Week 1: Basics of Bacteria

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jlyip89
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256380
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Week 1: Basics of Bacteria
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2014-01-18 22:23:48
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Bacteria
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Micro
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Micro: Week 1 Lecture
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  1. Important Facts about bacteria:
    - More bacteria cells on the body than our own cells

    - <0.01% of bacteria cause disease

    - Microbial infections are the most epidemic diseases and the leading cause of death worldwide (30 million death in 2010)

    - To understand the disease they cause and the ways to control them
  2. Locations of the body where bacteria will cause disease (5)
    • 1. Blood
    • 2. brain
    • 3. kidney
    • 4. lung
    • 5. liver
  3. 3 Different types of morphology of bacteria
    • - coccus (spherical)
    •      * single, chained, or clustered
    • - bacillus (rod)
    • - spiral (curved rod)
    •      * vibrio, spirochete
  4. colony

    - what is it?
    - contains?
    - descendants of?
    - how do diff. colonies vary?
    - clump of bacteria growing on the surface of solid medium (agar plate)

    – contain millions of bacterial cells

    – descendants of a single cell

    • – vary in texture, color, size, shape, odor, elevation, pigmentation, effect on growth
    • medium, way they adhere to surface, etc
  5. how can colony morphology be useful?
    Colony morphology can be useful in bacterial identification
  6. definition of basic vs. specialized bacterial structure
    basic cell structures are found in ALL bacteria

    specialized structures are found only in certain groups of bacteria
  7. List 5 basic bacterial cell structures
    – cell wall

    – cell (plasma) membrane

    – chromosome (nucleoid)

    – ribosomes

    - Inclusion (granule)
  8. List 6 specialized bacterial cell structures
    • – flagellum
    • – fimbria
    • – pilus
    • – glycocalyx
    • – plasmid
    • – spore (endospore)
  9. Name three architectural regions of bacterium
    • 1. appendages (attachment to cell surface)
    • 2. cell envelope
    • 3. cytoplasm
  10. Name the 3 types of Appendages
    • 1. Pilus
    • 2. Flagellum
    • 3. Fimbria
  11. Pilus

    - properties
    - function?
    • Properties:
    • - Longer than fimbriae
    • - An elongated, hollow appendage

    • Function:
    • transfer of DNA from one cell to the other (conjugation)

    - aka F pilus or sex pilus
  12. Fimbria

    properties?
    function?
    • properties:
    • - Thin, short, hair-like appendages
    • Vary in length
    • – Extend from entire surface of cell

    • Function:
    • Attachment to other bacteria or to the host target cells

    • Enables the cells to colonize
    • - Enhances the bacteria’s ability to cause disease  
  13. Flagellum

    - properties?
    - function?
    • properties:
    • - Specialized appendage
    • - attached to cell membrane
    • - long rotating filament
    • – Long, thick, thread-like appendage

    • function:
    • - provides motility
    • - Chemotaxis- movement toward nutrients, away from harmful chemicals

  14. Flagellum Structure (3 parts)
    1. Filament: long, thin, helical structure composed of proteins

    2. Hook: curved sheath

    3. Basal body: stack of rings firmly anchored to cell wall and membrane
  15. Name the 4 diff. Flagella arrangements

    - which flagella arrangement provides the slowest motility?
    1. Monotrichous: a single flagellum at one end

    2. Lophotrichous: clusters of flagella at one end

    3. Amphitrichous: a flagellum at each end

    4. Peritrichous: flagella distributed over the entire surface of the cell

    * Peritrichous provides the slowest motility bc the abundance of flagella causes more resistance(?)
  16. Name 2 Bacterial Movements
    • 1. Run
    • - forward movement
    • - counterclockwise rotation of the flagellum

    • 2. Tumble:
    • -  random tumbling motion
    • - helps change direction
    • - clockwise rotation of flagellum
  17. 3 components of bacterial cell envelope
    (order form outer to inner)

    • 1. glycocalyx 
    • 2. cell wall
    • 3. cell (plasma) membrane
  18. Glycocalyx

    - properties?
    - 2 types?
    • Properties:
    • - A coating or layer of molecules external to the cell wall

    – Jelly-like layer secreted by cell

    – Adheres to cell wall

    • –usually polysaccharide (sometimes proteins, e.g., B. anthracis)

    • types:
    • 1. Slime layer: thin layer, loosely organized, irregular

    2. Capsule: thick layer, highly organized, regular

    * not required for bacterial growth
  19. Glycocalyx Functions
    Attachment and protection!

    –allows bacterium to adhere to surfaces in their environment or to each other (colonization)

    protects bacterium from engulfment by phagocytes(antiphagocytic activity)

    protects bacterium against drying

    protects bacterium from attack by antimicrobial agents
  20. What stain do you use to visualize glycocalyx under the microscope?
    Glycocalyx visualized by Indian ink stain under light microscope
  21. Cell Wall
    •Extremely complex

    •Cell wall components are unique to bacteria

    •Provide structural support and osmotic barrier

    •Major target for antibiotics

    •Contain virulence factors

    • Contain antigens useful in serodiagnosis and classification
  22. Gram staining
    an empirical method of differentiating bacterial species into two large groups based on the chemical and physical properties of their cell wall
  23. Gram Staining Steps
    • 1. staining (Crsytal violet)
    • 2. fixing (Iodine)
    • 3. decolorization (alcohol/acetone)
    • 4. counterstaining (Safranin)
  24. Two groups of bacteria based on Gram stain
    Gram-positive cells appear blue-black/purple

    Gram-negative cells appear red/pink

    • *Diff color due to diff property (thickness of peptidoglycan) of the cell wall

  25. Gram Positive Cell wall

    - consists of
    thick layer of peptidoglycan

    tightly bound acidic polysaccharides, including teichoic acid and lipoteichoic acid
  26. Peptidoglycan

    - what is it?
    - structural components?
    - unique to bacteria (present both in Gram + and -)

    - principle compound of cell wall

    - Subunit of peptidoglycan is composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), and tetrapeptide attached to NAM

    - Peptidoglycan layer is a repeating subunit of peptidoglycan, forming a mesh-like layer outside the cell membrane
  27. peptidoglycan function
    - arrangement of peptidoglycan is responsible for rigidity and porosity of bacteria
  28. Teichoic and lipoteichoic acids

    - similarities
    - differences
    • similarities:
    • - present only in Gram +

    - important factor in virulence

    – play role in attachment (promote attachment to other bacteria and to specific receptors on mammalian cell surfaces; adherence)

    –essential to cell viability

    • Differences
    • - site of attachment:
    • – Teichoic acids attach to peptidoglycan

    – Lipoteichoic acids attach to cell membrane
  29. Periplasmic space (periplasm)

    - gram +
    - gram -
    - function
    • Gram +
    • - has 1 periplasmic space
    • - space btwn cell wall and cell membrane

    • Gram -
    • - has 2 periplasmic space:
    •     1. btwn cell wall and cell membrane
    •     2. btwn cell wall and outer membrane

    • function
    • - active compartment of the cell
    • - contains a variety of enzymes, e.g.,

    b-lactamase, an enzyme responsible for degrading the penicillin group of antibiotic drugs, leading to penicillin resistance.
  30. Gram (-) cell wall

    - consists of?
    – thin layer of peptidoglycan

    – outer membrane containing lipopolysaccharide (LPS) and porins

    *LPS is only specific to gram negative bacteria
  31. Outer membrane

    - structure
    - function
    - unique to Gram (-)

    • - asymmetric bilayered structure:
    •        * outer lipopolysaccharide layer
    •        * inner phospholipid layer

    - first and foremost permeability barrier to large molecules (e.g., proteins such as lysozyme) and hydrophobic molecules

    - provides protection from adverse environmental conditions
  32. lipopolysaccarides (LPS)

    - location?
    - composed of?
    - embedded in the outside layer of the outer membrane, only found in Gram (-)

    • composed of :
    • Lipid A: anchor molecule in outer component of outer membrane; toxic!

    Core polysaccharide: series of sugars constant for a given species

    O antigen: long repeating 3-5 sugar units,  responsible for antigenic diversity

    • •LPS, also called endotoxin, is toxic to animals
    • (Lipid A).
  33. LPS function
    LPS is a powerful inducer of immune response and coagulation factor, leading to fever, sepsis and shock


    LPS very TOXIC!
  34. Porins
    - Form pores in outer membrane, unique to Gram (-)

    - Act as protein channels for hydrophilic molecules less than 700 Da in mass through the membrane

    • - allows passage of metabolites and small hydrophilic antibiotics, but the outer membrane is a barrier for large or hydrophobic
    • antibiotics and proteins such as lysozyme
  35. Bacterial exceptions
    - Bacteria without cell walls (e.g. Mycoplasma)  cannot be stained for gram +/-

    – contain steroid from host cell
  36. Name some examples of bacterial w/ chemically unique cell walls

    - what surrounds its cell walls?

    - what stain should be used?
    • - Mycobacterium
    • - Corynebacterium
    • - Nocardia)

    –Cell wall surrounded by a wax-like lipid coat of mycolic acid

    - Determined by Acid fast stain (Ziehl-Neelsenstain)
  37. Acid fast stain (Ziehl-Neelsen Stain) Steps

    - when to use?

    - steps to staining?

    - color results?
    - for bacteria w/ high [ ] of lipids in their cell wall as they don't stain well with Gram stain

    • procedures
    • 1. staining (carbol fuchsin)
    • 2. Fixing (phenol)
    • 3. decolorization (acid/alcohol)
    • 4. counterstain (methylene blue)

    • Acid fast = pink/red
    • NOT acid fast = blue
  38. Diff types of Staining and cell wall composition
    • Gram positive: 
    • - 80% peptidoglycan
    • - multiple layers of peptidoglycan

    • Gram negative 
    • - 40% peptidoglycan & 40% lipids
    • - lipid layer outside
    • - thin peptidoglycan layer inside

    • Acid Fast
    • –20% peptidoglycan & 60% lipids (waxy)
  39. Properties of Cell (plasma) membrane
    most inner layer of cell envelope

    •thin, flexible membrane

    •most dynamic bacterial structure

    semipermeable (selectively permeable) membrane
  40. Cell (plasma) membrane structure and composition
    bilayer of phospholipids

    • structure of phospholipids
    • - Phosphate “head” - hydrophilic
    • - Fatty acid “tails” – hydrophobic

    – various proteins dispersed and embedded in the phospholipids bilayer
  41. Functions of cell membrane
    - Main selective permeability barrier that controls the movement of nutrients, wastes across the membrane

    - Location of various transport systems and specialized enzyme systems

    - Energy generating functions, involving respiratory and photosynthetic electron transport systems, and transmembranous ATP-synthesizing ATPase

    - Synthesis of membrane lipids (including LPS in Gram (-) cells) and peptidoglycan

    - Coordination of DNA replication and segregation with septum formation and cell division
  42. What component of bacterial cell structure do most antimicrobial peptides produced by the immune cells target?
    Cell membrane is the target of most antimicrobial peptides (e.g., defensins) produced by immune cells
  43. 3 components of the cytoplasm
    –chromosome (nucleoid)

    –ribosomes

    –inclusion (granule)
  44. Chromosome (nucleoid)
    • - Typically single, circular, double-stranded DNA molecule that contains all the genetic
    • information required by a cell

    • - DNA is highly folded, suspended in cytoplasm, aggregated in a dense area called the nucleoid

    - Lacks histones but has analogous structure, DNA gyrase
  45. Plasmids
    - only found in some bacteria

    - small circular, double-stranded ‘extra’-chromosomal DNA

    • - contain “special” genes that are not related to basic life functions
    •  * e.g., antibiotic resistance

    - duplicate and pass onto offspring

    - can be transferred from one bacterial cell to another

    - used in genetic engineering- readily manipulated & transferred from cell to cell
  46. ribosomes
    •consist of 2 subunits: large (50S) & small (30S)

    •involved in the process of translation (protein synthesis)

    diff. from host ribosome make it a target for some antibiotics
  47. Inclusions (granules)
    - intracellular storage bodies

    - vary in size, number & content

    - bacterial cell can use them when environmental sources are depleted

    • - examples of content :
    • glycogen, phosphate, inorganic ions, and gas for floating
  48. Spore (endospore)
    dehydrated, multishelled structure that enables bacteria to survive under harsh environmental condition

    • highly resistant to heat, radiation, attack by most enzymes and chemicals (spores are
    • used as indicators for sterilization assurance of medical supplies; spores can be used as biological weapons)

    • •With favorable conditions spore turns into vegetative cell

    • •Bacteria that form spores (called spore-formers) are all Gram-positive, but never Gram-negative
  49. Spore Formations Steps
    1. DNA is replicated

    2. DNA aligns along the cell's long axis

    3. Cytoplasm membrane invaginates to form forespore

    4. Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell's DNA disintegrates

    5. A cortex of calcium and dipicolinic acid is desposited btwn the membranes

    6. spore coat forms around endospore

    7. maturation of endospore; completion of spore coat and increase in resistance to heat and chemicals by unknown process.

    8. Endospore released from original cell
  50. Comparison of vegetative cells and spores contents:

    - calcium content ?
    - dipicolinic acid?
    - water content?
    - enzyme activity?
    - cytoplasmic pH?
    - macromolecule synthesis?
    • calcium content:
    • veg. low
    • spore high

    • dipicolinic acid:
    • veg: absent
    • spore:pressent

    • water content:
    • veg: 80-90%
    • spore: 10-25%

    • enzyme activity:
    • veg: high
    • spore: low

    • cytoplasmic pH:
    • veg: 7
    • spore: 6

    • macromolecule synthesis:
    • veg: present
    • spore: absent

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