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BS127: Agents of Infectious Disease > Microbiology (Lecture 1-8) > Flashcards

Microbiology (Lecture 1-8) Flashcards

1
Q

Why is Whittaker’s five kingdom tree wrong?

A
  • Oversimplifies the complexity of life on Earth
  • Does not account for evolutionary relationships b/w organisms
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2
Q

Why are there so many microorganisms?

A
  • Rapid growth rate
  • Many chances of speciation through random mutations
  • Lateral gene transfer (exchange of genetic material)
  • Every available niche is occupied by specifically adapted microbes
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3
Q

“Every available niche is occupied by specifically adapted microbes” explain this statement

A
  • Microbes hv been alive for so long thus
    • They’ve been in many places n adapted
    • Hence, can live in all these places
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4
Q

What are prototrophs?

A
  • Organism that synthesize all their own cellular components
    • Amino acids, nucleotides, vitamins
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5
Q

What are fastidious bacteria?

A

Bacteria that need organic components

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6
Q

Asexual reproduction in bacteria

A
  • Done by binary fission or budding
  • Cells double in size then split into two
  • Exponential growth bc 1 cell becomes 2 becomes 4
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7
Q

How do microbes grow?

A

Assimilating nutrients n cell division

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8
Q

Lag phase

A

Adapting to new conditions → takes some time for the organism to adjust

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9
Q

Log/exponential phase

A
  • Exponential growth
  • Once adapted, cells begin to grow n reproduce rapidly
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10
Q

Stationary phase

A
  • Limitation by nutrients, buildup of waste product that inhibit growth
  • Runs out of space n nutrients + waste build up → less growth n reproduction to occur
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11
Q

Death

A
  • Organisms start dying off n may lyse
  • Eventually will feed off dying cells
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12
Q

How can we measure bacterial growth?

A
  • Cell number
  • Optical density
  • Fresh/dry weight
  • Protein
  • DNA
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13
Q

What is the traditional way to identify microorganisms?

A
  • Microscopy n staining
  • Growth on selective/differential media
  • Testing substrate spectrum supporting growth
  • Characterization of cell chemical constituents
    • Lipids, cell wall components, DNA base ratio, quinones
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14
Q

Describe selective media

A
  • Allows the growth of only some types of organism
  • Used to culture/identify presumed pathogens from clinical specimens
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15
Q

Describe differential media

A
  • Allows the identification of organisms based on growth n appearance on that medium
    • Often based on colour differences
  • Used to determine whether a culture is potentially pathogenic
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16
Q

Describe the ApiZym test system for microbial identification

A
  • Culture of organism is grown
  • Cells resuspended in a buffer
  • Test wells are inoculated
  • Resulting colour in test strip is compared against database
  • Can help to distinguish between pathogenic n benign strains
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17
Q

What is an S-layer?

A
  • Regularly structured
  • Paracrystalline outer layer composed of protein or glycoprotein
  • External to cell wall in some bacterial n archaeal species
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18
Q

Function of S-layer

A
  • Protection against ion n pH fluctuations, osmotic stress n predators
  • Protect against host defenses
  • Sometimes act as a virulence factor
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19
Q

How did cellular life first evolve?

A
  • Surface origin hypothesis
  • Subsurface origin hypothesis
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20
Q

What is the surface origin hypothesis?

A
  • Warm little pond
  • Primordial soup (Evidence that organic molecules can form spontaneously)
  • Hypothesis unlikely due to hostile conditions on surface
    • High UV, meteor strikes, volcanic activity
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21
Q

Subsurface origin hypothesis

A
  • Hydrothermal vents at ocean floor
  • More stable conditions
  • Constant source of energy (reduced inorganic compounds)
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22
Q

Key features of the origin of cellular life

A
  • Self replicating RNA
  • Enzymatic proteins
  • DNA
  • Evolution of biochemical pathways
  • Divergence of lipid biosynthesis
  • Divergence of cell walls
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23
Q

Landmarks in biological evolution

A
  • Early life probably dependent on H2 n CO2 (fixed by bacteria)
    • Bacteria makes acetate
    • Archaea makes methane
  • Energy n carbon metabolisms diversif
  • Phototrophy, using H2S as electron donor
  • Evolved into an oxygenic photosystems using H2O
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24
Q

Characteristics of molecular sequences in phylogenetic analysis

A
  • Must be universal
    • Ribosomes, DNA, RNA
    • Contain variable n conserved regions
    • Not subject to HGT
    • Homologous (same purpose)
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25
Q

Why are ribosomal RNA genes a universal molecular marker?

A

Present in all forms of life

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26
Q

What are the potential chain of events in evolution of eukaryotes?

A
  • Endosymbiotic theory: acquisition of mitochondria
    • May hv led to the divergence of eukaryotes n archaea
  • Nucleus forms n separates itself in the cell → complex organelles form
  • Acquisition of cyanobacteria
    • Becomes a chloroplast
    • Produces lineage of plants capable of photosynthesis
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27
Q

Describe aquifex

A
  • Isolated from a hot spring
  • Hyper thermophilic
  • Chemolithoautotrophic
    • Oxides H2 to water using O2 as e- acceptor
  • Autotrophic
    • C-fixation
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28
Q

Describe deinococcus

A
  • Radiation resistant
  • Isolated from canned meat sterilized by gamma irradiation
  • V rapidly reassembles radiation damaged
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29
Q

Describe cyanobacteria and plastids

A
  • Blue green algae
  • Plastids were originally cyanobacteria
  • Morphologically diverse
  • Widely distributed
  • Oxygenic phototrophs
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30
Q

Describe chlamydia

A
  • Obligate intracellular parasites
  • Distinct life cycle
  • Important human pathogens
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31
Q

Describe spirochaetes

A
  • Helically shaped, motile, gram negative
  • Flagellum inside the cell
  • Heterotrophs
  • Contains free living, symbiotic n parasitic species
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32
Q

How are species defined in higher organisms?

A

Groups of individuals that can interbreed n produce viable offspring

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33
Q

Why is the definition of species in higher organisms problematic in microbiology?

A

Due to:

  • Asexual reproduction
  • Lateral gene transfer
  • Phenotypic n genotypic plasticity of microorganisms
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34
Q

Current definition of species in microbiology

A

Group of strains that show a high degree of overall similarity and differ considerably from related strain groups with respect to many independent characteristics

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35
Q

Describe the gram staining procedure

A
  1. Spread culture in thin film over a slide
  2. Dry the culture in air
  3. Pass slide through flame to fix culture to slide
  4. Staining process:
    1. Culture is flooded with crystal violet for 1 minute
      1. Cells turn purple
    2. Add iodine solution for 3 minutes (to wash out crystal violet)
      1. Cells remain purple
    3. Decolorize with alcohol briefly
      1. Gram-positive cells are purple
      2. Gram-negative cells are colorless
    4. Counterstain with safranin for 1 - 2 minutes
      1. Gram positive cells are purple
      2. Gram negative cells are pink to red
  5. Drop of oil is placed on the slide
    1. Examined under microscope
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36
Q

Why do gram-positive cells stain purple?

A
  • Hv thick cell wall w LPS layer
  • Crystal violet can bind to thick LPS layer
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37
Q

Why do gram-negative cells stain purple?

A
  • Thin walls
    • When washed w alcohol, thin cells hv their violet washed out [weak binding]
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38
Q

Biochemical test — decomposition of simple carbohydrates

A
  • Observing how microorganisms react to different types of carbohydrates under anaerobic or aerobic conditions
  • Glucose decomposed → acid produced → changes pH n induces a colour change in medium
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39
Q

Biochemical test — fermentation test

A
  • Identify the ability of microorganisms to produce acids (lactate n acetate) by fermenting sugars
  • Acid production results in a change in pH n can induce a color change in the medium
  • Gas production is collected in Durham tube n observed
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40
Q

How can the metabolic capabilities of microorganisms aid in their identification?

A
  • By identifying the metabolic pathways that are used by microorganisms, we can classify bacteria and determine their potential pathogenicity.
  • Different tests can be used to identify the presence of specific enzymes or the ability to decompose different substrates, providing important information about the microorganisms.
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41
Q

Psychrophiles

A
  • Inhabit permanently cold environments
    • Arctic, antarctic deep sea, glaceris
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42
Q

How do psychrophiles adapt to low temperature environments?

A

Modifying protein structure n membrane fluidity

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43
Q

What are hyper-thermophiles and where are they generally found?

A

Microorganisms that grow at temperatures above 80°C and are generally found in hot springs and thermal vents.

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44
Q

What is FAME analysis and how is it used in molecular analyses?

A
  • Determination of fatty acid profiles of membrane lipids
  • Used in molecular analyses by comparing the chromatograms of the extracted lipids and chemically modified methyl esters to a database for the best match.
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45
Q

What is AFLP and how is it used to distinguish closely related strains of bacteria?

A
  • Technique used to distinguish closely related strains of bacteria by targeting repetitive elements in the bacterial genome
  • It determines the number of repeats in a genome and compares the electrophoretic patterns of the results.
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46
Q

From outside to inside, what are the components of bacterial cells?

A
  • Capsule, S-layer
  • Then:
    • Gram positive bacteria
      • Cell wall
    • Gram negative bacteria
      • Outer membrane
  • Periplasmic space
    • With peptidoglycan in Gram –ves and some Gram +ves
  • Cell (plasma) membrane
    • Universal to all cells
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47
Q

Describe a capsule

A
  • Glycocalyx (sugar coat)
  • Polysaccharide components outside the cell wall
  • Loose network of polymer fibres extending outward from wall
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48
Q

Describe the capsule’s slime layer

A
  • Diffuse, unorganized, easily removed
  • Does not exclude small particles
  • Can be difficult to visualize
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49
Q

What are the roles of capsules?

A
  • Not required for growth/reproduction
  • Carbon store
  • Protection against desiccation
  • May be involved in the capture of nutrients
    • Acquisition of ions from the environment
  • Confer advantages in vivo
    • Attachment to surfaces
      • Biofilms, holdfast to eukaryotic cells
  • Exclude phage, antimicrobials and disinfectants
  • Pathogens often capsular and resist phagocytosis
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50
Q

What is the difference b/w a capsule n a slime layer?

A
  • Capsule: organized, tight matrix that is not easily removed, excludes small particles (e.g. India ink)
  • Slime layer: diffuse, unorganized layer that is easily removed n does not exclude small particles
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51
Q

What are bacterial adhesins?

A
  • Allow cells to stick to n attack other cells
  • Includes capsular polysaccharides, EC slime, fimbriae n lectins
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52
Q

Describe an S-layer

A
  • Generally not associated w pathogens
  • Paracrystalline outer wall layer composed of protein/glycoprotein
  • Regularly structured layer external to cell wall
  • May protect against ion and pH fluctuations, osmotic stress, predators such as Bdellovibrio
  • May protect against host defenses
    • Sometimes a virulence factor
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53
Q

What is the composition of peptidoglycan in both Gram-positive and Gram-negative bacteria?

A

Alternating residues of NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid)

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54
Q

How are the NAG and NAM residues arranged in peptidoglycan?

A

Cross-linked by amino acid side chains creating amide bonds

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55
Q

What is the function of peptidoglycan in Gram-positive bacteria?

A

Forms a mesh-like polymer that retains Gram stain

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56
Q

What are the non-protein amino acids found in peptidoglycan?

A
  • D-glutamic acid
  • D-alanine
  • DAPA
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57
Q

How do D-amino acids protect peptidoglycan from degradation by proteases?

A

Proteases typically break down proteins that use L-amino acids

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58
Q

Why does the capsule use D-amino acids?

A

D-amino acids cannot be broken down by proteases

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59
Q

Peptidoglycan structure

A
  • Chains of linked peptidoglycan subunits
  • Joined by cross-links between the peptides
  • Cross-links often occur between carboxyl group of terminal D-alanine and amino group of diamino pimelic acid (DAPA)
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60
Q

What is the function of peptidoglycan?

A
  • Provides structural support and shape to bacterial cell walls
  • Porous, elastic, and stretchable
  • Strong enough to retain shape when isolated
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61
Q

What are the cross-links in peptidoglycan synthesis for E. coli and Staphylococcus aureus?

A
  • E. coli: Cross-links between DAPA and D-alanine
  • Staphylococcus aureus: Cross-links between L-lysine and glycine
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62
Q

How are peptidoglycan chains cross-linked to form a solid structure?

A
  • Peptidoglycan chains form sheets
  • Sheets are cross-linked with each other to form a solid-like structure
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63
Q

Lysozyme

A

Antibacterial enzyme that degrades β, 1-4 glycosidic bonds in peptidoglycan backbone

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64
Q

What does the loss of PG lead to?

A

Makes bacterial cells sensitive to changes in osmotic pressure → cells more likely to burst

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65
Q

Lysozyme function

A
  • Host defense against bacteria
  • Present in saliva, tears and secreted in airways
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66
Q

How does penicillin halt cell wall synthesis?

A
  • Inhibits peptidoglycan synthesis
    • Targets transpeptidation step (pencilin sensitive)
  • Transpeptidation: involves cleaving 1 of the 2 D-Ala residues in the linker peptide n linking it to DAPA (-) or L-Lys (+)
    • Penicillin prevents this → cells become osmotically sensitive n lyse
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67
Q

Why is penicillin more effective for gram positive bacteria?

A

Gram negative doesn’t depend on peptidoglycan as much as the gram positive

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68
Q

How do archaeal cell walls differ from bacterial cell walls?

A
  • Archaeal cell walls lack:
    • Peptidoglycan/murein
  • Archaeal cell walls contain:
    • Pseudomurein
    • Other polysaccharides or glycoproteins
    • S-layers
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69
Q

What is pseudomurein and how is it different from peptidoglycan/murein?

A
  • Structural component found in some methanogenic archaea
  • Similar to peptidoglyan/murein
    • Composed of alternating NAG n NAT subunits
  • Linked by β 1,3 instead of β 1,4 glycosidic bonds
  • Lacks D-amino acids in linker
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70
Q

Why are archaeal cell walls not susceptible to degradation by lysozyme or inhibition by penicillin?

A

Archaeal cell walls lack the specific structural features (peptidoglycan/murein, D-amino acids in the linker) that are targeted by lysozyme and penicillin in bacterial cell walls, making them resistant to these agents.

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71
Q

Role of sterols/hopanoids in membranes

A
  • Stabilize membrane structure
  • Make membrane more rigid
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72
Q

Difference between hopanoids n sterols

A
  • Hopanoids
    • Bacteria
    • Rigid, planar molecules
  • Sterols
    • Eukaryotes
    • Flexible
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73
Q

Are hopanoids found in archaea?

A

No, instead hv isoprene structures

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74
Q

How do hopanoids and sterols respond to a rise in temperature?

A

Stabilize membranes

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75
Q

Why is the outer membrane of Gram-negative bacteria asymmetric?

A

Insertion of LPS into external layer of outer membrane

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76
Q

What is Braun’s lipoprotein?

A

Protein that is covalently linked to peptidoglycan n embedded in OM of gram negative bacteria by hydrophobic end

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77
Q

What is the function of Braun’s lipoprotein in the outer membrane of Gram-negative bacteria?

A
  • Attaches peptidoglycan layer to OM n serves as an adhesion site for 2 membranes
  • Allows transport of substances b/w membranes
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78
Q

How can adhesion sites between the inner and outer membranes be visualized?

A
  • Induce plasmolysis → increase space b/w membranes
  • Transmission electron microscopy (TEM)
  • Immunogold staining → used to track viral particles entering cell thru adhesion sites
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79
Q

What is the significance of adhesion sites in Gram-negative bacteria?

A
  • Structural integrity of Gram-negative bacteria by attaching peptidoglycan layer to OM
  • Allows transport of substances b/w membranes
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80
Q

Describe the structure of lipopolysaccharide (LPS)

A
  • Lipid A
  • Core polysaccharide
  • O side chain
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81
Q

What can LPS induce when it interacts with the innate immune system?

A

Massive immune response (septic shock)

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82
Q

Describe lipid A

A
  • 2 glucosamine residues linked to fatty acids and phosphate (occasionally pyrophosphate)
  • Lipid A is integrated into outer membrane
    • Immunogenic
  • Remaining LPS projects from cell surface
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83
Q

Describe core polysaccharide

A
  • AKA R-antigen or R-polysaccharide
  • Side chain of NAG, phosphate and ethanolamine
84
Q

Describe O side chain

A
  • Variable region → responsible for antigenic make-up of bacteria
  • Flexible n bent
  • Highly variable composition
  • R/S variants depend on side chain length
85
Q

Functions of LPS

A
  • Lipid A stabilizes outer membrane structure
  • Core polysaccharide charged
    • Contributes to negative charge on surface
  • Charged, hydrophilic external layer → reduces permeability of hydrophobic substances
    • Prevents entry of bile salts, antibiotics
  • Protects against host defences
    • Rough variants are more susceptible to phagocytosis
    • Loss of O-antigen in E.coli and Salmonella → reduced virulence
  • O-antigen v variable → key diagnostic tool
86
Q

What is endotoxin?

A
  • Molecule that can be released during the growth or lysis of bacterial cells
  • Composed of LPS
87
Q

When is endotoxin released?

A

During cell division or by lysis of bacterial cells

88
Q

What happens when LPS is in the blood?

A

Causes septic shock syndrome

89
Q

How to test for endotoxin?

A
  • Rabbit pyrogen test
  • LAL assay
90
Q

Function of endotoxin

A

Prime to immune system against a pathogen, preparing it to act again by becoming aware of the antigen

91
Q

Describe Limulus Amaebocyte Lysate (LAL) test

A
  • Amaebocytes: blood cells of Limulus polymephus
  • Contains a clotting factor that’s released if comes in contact w bacterial endotoxin
  • Natural immune mechanism that contains bacterial infection
92
Q

Properties of endotoxins

A
  • Heat stable
  • Toxic in nanogram amounts
  • Interacts w innate immune system cells
    • Can trigger cytokines release in a cascade
    • Activates transcription factors (e.g. interferon-beta n tumour necrosis factor)
93
Q

Endotoxin can result in

A
  • Inflammation
  • Fever
  • Vasodilation
  • Thrombosis
94
Q

What are porins?

A

Protein channels that permit passage of small molecules up to around 600 Da

95
Q

How do larger molecules cross the outer membrane?

A
  • By attaching to carriers n passing through active transport systems
  • NOT accomplished through porins
96
Q

What is the porin superfamily?

A
  • Homotrimeric, transmembrane proteins that form water-filled channels in the OM
  • Highly conserved structure
    • Similar amino acids involved in binding n transferring molecules across the membrane
97
Q

What is the selectivity of most porins?

A
  • Slightly cation selective → prefer to move cations
  • Non-specific channels that allow the passage of small (<600 Da) hydrophilic molecules
98
Q

Are all porins non-selective?

A
  • Some porins are selective
    • E.coli LamB is a maltose n maltodextrin selective porin that was first identified as the receptor for bacteriophage Lambda
99
Q

Porin structure

A
  • Common β strand structure
    • 16 stranded anti parallel β-barrel
  • Unusual structure is exceptionally stable → produces essentially closed structure
100
Q

Why are porins important for the survival of Gram-negative bacteria in harsh environments?

A
  • High thermal stability
  • Resistant to protease n detergent degradation
101
Q

How are porins stabilized?

A

Formation of a salt bridge b/w N- n C- termini → provides extra stability to the structure

102
Q

What is the oligomeric state of porins?

A

Trimers

103
Q

What is the shape of a porin monomer?

A
  • Hourglass shape w a central constriction
  • Has a hydrophobic of 25A that sits in the membrane
104
Q

What dictates the size of the solute that can traverse the channel in porins?

A
  • Charges inside the pore of porins
    • Also dictate what species can go thru the porin
105
Q

What is the periplasmic space?

A

Space b/w the OM n the cytoplasmic membrane in gram-negative bacteria

106
Q

What is the gel-like consistency of the periplasmic space due to?

A

Abundance of proteins

107
Q

What is the function of hydrolytic enzymes such as alkaline phosphatase in the periplasmic space?

A
  • E.g. alkaline phosphatase
    • In periplasmic space
    • Strip phosphate from any molecule it sees → providing phosphate for IC usage
108
Q

How do some enzymes in the periplasmic space contribute to energy conservation in bacteria?

A
  • E.g. electron transport
  • Transport them thru inner membrane
109
Q

What is the function of peptidoglycan synthesis enzymes in the periplasmic space?

A
  • Located in the periplasmic space
  • Responsible for synthesizing peptidoglycan in that area
110
Q

What is the role of periplasmic binding proteins in bacterial cells?

A
  • Periplasmic binding proteins deliver specific compounds to ABC transporters in the cytoplasmic membrane
  • Facilitates the uptake of nutrients by bacterial cells
111
Q

What is the function of chemoreceptors located in the periplasmic space?

A
  • Detect changes in the chemical environment
  • Transmit signals to the cytoplasmic membrane to direct bacterial movement
112
Q

Where do chemoreceptors sit in Gram-negative bacteria?

A

Surface of the inner membrane in gram-negative bacteria

113
Q

What is the Sec pathway?

A
  • Nascent polypeptides are transported from the inside of the inner membrane to periplasmic membrane space in bacteria
  • Ribosomes on inside of inner membrane synthesize polypeptides n the Sec protein exports them thru the cytoplasmic membrane using a translocase
114
Q

How does protein folding occur in the periplasmic space?

A

After the nascent polypeptide has been transported there thru the Sec pathway

115
Q

What is the TAT pathway in bacterial protein export?

A
  • Fully folded enzymes are exported across the cytoplasmic membrane in bacteria
  • Polypeptides hv a twin-arginine in the N-terminal region
    • Acts as a signal to go thru the TAT pathway
116
Q

How does the TAT pathway differ from the Sec pathway in bacterial protein export?

A
  • TAT: exports fully folded enzymes
  • Sec pathway: exports nascent polypeptides that fold after translocation into the periplasmic space
  • TAT pathway also requires a different single peptide than the Sec pathway
117
Q

What is the role of the translocase in the Sec pathway of bacterial protein export?

A

Transporting nascent polypeptides across the cytoplasmic membrane n into the periplasmic space

118
Q

What are the 3 different transport types across the CM?

A
  • Simple transport
  • Group translocation
  • ABC system
119
Q

Describe simple transport

A
  • H+ transported down the concentration gradient
  • Energy used to transport another substance
120
Q

Describe group translocation

A
  • Higher concentration of substance outside of the cell
  • Substance transported down gradient
  • Addition of phosphate to transported substance
  • Prevents change in concentration gradient
  • Molecules can still diffuse down concentration gradient
121
Q

Describe ABC system

A
  • Takes component to transporter
  • Transports components
  • ATPase → uses hydrolysis energy to transport
122
Q

What are flagella?

A
  • Long, thin EC helical structures
  • Made of protein subunits that aid in motility
  • Connected to a motor that spins them clock or anti-clockwise allowing bacteria to swim and change direction
123
Q

Describe the structure of a flagellum

A
  • Long, thin, EC helical structure made of protein subunits that aid in motility
  • Connected to a motor that spins them clock or anticlockwise
    • Allows bacteria to swim n change direction
124
Q

What is the motor of the flagellum?

A

Driven due to proton transfer thru ring structure (from periplasm to cytoplasm)

125
Q

What happens when the flagella fall off?

A
  • If the flagella falls off, motility is lost
  • Rings n hook of flagellum are rigid n attached to the membrane n cell wall/OM
  • Flagellum shaft is easy removed by vigorous shaking
126
Q

Describe flagella synthesis

A
  • Flagella synthesis starts with the MS and C rings in the cytoplasmic membrane
    • Form the motor proteins for the flagellum.
  • The P and L rings, hook, and cap are assembled next in the periplasm.
  • Flow of flagellin monomers through the channel in the hook leads to growth of the filament at the tip.
  • Once assembled, the flagellum is anchored to the cell wall and outer membrane through complex ring structures.
  • The flagellum constantly grows to repair shear damage caused by movement, and can be removed by vigorous shaking.
127
Q

How does the motor work?

A
  • Rotary motion provided by basal structures
    • This mechanism is not completely understood
  • Powered by proton motive force
    • Protons move across the cytoplasmic membrane thru the MOT complex
128
Q

What is the mot complex?

A
  • Collection of proteins in the bacterial cytoplasmic membrane that forms the basal structure of the flagellum motor
  • MotA n MotB (2 integral membrane) interact to create a channel for protons to flow across the membrane
  • Flow of protons thru the channel generates a torque that drives flagellum rotation
129
Q

What is the role of Asp residue in MotB in the motor?

A
  • Mutational analysis suggests dependence on an Asp residue in MotB
  • Hypothesis: Changes in charge lead to conformational change of MotA, causing movement relative to MotB
  • Second conformational change upon loss of charge may provide another step of the motor
130
Q

Describe bacterial movement - run

A
  • Motor rotates anti-clockwise
  • Flagellar filaments (w LH helices) form bundle n propels cell
131
Q

Describe bacterial movement - tumble

A
  • Quick reversal of motor to clockwise rotation
  • Produces twisting force that transforms flagella into a right-handed helix
  • Causes bundle to fall apart rapidly
132
Q

How do separated filaments act?

A

In an uncoordinated way to generate forces that change cell orientation

133
Q

Aerotaxis

A

Towards oxygen

134
Q

Chemotaxis

A

Towards nutrients, away from toxins

135
Q

Magnetotaxis

A

Movement along the lines of magnetism

136
Q

Phototaxis

A

Towards light

137
Q

How does bacteria sense a change in nutrient concentration in the environment?

A
  • Transmembrane proteins
    • MCP: detect n measure changes in the environment
138
Q

How do MCPs control movement?

A
  • Interact w cytoplasmic membrane, which interact w the rings of the motor that regulate the direction in which it turns
  • Dictates run or tumble by a switch from anti-clockwise to clockwise rotation
139
Q

What are transducer proteins?

A

Another name for MCPs (act as receptors that detect certain molecules)

140
Q

What happens when an attractant binds to an MCP?

A
  • Attractant binds to MCP
  • Decrease in activity of sensor kinase CheA
  • RESULT: less phosphorylation n kinase activation
141
Q

What happens when a repellent binds to an MCP?

A
  • Repellent binds
  • Increase in activity of CheA
  • RESULT: more phosphorylation and activation of the kinase
142
Q

What is the role of CheA in bacterial chemotaxis?

A
  • Sensor kinase that can autophosrylate
  • Activated
    • Initiates a signaling cascade that results in the regulation of the direction of flagellar rotation in the bacterium
143
Q

How do MCPs interact with CheA in bacterial chemotaxis?

A
  • Binding of attractants or repellents to MCPs modulates the activity of CheA
    • Leads to changes in the direction of flagellar rotation n dictates the bacterium’s movement
144
Q

How do MCPs detect signals?

A
  • When MCP binds, they undergo a conformational change
    • This change is transmitted to the cytoplasmic domain of the protein
  • Domain interacts w signaling pathway that regulates the flagellar motor’s rotation
  • Interaction b/w MCP n signaling pathway is modulated by CheA
    • Two results: phosphorylated or dephosphorylated
  • Allows the bacteria to regulate their movement in response to changes in the environment
145
Q

What is the role of CheY in bacterial chemotaxis?

A
  • Cytoplasmic protein that is phosphorylated by CheA-℗
    • Response to signals detected by MCPs
  • CheY-℗ (not CheY) can bind to flagellar motor n change the rotation from CCW to CW → tumbles
146
Q

What is the role of CheZ in bacterial chemotaxis?

A
  • Phosphatase that dephosphorylates CheY-℗
  • Allows the CCW motion to resume n bacterium to continue running
147
Q

How do attractants and repellents affect bacterial chemotaxis?

A
  • Attractants → decrease CheY-℗ → less switching n longer runs
  • Repellents → increase CheY-℗ → more tumbling
148
Q

What is the adaptation in chemotaxis?

A
  • Bacteria integrate signals from attractants or repellents over time via methylation of MCP
    • CheR constantly methylates MCP
  • Allows the cell to become less sensitive to a signal that is present for a long time
    • Fully methylated MCP is insensitive to attractant
    • If attractant binds to fully methylated MCP → nothing happens
149
Q

How is MCP methylation regulated in bacterial chemotaxis?

A
  • Regulated by CheR n CheB
    • CheR: constantly methylates MCP
    • CheB: methylesterase that is phosphorylated by CheA-℗ → increases methylesterase activity → demethylates MCP
  • Low conc of attractant → high conc of CheA-℗ n CheB-℗ → demethylation of MCP → increasing sensitivity to the attractant → longer runs
  • High conc of attractant → low CheA-℗ n CheB-℗ → high methylation lvl of MCP → decreasing sensitivity to the attractant + increasing autophosphorylation of CheA → making it more likely to tumble
150
Q

What is the role of methylation of MCP in chemotaxis?

A

Methylation of MCP desensitises the cell to a specific concentration of attractant or repellent and serves as a bacterial “memory” of previous exposures.

151
Q

How does methylation of MCP affect bacterial behavior in high concentrations of attractant?

A

In high concentrations of attractant, MCP is methylated (more cheA-℗), resulting in shorter runs and tumbling to stay in a “good” environment.

152
Q

How does methylation of MCP affect bacterial behavior in high concentration of repellent?

A

In high concentration of repellent, MCP is methylated (less cheA-℗), resulting in longer runs and less tumbling to leave a “bad” environment.

153
Q

What is the significance of the bacterial “memory” in chemotaxis?

A

The bacterial “memory” allows the cell to alter its behavior to changing environments based on previous exposures, which increases its chances of survival and efficient use of resources.

154
Q

Gliding motility in Flavobacterium johnsoniae

A
  • Without flagella
  • Bacterium secretes slime n glides across the surface
155
Q

What is the mechanism of gliding motility in F. johnsoniae?

A
  • Adhesive molecules move laterally along the cell surface during gliding
  • Suggests a tank wheel like mechanism
156
Q

What are the Gld proteins involved in gliding motility?

A
  • 8 Gld proteins in total
  • 3 of them are components of an ABC transporter
  • 5 are lipoproteins located in the cytoplasmic / OM
157
Q

What happens when gld genes are disrupted?

A
  • Loss of motility
  • Increased resistance to bacteriophages that infect wild type cells
  • Loss of the ability to digest the insoluble polysaccharide chitin
158
Q

What is the mechanism of twitching motility via type IV pilus?

A
  • Based on the pili first extending from the cell surface then being retracted, dragging the cell along the surface
  • Process is powered by ATP hydrolysis
  • Throws out pilsu n use it to pull itself along
    • Like a grappling hook
159
Q

Why do protein vesicles contain gas?

A
  • Confers buoyancy to the cell
  • Allows cell to float up to oxygenated water/towards the light
  • Involved in vertical migration in aquatic systems
160
Q

Is the ability to produce ß-galactosidase and indole from tryptophan necessary for a bacteria to be classified as E. coli?

A

By definition, E. coli produces the enzyme ß-galactosidase and produces indole from tryptophan at 44°C. Knocking out these abilities through single mutations could mean that the bacteria is no longer considered E. coli. This is an important consideration for bacterial classification.

161
Q

Role of fimbria/pili

A
  • Loose association
  • Adhesion, role for pili/fimbriae
  • Invasion into or thru submucosal epithelial cells
162
Q

Explain how fimbria/pili assisted adhesion

A
  • Pili establish contact w host cell using its adhesive tip protein
  • host cell surface and bacterial surface are (-)vely charged
  • pili sticking out of bacterial surface to avoid electrostatic repulsion
  • resist flushing by moving contents of intestine/urine
  • pilus’ adhesive tip protein binds to a receptor that’s usually a glycolipid or glycoprotein
  • pili depolymerise
    • pulls bacterium close to host cell
    • additional adhesins bind to host cell
  • colonisation can begin
163
Q

What is the Type 1 fimbriae and where is it found?

A
  • Thin surface polymer
  • Well-characterized n widespread in Enterobacteriaceae, including most E. coli
  • Important virulence factor in a range of pathogens
164
Q

Describe the structure of the Type 1 fimbriae

A
  • FimH: tip adhesin
    • Binds to structures containing D-mannose
  • FimF n FimG link FimH adhesion onto fimbriae
165
Q

Function of FimD usher protein in Type 1 fimbriae assembly

A
  • FimD → usher protein
    • Catalyzes Fim A polymerization at base of pili
166
Q

Which pathogens use the chaperone-usher pathway to assemble their pili/fimbriae?

A
  • E.coli
  • Salmonella spp
  • Vibrio cholerae
167
Q

What is the role of FimC in the assembly of Type 1 fimbriae?

A
  • Chaperone protein
  • Plays a critical role in the assembly of Type 1 fimbriae
  • Helps in the proper folding n stabilization of FimA subunits, which are the building blocks of Type 1 fimbriae
168
Q

What happens without FimC in terms of the assembly of Type 1 fimbriae?

A

Subunits may misfold n become unstable, resulting in the assembly of non-functional or defective fimbriae

169
Q

What are P-pili and what is their function?

A
  • Critical virulence factors of UPEC
    • Causes cystitis n pyelonephritis
  • Involved in adhesion to glycolipids on uroepithelial cells
170
Q

What is pyelonephritis and why is it dangerous?

A
  • Urinary tract infection that reaches the kidneys
  • Can be dangerous n fatal if not treated properly
171
Q

How are P-pili structured and assembled?

A
  • Structure n assembly similar to that of type I fimbriae
  • Consist of a helical cylinder composed of many protein subunits
    • PapG as tip adhesin
172
Q

What is the function of PapG in P-pili?

A
  • Tip adhesin of P-pili
  • Binds to surface globoside receptors (glycolipids) in uroepithelial cells → allowing the bacteria to attach n invade the host cells
173
Q

What are the variants of PapG and what do they bind to?

A
  • 3 variants of PapG: PapG1, PapG2, PapG3
  • Bind to surface globoside receptors on eukaryotic cells, allowing the bacteria to adhere to n infect the host
174
Q

What are Type IV pili and where are they found?

A
  • Thin n flexible fibres
  • Found in some Gram-positive bacteria
    • Clostridia
175
Q

How are Type IV pili different from fimbriae?

A
  • Typically longer than fimbriae
  • Only present in a few numbers per cell
  • Typically found at both cell poles n are often not hollow like flagella
176
Q

What are the roles of Type IV pili?

A
  • Host cell adhesion
  • Biofilm formation
  • Twitching motility
177
Q

What is twitching motility?

A
  • Form of movement in bacteria that is powered by ATP hydrolysis n controlled by retraction proteins
  • Important for bacterial colonization n pathogenesis
178
Q

What is the relationship between bundling and virulence in Type IV pili?

A
  • Can aggregate laterally to form bundles
  • Bundling mutants, which lack the ability to form these bundles, hv reduced virulence
179
Q

What is the specificity of E.coli pathogens determined by?

A
  • LPS (O antigen) and fimbriae (K antigen)
    • CFA (colonising factor antigen) fimbriae are present on E. coli pathogenic to humans
180
Q

What is the specific interaction between Enterotoxigenic E. coli (ETEC) strains and mucosal epithelium?

A

Interacts w mucosal epithelium thru a surface antigen called CFA (colonizing factor antigen)

181
Q

Role of CFA in E.coli

A
  • Factor pathogenic to humans
  • Allows ETEC strains to adhere to the mucosal epithelium, facilitating their colonization n infection
182
Q

Where do pathogenic strains of E. coli adhere?

A
  • Adhere to tissues other than the colon where they express their pathogenicity by producing toxins
    • E.g. small intestine n urinary tract
183
Q

Role of F plasmid in gene transfer

A

Enables the transfer of genetic material (e.g. plasmids) b/w bacterial cells

184
Q

How does the F pilus facilitate adhesion and information transfer?

A
  • Acts similar to Type 4 pili in adhesion
  • Attaches to another cell via its tip
  • Retracts to bring the cells together
  • Once attached, initiates the transfer of genetic information b/w the cells
185
Q

What is the process of pilus-mediated gene transfer between an F+ donor and an F- recipient?

A
  • F+ donor (carries F plasmid) forms a pilus
  • Pilus of F+ donor attaches to surface of the F-recipient cell
  • F+ pilus can only attach to an F- recipient
  • Once attached
    • Pilus contracts
    • 2 cells pulled together
  • 2 cell membranes fuse
    • Form bridge that connects 2 cells
    • Plasmid is replicated to the F-recipient cell
    • Plasmid is replicated to F-recipient cell
      • Sometimes other genes are transferred in the plasmid
186
Q

Purpose of bacterial endospores

A
  • Dormant stage in bacteria life cycle
  • Providing a survival mechanism for bacteria under unfavorable conditions
187
Q

Properties of bacterial endospores

A
  • Highly resistant to
    • Heat
    • Desiccation
    • Radiation
188
Q

How do bacterial endospores form?

A
  • Vegetative cell undergoes sporulation in response to stress or unfavorable conditions
  • Vegetative cell transforms into a format endospore (highly resistant)
  • Endospore remains inside the bacterial cell until the cell dies → releases the spore into the environment
189
Q

Which types of bacteria commonly produce endospores?

A
  • Soil bacteria
    • Bacillus
    • Clostridium
    • Sporosarcina
  • Only gram-positive bacteria hv the ability to produce endospores
190
Q

How do endospores contribute to bacterial survival?

A
  • Highly resistant
    • Enable bacteria to survive in harsh conditions that would be lethal to vegetative cells
  • Dormant state of endospores
    • Allows bacteria to withstand extreme conditions without undergoing metabolic activity or replication.
191
Q

Describe the sporulation process

A
  1. DNA organised along cell axis
  2. The genome is replicated
    1. A genome copy is move to 1 pole and then enclosed in forespore septum
    2. Forespore produced by membrane invagination
  3. Cell membrane engulfs forespore in a second membrane
  4. Cortex between the 2 spore membranes accumulates calcium and dipicolinic acid
    1. Ca and the acid becomes dehydrated to <10% → no water = cell can’t overheat
    2. Becoming resistance to chemicals and heat
  5. Complex exosporium layers are produced
  6. Spore matures with complete cortical layers
  7. Release of spore
192
Q

Structural components of bacterial endospores

A
  • Exosporium (outermost layer)
    • Thin layer of proteins
    • Not essential for survival, maybe for dispersal
  • Spore coats (made up of spore-specific proteins)
    • Peptidoglycan cortex: removes water, contributing to the spore’s heat resistance
  • Core
    • Contains spore’s genome, cytoplasm n ribosomes
    • Metabolically inactive
    • Protected from denaturation thru dehydration
193
Q

What makes bacterial endospores highly resistant to environmental stresses?

A
  • Dehydration of the spore → prevents denaturation
  • Presence of small acid-soluble proteins → maintains the integrity of the spore’s genome by preventing the formation of pyrimidine dimers in DNA
  • Overall structure of endospore → protective barrier against detrimental factors
194
Q

What is the metabolic state of endospores?

A
  • Metabolically inactive structures
  • Inside the spore, no discernable metabolic activity
  • The core contains the genome, cytoplasm, and ribosomes, but they are in a dormant state.
195
Q

How does germination occur in bacterial endospores?

A
  • Germination is the process by which a dormant endospore returns to its vegetative state.
  • It starts with the uptake of water and amino acids, which act as triggers for germination.
    • This process is rapid, usually complete within 30 minutes.
  • As germination progresses, the spore loses its refractile (shiny) appearance due to rehydration and the loss of resistance.
  • The spore’s protective layers are broken down, and the core becomes metabolically active.
  • The released cell then begins to grow and divide in a normal manner.
196
Q

How does the cell wall composition change during germination?

A
  • After germination, cell produced from endospore is usually -
  • But peptidoglycan layer is rapidly built up
    • Results in +
  • Transition occurs as the vegetative cell regains its ability to synthesize peptidoglycan
197
Q

Virulence is determined by factors that aid in

A
  • Adhesion to n entry into cells
  • Antiphagocytic activity, immune system evasion
  • Production of toxins
198
Q

Conventional virulence factors

A
  • Bacterial toxins
  • Adhesins
  • LPS
  • Secreted hydrolytic enzymes
199
Q

Meningitis

A

Inflammation of the protective membranes that cover brain n spinal cord

200
Q

What causes meningitis?

A
  • Viruses
  • Bacteria
  • Fungi
  • Protozoa
201
Q

What does C.tetani do?

A

Over-activity of motor neurons causing muscle spasms

202
Q

Describe Tetanus toxin’s mechanism of action

A
  • Released by cell lysis, spreads through blood n lymph
    • Targets CNS
    • Binds to peripheral nerve terminals, transported along axons
  • Halts release of glycine and GABA neurotransmitters
    • They normally check nervous impulses
    • Absence of these checks result in muscular spasms
203
Q

Describe Haemophilus influenzae

A
  • Gram-negative coccobacillus
  • Non-encapsulated strains carried asymptomatically in urinrary tract
  • Cause of bacterial meningitis
204
Q

Hib vaccines

A

Vaccines that protect against Haemophilus influenzae type b (Hib) bacteria, a leading cause of severe bacterial infections in young children.

205
Q

Conjugated vaccines

A

Vaccines that use a peptide carrier to enhance the immune response to polysaccharide antigens, which are normally weakly immunogenic.

206
Q

PRP-T

A

One of the three conjugated Hib vaccines introduced in 1992. It uses a tetanus toxoid carrier

207
Q

PRP-OMP

A

One of the three conjugated Hib vaccines introduced in 1992. It uses a meningococcal outer membrane protein (OMP) carrier.

BS127: Agents of Infectious Disease (4 decks)

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