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MICR2000 > Introduction > Flashcards

Introduction Flashcards

1
Q

Robert Hooke

A

First description microbes

Fruiting structure of moulds

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2
Q

Antoni van Leeuwenhoek

A

First description bacteria

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3
Q

Louis Pasteur

A 
Bacteria --> fermentation
Food sterilising
Disprove spontaneous generation
Develop methods to control growth
Vaccines
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4
Q

Robert Koch

A

Microbes –> infectious diseases
Koch’s postulates
Develop techniques to culture microbes

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5
Q

Koch’s Postulates

A
  1. X needs to be present in every case of Y
  2. X must be grown in pure culture
  3. Cells from a pure culture of X must cause disease in a healthy animal
  4. X must be reisolated and shown to be the same as the original
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6
Q

All bacterial cells

A

Metabolism
Evolution
Growth

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7
Q

Some bacterial cells

A

Differentiation
Communication
Genetic exchange
Motility

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8
Q

Bacterial cytoplasmic membrane

A

fatty acids joined to glycerol via ester linkages

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9
Q

Archaeal cytoplasmic membrane

A

isoprene units joined to glycerol via ether linkages

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10
Q

Peptidoglycan

A

peptide bonds (amino acids) and glycosidic bonds (sugars):

  • N-acetylglucosamine (G)
  • N-acetylmuramic acid (M)
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11
Q

Gram + Cell Wall

A 
-90% peptidoglycan
Teichoic acids
Lipoteichoic acids
-Peptidoglycan = outer layer
-Crosslinking through formation of peptide interbridge
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12
Q

Gram - Peptidoglycan crosslinking

A
  • 10% peptidoglycan
  • Sandwiched
  • OM has LPS layer
  • LPS: core polysaccharide. O-polysaccharide, lipid A (endotoxin)
  • [LPS] = patient outcome
  • Crosslinking through NH2 group of DAP of one glycan chain to COOH group of D-alanine on adjacent chain
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13
Q

Capsules

A 
Polysaccharide
Attachment (biofilm)
Evasion of immune system
Looks wet
\+ and -
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14
Q

Periplasm

A
  • Space between cytoplasmic and OM
  • Gel-like
  • Contain proteins
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15
Q

Gram stain

A
  • Crystal violet + peptidoglycan (+) –> purple
  • Crystal violet + less peptidoglycan (-) –> clear
  • Clear (-) + counterstain –> pink
\+ = purple
- = pink
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16
Q

Archaea cell walls

A 
S layer
Interlocking proteins and glycoproteins
No OM or peptidoglycan
Some have pseudomurein
- N-acetylglucosamine (G)
- N-acetyltalosaminuronic acid (M)
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17
Q

Fimbriae

A

Filamentous, linear projections
Adhesion
Multiple types
Some with adhesive domains along shaft that anchor cell by ‘zippering effect’

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18
Q

Bacterial Flagella

A
  • Rotatable filamentous bacterial surface appendages involved in bacterial locomotion
  • Different arrangements:
    • Peritrichous (Starfish)
    • Polar (Sperm)
    • Lophotrichous (Jellyfish)
  • Helical in shape, composed of flagellin
  • Hook: single type of protein, connects filament to motor at base
  • Motor (Mot proteins): anchored in the membrane and cell wall, drives rotation of flagella
  • Fli proteins: motor switch, reversing direction of rotation in response to IC signals
  • Around 50 genes: structural, chaperone, regulatory proteins
  • Flagellin molecules synthesised in cytoplasm, move up through hollow core in filament
  • 20,000 flagellin –> one filament
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19
Q

Archaeal Flagella

A

Most
Several different flagellin proteins
Amino acid sequence of archaeal flagellins is not related to bacterial flagellins

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20
Q

Gliding motility

A

Flagella-independent
Surface contact, slower

  1. Excretion of polysaccharide slime (cyanobacteria)
  2. Type IV pili, twitching motility by repeated extension and retraction (Myxococcus xanthus)
  3. Gliding-specific membrane proteins (Flavebacterium johnsoniae)
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21
Q

Cell motion as a behavioural response

Chemotaxis
Phototaxis
Aerotaxis
Osmotaxis
Hydrotaxis
A
  • Taxis: directed movement in response to gradients
  • Chemotaxis: chemicals
  • Phototaxis: light
  • Aerotaxis: oxygen
  • Osmotaxis: osmolarity
  • Hydrotaxis: water
22
Q

Run and tumble

A

Chemoreceptors –> chemical concentration

More attractant –> more directed –> less tumbling, more running

23
Q

Phosphate

A
  • Some can accumulate inorganic phosphate PO43- for nucleic acid, phospholipid, ATP synthesis
  • Accumulated in P-rich environments, used in limiting environments
24
Q

Sulphur

A
  • Some can oxidise H2S to produce energy in fixation of CO2

- Elemental sulphur S stored in sulphur globules in the periplasm

25
Q

Magnetosomes

A
  • Intracellular particles of magnetite (Fe3O4)
  • Enable bacteria to orient themselves in a specific arrangement within a magnetic field
  • Magnetosomes in aquatic bacteria –> orientation in water column
26
Q

Gas Vesicles

A
  • Confer buoyancy in planktonic cells
  • Spindle-shaped gas-filled structures made of protein
  • Gas vesicle membrane impermeable to water
  • Allows photosynthetic Bacteria to optimise position in water column
27
Q

Endospores

A
  • Highly differentiated cells that is resistant to harsh conditions/environments
  • “Dormant” stage of bacterial life cycle
  • Ideal for dispersal via wind, water or animal gut (like a seed)
  • Only present in some gram-positive bacteria
28
Q

Microbial growth

A

Increase in number of cells

29
Q

Binary fission

A

Cell elongation
Septum formation
Cell separation

30
Q

Growth rate
Generation time
Batch culture
Growth curve

A 
Growth rate- change in cell number/mass per unit time
Generation time (doubling time)- interval for formation of two cells
Batch culture- closed-system microbial culture of fixed volume
Growth curve- growth as a function of time
31
Q

Growth phases in batch culture

A

Lag
Exponential
Stationary
Death

32
Q

Lag phase

A
  • Cells adapted to stationary phase transferred to fresh medium
  • Cells transferred from rich to minimal medium
  • In both cases induction of new enzymes is required
33
Q

Exponential Phase

A
  • Number of cells doubles during a constant time interval
  • Increase initially slow but increases at an ever faster rate
  • Time taken for all components of the cell to double is the same (balanced growth)
  • Growth is unrestricted (excess nutrients, no toxic products)
34
Q

Stationary Phase

A
  • 1 limiting nutrient or accumulation of inhibitory products
  • Some metabolic activity slow down
  • E. coli cells get smaller and contain more glycogen
  • Adapt by activation expression of certain genes
    • RNA polymerase composed of core enzyme and sigma factor (holoenzyme)
    • Holoenzyme recognises promoter and initiates transcription
    • After initiation of transcription, sigma factor dissociates
    • RpoD is major sigma factor in bacteria
    • RpoD directs transcription of most genes in the cell
    • RpoD is active in exponential and stationary phase
    • RpoS directs RNA polymerase to transcribe genes involved in stationary phase adaptation
    • RpoS binds to distinct promoter consensus sequence
    • Majority of transcription still depends on RpoD
35
Q

Death phase

A

-Cells begin to die (cell lysis)

36
Q

Total cell count

A
  • Direct counting of cells under microscope in a chamber of known volume
  • Rapid estimate of cell number
  • Can’t distinguish live and dead cells
  • Difficult to see under microscope
  • Precision difficult to achieve
  • Phase contrast required when not stained
  • Suitable for density greater than 106 per ml (accuracy)
37
Q

Viable Count

A
  • Spread plate method
  • Assumption that each viable cell with produce a single colony
  • 10-fold dilutions to make sure a suitable number is plated
  • Number of colonies may depend on conditions
  • Small colonies could be overlooked
  • Replicate plates (accuracy)
  • Cell clumping could reduce counts
  • Highly sensitive
38
Q

Turbidimetric Measurements

A
  • Spectrophotometer
  • Measures light not scattered by bacteria
  • Calibration of OD vs viable cell count
  • High cell density –> backscattering –> deviation from linearity
  • Rapid measurements without disturbing culture
39
Q

Primary Metabolite

A

-Produced during exponential growth (alcohol)

40
Q

Secondary Metabolite

A
  • Produced during stationary phase (antibiotics)
  • Not essential for growth
  • Often significantly over-produced
41
Q

Penicillin Production

A
  • Stationary phase
  • Excreted into media
  • Extracted using organic solvents
42
Q

Sterilisation
Inhibition
Decontamination
Disinfection

A

Sterilisation- killing or removal of all viable organisms within a growth medium
Inhibition- effectively limiting microbial growth
Decontamination- treatment of abject to make it safe to handle
Disinfection- directly targets removal of all pathogens, not necessarily all microbes

43
Q

Heat Sterilization

Decimal reduction time
Thermal death time
Autoclave
Pasteurisation

A
  • Most widely used
  • High temperatures –> denature macromolecules
  • Endospores can survive heat
  • Decimal reduction time- time required for 10-fold reduction in viability
  • Thermal death time- time it takes to kill all cells at a given temperature
  • Autoclave- sealed heating device that uses steam under pressure (moist heat sterilization)
    • 121 degrees, 10-15 minutes
  • Pasteurisation- precisely controlled heat to reduce the microbial load in heat-sensitive liquids
    • Doesn’t kill all organisms (not sterilisation)
    • Controls pathogens and spoilage organisms
    • Milk: 71 degrees for 15 seconds
    • UHT milk: 135 degrees for 1-2 seconds
44
Q

Radiation Sterilization

A

Microwaves, UV, gamma rays, electrons
UV has sufficient energy to cause modifications and breaks in DNA
-decontamination of surfaces
- Cannot penetrate solid surfaces (limited to exposed surfaces)
-Ionising radiation
- Electromagnetic radiation of sufficient energy to produce ions and other relative molecular species
Electrons, hydroxyl radicals, hydride radicals
- Cathode ray tubes, X-rays, radioactive nuclides
- Used in medical and food industry
- Approved by WHO and is used in USA for decontamination of foods

45
Q

Filter Sterilization

A

-Avoids use of heat for sensitive liquids and gases
- Pores of filter are too small for organisms to pass through
- Large enough to allow liquid or gas to pass through
-Depth filters
- High efficiency particulate air (HEPA) filters
-Membrane filters
Function more like a sieve

46
Q

Chemical Growth Control

A

-Bacteriostatic, bacteriocidal and bacteriolytic
-MIC
- Synthetic agents (growth factor analogues)
- Sulfanilamide (inhibits production of folic acid)
- Isoniazid (interferes with synthesis of myolic acid, a mycobacterial cell wall component)
- Antibiotics (including semi-synthetic agents)
Microbially produced

47
Q

Antibiotics

A
  • Targets properties not present in humans
  • Cell wall synthesis
  • Protein synthesis (50S and 30S inhibitors)
48
Q

B-lactam Antibiotics

A
  • Penicillin G active mainly against Gram +
  • Chemically modified semi-synthetic antibiotics to change properties
  • Transpeptidase enzymes in cell wall bind to penicillin (PBP)
  • When PBP bind to penicillin, cross linking does not occur
  • Cell wall synthesis continues –> weakened cell wall
  • Penicillin-PBP complex stimulates release of autolysins (enzymes that degrade the cell wall) –> degraded cell wall
49
Q

Antimicrobial Resistance Mechanisms

A

-Lacks structure that the antibiotic inhibits
Mycoplasmas lack a cell wall –> resistant to penicillin
-Impermeable to antibiotic
Most G- bacteria impermeable to penicillin
-Can inactivate antibiotic
B-lactamases cleave B-lactam ring (plasmids)
-Modify target of antibiotic
Mutations in PBPs, ribosomes
-Develop resistant biochemical pathway
Folic acid taken up from environment instead of being synthesised
-Efflux
Tetracycline efflux pathway

50
Q

Staphylococcus aureus

A

Vancomycin is an antibiotic against S. aureus

  • Glycopeptide antibiotic –> binds to D-Ala D-Ala on pentapeptide to block cross linking
  • Also targets cell wall –> more difficult to develop resistance

Can develop resistance
-Replaces D-Ala D-Ala with D-Ala D-Lac
Peptidase cleaves D-Ala from D-Ala D-Ala and ligase adds lactate
-D-Ala D-Lac is still recognised for cross linking

MICR2000 (6 decks)

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