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module 102: T4 infection and immunity > intro to medical microbiology > Flashcards

intro to medical microbiology Flashcards

1
Q

How are bacteria named, use example of E.coli?

A
  • genus first, then species
  • underline or italics
  • Can abbreviate, so Escherichia coli becomes E. coli
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2
Q

Describe prokaryotes structure (bacteria)

A
  • no nucleus or membrane bound organelles
  • single, circular DNA (haploid)
  • 70S ribosomes (50S and 30S subunits)
  • peptidoglycan cell wall
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3
Q

Describe eukaryotes

A
  • membrane bound nucleus
  • chromosomes in nucleus (diploid)
  • 80S ribosomes (60S and 40S subunits)
  • no cell wall (except plants and fungi)
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4
Q

How are bacteria often classified?

A

by shape and staining

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5
Q

Describe how shape of bacteria is used to classify them

A
  • ROUND = coccus/cocci
  • LONG = bacillus/bacilli
  • a few are spiral/branched/comma shaped
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6
Q

What is the difference between gram positive and gram negative bacteria?

A

GRAM POSITIVE: no outer
membrane
GRAM NEGATIVE: outer membrane

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7
Q

What is the predominant stain used to classify bacteria and what are the results?

A
  • Gram stain
  • positive = purple
  • negative = pink
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8
Q

Describe Gram positive bacteria?

A
  • thick peptidoglycan layer
  • lipoteichoic and teichoic acid
  • inner cytoplasmic membrane
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9
Q

Describe Gram negative bacteria?

A
  • outer membrane made of lipopolysaccharide and has protein channels (porins)
  • thin peptidoglycan
  • inner cytoplasmic membrane
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10
Q

What are the synthetic pathways for peptidoglycan?

A
  • polymerisation of sugars
  • elongation of amino acid side-chains
  • transpeptidase
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11
Q

Why are the synthetic pathways of peptidoglycan important in medicine?

A

as all the steps are targeted by important classes of antibiotics

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12
Q

What does each synthetic pathway for peptidoglycan synthesis do?

A
  • POLYMERISATION OF SUGARS: to make the back-bone
  • ELONGATION OF AA SIDE CHAINS: to add the peptides
  • TRANSPEPTIDASE: to cross-link
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13
Q

Describe the peptidoglycan layer in bacteria?

A
  • SUGARS: glucosamine (NAG) and muramic acid (NAM)
  • amino acid peptides, resistant to enzymatic destruction
  • cross-linked by transpeptidase enzymes
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14
Q

Describe lipopolysaccharide in gram negative bacteria

A
  • lipid A = long-chain fatty acid anchor (active component)
  • core polysaccharide chain
  • variable CHO chain (= O antigen)
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15
Q

Why is lipopolysaccharide in gram negative bacteria important?

A
  • major structural component
  • effective permeability barrier (including to antimicrobials)
  • regulates host immune response
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16
Q

Which patterns of growth can be seen in bacteria?

A
  • MICROSCOPE: in clusters or chains
  • SOLIDE CULTURE MEDIUM: colonies are different sizes/shapes
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17
Q

How can bacterial growth be exploited to identify the pathogen?

A
  • patterns of growth
  • excrete enzymes, waste products
  • different requirements for growth (atmosphere ad nutrients)
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18
Q

What are the 3 possible bacterial atmospheric requirements?

A
  • aerobes
  • anaerobes (obligate anaerobes)
  • facultative anaerobes
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19
Q

Describe aerobe bacteria?

A

use oxygen as final electron acceptor (very efficient)

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20
Q

Describe anaerobe (obligate anaerobes) bacteria?

A
  • fermentation, final electron acceptor is organic molecule
  • okay when substrates are plentiful
  • oxygen usually toxic to them
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21
Q

Describe facultative anaerobe bacteria

A

can switch between aerobic and anaerobic metabolism

22
Q

What are some things bacteria can’t make themselves?

A
  • purine and pyrimidines
  • amino acid
  • vitamins
23
Q

What are the nutritional requirements for E. coli?

A
  • needs glucose and inorganic salts only
  • very easy to grow in lab
24
Q

What are the nutritional requirements for Treponema pallidum (syphilis)?

A
  • specialised enriched medium
  • hard to grow
25
Q

Describe capsules in bacteria

A
  • polysaccharide coat
  • ‘hides’ immunogenic cell wall
  • metabolic burden on the bacterium
  • grants virulence
  • immunity requires antibodies to the capsule
26
Q

Describe the ribosomes in bacteria

A
  • engines of protein synthesis
  • 70S (50S and 30S subunits)
  • each contains bacterial RNA and proteins
  • the RNA is the target of antibiotics and diagnostic tests
27
Q

Why do bacteria move?

A

chemotaxis (moving towards or away from chemical stimuli)

28
Q

How do bacteria move?

A
  • rotate a flagellum like a propeller
  • use a pilus like a grappling hook
  • corkscrew motility (spirochete)
29
Q

How do bacteria stick?

A

adhesin and receptor bind in a specific/complementary manner

30
Q

What is docking and anchoring in bacteria?

A
  • DOCKING: non-specific adherence
  • ANCHORING: specific adherance
31
Q

How do bacteria transfer genes?

A
  • transduction
  • conjugation
  • competence/transformation
32
Q

What are the mobile genetic elements of bacteria and what do they do?

A
  • plasmids
  • transposons
  • they code for toxins and antibiotic resistance genes
33
Q

Describe plasmids

A
  • circular ‘extra-chromosomal’ DNA
  • independently replicating
  • passed down to offspring
  • some transmitted between bacteria
34
Q

Describe transposons?

A
  • DNA sequences that are able to move location in the genome
  • encode transposase and other genes
35
Q

What are transposons mobile between?

A
  • genomic and plasmid DNA
  • plasmids
36
Q

State the 4 phases of bacterial growth

A
  • lag phase
  • exponential phase
  • stationary phase
  • death phase
37
Q

Describe the lag phase in bacterial growth

A
  • no increase in cell numbers
  • adjustment to new environment
  • gene regulation
38
Q

Describe the exponential phase in bacterial growth

A
  • cell doubling
  • slope of the curve = growth rate of organism in that environment
39
Q

Describe the stationary phase in bacterial growth

A
  • nutrients become depleted
  • metabolites build up
  • divison stops
  • gene regulation
40
Q

Describe the death phase in bacterial growth

A
  • exhaustion of resources
  • toxicity of environment
41
Q

In which phases of bacterial growth does gene regulation occur?

A

in the lag phase and stationary phase

42
Q

What are endotoxins?

A

lipopolysaccharides found in the cell wall of Gram-negative bacteria

43
Q

What are the steps to carrying out a gram stain?

A
  1. crystal violet
  2. iodine
  3. decolourisation with alcohol
  4. safranin counterstain
44
Q

What sugars are in the peptidoglycan?

A
  • glucosamine (NAG)
  • muramic acid (NAM)
45
Q

What is the other stain that can be used and in which context is it used?

A
  • Ziehl-Neelsen stain
  • for mycobacteria that have thick lipid membrane made of mycolic acids
46
Q

What are some bacterial growth requirements that are modified in the lab?

A
  • temperature
  • pH
  • salt content
47
Q

Give examples of bacteria that lack a cell wall and are not ‘free-living’

A
  • mycoplasma
  • chlamydia
48
Q

What are spores resistant to?

A
  • drying
  • temperature
  • disinfection
  • digestion
49
Q

Which medically important bacteria make spores?

A
  • bacillus spp
  • clostridium
50
Q

What is gene regulation important for in bacteria?

A
  1. conserve energy (prevent unnecessary gene expression)
  2. Adapt to environmental changes
  3. coordinated changes in expression of multiple genes

module 102: T4 infection and immunity (10 decks)

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