly
    - when the environment contains an attractant , bacterial sense the concentration gradient of the attractant and move towards it
  22. 22CHEMOTAXIS- the peritrichous flagella on the bacteria twist together in order to push the bacteria forward from one side
    -the bundle flagella rotate together in a CCW direction
    >>This enables the bacteria to swim together and move in a straight line
  23. 23BACTERIAL FLAGELLA : IDENTIFICATIONMotility is a primary criterion for the identification of bacteria. techniques to demonstrate bacterial motility are
    1. flagellar stains - outline flagella and show their pattern of distribution
    2. Motility test medium - demonstrate if cells can swim in semi solid medium
    3. Direct microscopic observation - living bacteria in a wet mount shows transient movement of swimming bacteria
  24. 24FIMBRAE AND PILI- structurally similar to flagellar but not involved in motility
    > fimbrae - adhesion to surface; source of nutrients,formation of biofims, prevents flushing from host
    > Pili - conjugation; transfer of genetic material
  25. 25ENDOSPORES- dormant form of bacterium that allows it to survive at sub-optimal environmental conditions
    - have a tougher outer membrane made of keratin ; highly resistant to heat and chemicals
    - may be located central, sub terminal and terminal
  26. 26ENDOSPORE FORMATION- formed by vegetative cells in response to environmental signals that indicate a limiting factor in vegetative growth ; exhaustion of an essential nutrient
    - germinate and become vegetative cells when the environment stress is relieved
    - mechanism of survival rather than reproduction
  27. 27ENDOSPORE STAIN1. keratin coat resists staining, so specialised products are necessary
    2. malachite green stain is forced into spore by heating the cells
    3. vegetative cells are then decolourized with water (keratin layer stops malachite green getting out) and stained pink with safranin counterstain
  28. 28ACID FAST/ZEIHL-NEELSON STAIN-Mycobacterial cell wall contain waxy substance composed of mycolic acids
    - basic fuchsin binds to -vely charged groups in bacteria
    - mycolic acids present a barrier to dye entry
    - partly overcome by heating
    - staining.swf
  29. 29acid fast bacillired in colour
    - other components blue
  30. 30BACTERIAL CELL ENVELOPE1. Identification and epidemiological studies
    2. virulence determinants
    3. Diagnosis of disease
    4. Immunising antigens
  31. 31IDENTIFYING AND EPIDEMIOLOGICAL STUDIES- peptidoglycan influences gram stain
    - O- polysaccharide for serotyping : e-coli, salmonella
    - Capsule for serotyping : streptococcus, influenzae type B
    - Flagellae for serotyping: salmonella
  32. 32VIRULENCE DETERMINANTS- Capsule = antiphagocytic
    - Fimbrae = Adhesins
    - Outer membrane proteins = receptors for scavenged iron
  33. 33IMMUNISING AGENTScapsule

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Flashcards on MICROSCOPY & CELL MORPHOLOGY, created by Simmy Braich on 14/06/2014.
Created by
Simmy Braich · Jun 2014
Updated
Feb 19, 2016
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