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MICR2000 Microbiology > M1-Introduction to Microorganisms > Flashcards

M1-Introduction to Microorganisms Flashcards

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1
Q

What is microbiology?

A

Study of microscopic living organisms

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2
Q

What are the importance of microorganisms?

A
  • Oldest form of life
  • Largest mass of living material
  • Carry out major processes for biogeochemical cycles
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3
Q

What are the key structures of a bacterial cell?

A
  • Cytoplasmic membrane
  • Cytoplasm
  • Nucleus or nucleoid and ribosomes
  • Cell wall
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4
Q

What characteristics are in all bacterial cells?

A
  • Metabolism
  • Growth
  • Evolution
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5
Q

What characteristics are in some bacterial cells only?

A
  • Differentiation
  • Communication
  • Genetic exchange
  • Motility
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6
Q

What contributions did Robert Hooke make?

A
  • First description of microbes
  • Illustrated the fruiting structures of molds
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7
Q

What contributions did Antoni van Leeuwenhoek make?

A
  • First to describe bacteria
  • Observed in teeth scrapings, rain water and other specimens
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8
Q

What contributions did Louis Pasteur make?

A
  • Showed that microbes are responsible for fermentation
  • Demonstrated that bacteria which caused the spoilage of wine could be killed by heat that was not hot enough to evaporate the alcohol in wine
  • Disproved theory of spontaneous generation
  • Developed vaccines for anthrax, fowl cholera, and rabies
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9
Q

What contributions did Robert Koch make?

A
  • Definitely demonstrated the link between microbes and infectious diseases
  • Identified causative agents of anthrax and tuberculosis
  • Koch’s postulates
  • Developed techniques (solid media) for obtaining pure cultures of microbes
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10
Q

What are Koch’s postulates?

A
  • Bacteria must be present in every case of the disease
  • Bacteria must be isolated from the host with the disease and grown in pure culture
  • Specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
  • Bacteria must be recoverable from the experimentally infected host
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11
Q

What characteristics does cytoplasmic membrane have?

A
  • Phospholipid bilayer
  • Contains embedded proteins
  • Functions as a highly selective permeability barrier
  • Does not confer rigidity
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12
Q

What is the difference between bacterial and archaeal cytoplasmic membrane?

A
  • Bacterial membrane lipids contain fatty acids joined to glycerol via ester linkages
  • Archaeal membrane lipids contain repeating isoprene units joined to glycerol via ether linkages
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13
Q

What is the difference between gram-positive and gram-negative cell walls?

A
  • Structure of gram-positive cell walls: peptidoglycan + cytoplasmic membrane
  • Structure of gram-negative cell walls: outer membrane + peptidoglycan + cytoplasmic membrane
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14
Q

What is peptidoglycan?

A
  • Rigid structural layer that provides strength to the cell wall
  • Made of repeating polysaccharide unit (G+M)
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15
Q

What is the difference between the peptidoglycan in gram-positive and gram-negative cell walls?

A
  • Thinner and hidden in gram-negative cell walls
  • Thicker and exposed in gram-positive cell walls
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16
Q

What is the crosslinking of the repeating G+M unit of peptidoglycan in gram-positives?

A

-Occurs via formation of peptide interbridge

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17
Q

What is the crosslinking of the repeating G+M unit of peptidoglycan in gram-negatives?

A

-NH2 group of DAP of one glycan chain to COOH group of D-alanine on adjacent chain

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18
Q

How the repeating unit of G+M unit of peptidoglycan provides structural integrity?

A

-Crosslinking between peptidoglycan chains by peptide bonds, provides strength in X and Y directions

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19
Q

What does the gram-positive cell wall contain?

A
  • Up to 90% peptidoglycan
  • Teichoic acids embedded
  • Lipoteichoic acids: teichoic acids covalently bound to membrane lipids
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20
Q

What does the gram-negative cell wall contain?

A
  • Outer membrane: lipopolysaccharide (LPS), phospholipid
  • Periplasm: peptidoglycan
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21
Q

What does the outer membrane in gram-negative cell wall contain?

A

-lipopolysaccharide (LPS) layer: core polysaccharide, O-polysaccharide and lipid A (endotoxin)

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22
Q

What characteristics does gram-negative lipopolypeptide (LPS) have?

A
  • Comprises 50% of the mass of the outer membrane
  • Structural composition of LPS lipid A and core polysaccharide is generally conserved while the O-antigen varies
  • Highly toxic for humans
  • Toxic properties associated with LPS are mainly caused by endotoxin (lipid A)
  • Endotoxins cause fever and systemic toxic effects by stimulating the release of cytokines and other host inflammatory mediators from immune cells
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23
Q

What is periplasm in the gram-negative cell wall?

A
  • Space located between cytoplasmic and outer membranes
  • Have gel-like consistency
  • Houses many proteins
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24
Q

What is gram stain test?

A
  • Differentiate between gram-positive and gram-negative bacteria
  • Due to differences between cell walls of gram-positive and gram-negative bacteria
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25
Q

What is the procedure of gram stain test?

A
  1. Flood the heat-fixed smear with crystal violet for 1 min
  2. Add iodine solution for 1 min
  3. Decolourize with alcohol briefly
  4. Counterstain with safranin for 1-2 min
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26
Q

What are the results of the gram stain test?

A
  • Gram-positive: purple
  • Gram-negative: red/pink
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27
Q

What bacteria cannot gram stain?

A
  • Genus Mycobacterium
  • -*Acid fast bacteria: stained red using acid fast stain
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28
Q

What is S layer?

A
  • Most common cell wall type among Archaea
  • Consist of interlocking protein or glycoprotein arranged as a paracrystalline surface structure
  • Provides structural rigidity, barrier to diffusion of large molecules
  • Also found in some bacteria
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29
Q

What is the difference between archaeal cell walls and bacterial cell walls?

A

-Archaea do not contain peptidoglycan or an outer membrane in the cell wall

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30
Q

What is pseudomurein?

A

=Polysaccharide similar to peptidoglycan

  • Composed of N-acetylglucosamine and N-acetylalosaminuronic acid
  • Found in some methanogenic Archaea
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31
Q

What are capsules?

A

=Polysaccharide layers

  • Assist in attachment to surfaces (biofilm formation)
  • Aid in evasion of immune system
  • Resist desiccation
  • Occurs in both gram-positives and gram-negatives
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32
Q

Give an example of capsule and its function.

A

-Streptococcus pneumoniae: capsule allows the organism to avoid immune recognition

33
Q

What is fimbriae?

A

=Filamentous bacterial surface appendages

  • Involved in adherence
  • Primary function: adhesion
  • Some bacteria can produce more than one type of fimbriae
34
Q

What is flagella?

A

=Rotatable filamentous bacterial surface appendages

  • Involved in bacterial locomotion
  • Different arrangements: polar, lophotrichous or peritrichous
  • Helical in shape
  • Filament composed of the protein flagellin
  • Moves by rotation
35
Q

What is the structure of gram-negative flagellum?

A
  • Flagella filament is composed of many copies of a protein flagellin
  • Hook consists of a single type of protein and connects the filament to the motor at the base
  • Motor (Mot proteins) is anchored in the cytoplasmic membrane and cell wall, which drives the rotation of flagella
  • Fli proteins function as the motor switch, reversing the direction of rotation of the flagella in response to intracellular signals
36
Q

What is the process of flagella biosynthesis?

A

-Flagellin molecules are synthesized in cytoplasm and move up through a hollow core in the filament

37
Q

What is the movement made by polar flagellated cells?

A
  • Reversible flagella: rotation changed between clockwise and counter-clockwise
  • Unidirectional flagella: rotation unchanged; cell stops and reorients
38
Q

What is the movement made by peritrichous flagellated cells?

A

-Flagella pushed apart by tumbling to change direction

39
Q

What characteristics do archaeal flagella have?

A
  • Most archaea produce flagella
  • Capable of swimming motility
  • Structure of the archaeal flagella motor = not well known
  • Filament of archaeal flagella = often composed of several different flagellin proteins
  • Some archaeal flagellins = glycoproteins
  • Amino acid sequence of archaeal flagellins is not related to that of bacterial flagellins
40
Q

What is gliding motility?

A
  • Flagella-independent motility
  • Significant slower
  • Requires surface contact
41
Q

What is chemotaxis in peritrichous flagellated cells?

A
  • Bacteria respond to differences in chemical concentration
  • Attractants sensed by chemoreceptors
  • Increased tumbling as attractant concentration decreases
  • Decreased tumbling as attractant concentration increases
42
Q

How is chemotaxis measured?

A

-Capillary tube assay

43
Q

What is cell inclusion?

A
  • Many bacteria can synthesize carbon and energy storage compounds, like lipid or glycogen
  • Some bacteria can accumulate inorganic phosphage (PO43-) for nucleic acid, phospholipid and ATP synthesis
  • Other bacteria can oxidise H2S either to produce energy or as part of a CO2 fixation process
  • Magnetosomes: intracellular particles of magnetite (Fe3O4) that enable bacteria to orientate themselves in a specific arrangement within a magnetic field
44
Q

What are 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
45
Q

What are endospores?

A
  • Highly differentiated cells that is resistant to dessication, heat, harsh chemicals, and radiation
  • “Dormant” stage of bacterial life cycle
  • Ideal for dispersal via wind, water, or animal gut
  • Only present in some gram-positive bacteria
46
Q

What is the structure of endospore?

A
  • Differes markedly from that of the vegetative cell
  • Exosporium = outermost covering consisting of protein
  • Several spore coats may then be found
  • Cortex consists of a peptidoglycan layer
  • Core contains the core wall, cytoplasmic membrane, cytoplasm, DNA and ribosomes
47
Q

What is microbial growth?

A

=Increase in the number of cells within a population

  • Cells reproduce by binary fission
  • Cell numbers double every generation
48
Q

What is growth rate?

A

-Change in cell number or cell mass per unit time

49
Q

What is generation time/doubling time?

A

-Interval for the formation of two cells (from one cell)

50
Q

What is a batch culture?

A

-A closed-system microbial culture of fixed volume

51
Q

What is the typical growth curve for a bacterial population?

A
52
Q

What are the growth phases in batch culture?

A
  • Lag phase: period before growth begins at a maximal rate
  • Exponential phase: period of growth where the number of cells doubles during a constant time interval
  • Stationary phase: period of growth where there is no net increase in cell number
  • Death phase: period where cells begin to die
53
Q

What happens in 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
54
Q

What happens in exponential phase?

A
  • Increase in cell number is initially rather slow but increases at an ever faster rate
  • When cells are growing exponentially, the time taken for all components of the cell to double is the same (=balanced growth)
  • Growth is unrestricted as long as the concentration of all nutrients does not limit growth or toxic products do not build up
55
Q

What two parameters are in the maths of microbial growth?

A
  • Generation time (g): time required for the population to double in size
  • Mean growth rate constant (k): mean number of generations (divisions) per hour; =1/g
56
Q

What equation give the number of cells produced over a given incubation time?

A

N = N0 2n

57
Q

What equation give the number of generations required to produce N cells?

A

n = (log N - log N0) / log 2

58
Q

What equation give the generation time (g)?

A

g = t / n (hr)

-Since “n” generations happened over “t” incubation time

59
Q

What happens in stationary phase?

A
  • Occurs when 1 nutrient is limiting for growth or when inhibitory products accumulate
  • Some metabolic activity, other activities slow down
  • Bacteria adapt to stationary phase by activating the expression of specific genes
60
Q

What does the expression of genes involved in adaptation to stationary phase depend on?

A

A specific RNA polymerase sigma factor, RpoS

(sigma recognizes promoter and initiation site)

  • RpoS directs RNA polymerase to transcribe genes involved in stationary phase adaptation
  • RpoS binds to a distinct promoter consensus sequence
61
Q

Give an example of what happens in stationary phase.

A
  • In E. coli:
  • Stationary phase, cells smaller, increased resistance
  • Contain far more glycogen (carbon and energy storage)
62
Q

What happens in death phase?

A
  • Cell begins to die
  • May be associated with cell lysis
63
Q

What methods are used to measure growth?

A
  • Total cell count
  • Viable count
  • Turbidimetric measurements
64
Q

What is total cell count?

A

Direct counting of cells under a microscope

  • Advantage: Rapid way of estimating cell number
  • Disadvantages:
  • Dead cells not distinguished from living cells
  • Small cells difficult to see under microscope
  • Precision sometimes difficult to achieve
  • Phase contrast is required when sample is not stained

-Only suitable for bacteria at a density greater than 106 per ml

65
Q

What is viable count?

A
  • Has two different methods: spread plate method and pour plate method
  • Advantages:
  • Widely used in food, medical, dairy and aquatic microbiology
  • Highly sensitive
  • Samples containing few cells can be counted
  • Use of selective media allows counting of specific organisms in mixed populations

-Disadvanges:

  • Number of colonies that develop may depend on conditions
  • Small colonies may be overlooked during counting
  • To avoid errors, replicate plates of key dilutions are required
  • Cell clumping may reduce counts
66
Q

What is spread plate method and its assumption?

A

Assumption: each viable cell produces a single colony

67
Q

What is pour plate method and its assumption?

A
  • Assumption: each viable cell produces a single colony
  • Bacteria must be able to withstand 45oC for a limited time when they are placed in molten agar
68
Q

What is the procedure for viable counting?

A
  • Serial dilutions
  • Cultures usually need to be diluted otherwise the number of colonies developing become too great and makes it impossible to count
69
Q

What is turbidimetric method?

A
  • Rapid method that uses a spectrophotometer
  • Measures light that is not scattered by the bacteria, optical density (OD)
  • Accurate measure of cell number
  • At high cell densities, backscattering leads to a deviation from linearity
  • Without disturbing or destroying a culture
70
Q

What are the properties of a useful industrial microbe?

A
  • Produces spores or can be easily inoculated
  • Grows rapidly on a large scale in inexpensive medium
  • Produces desired product quickly
  • Should not be pathogenic
  • Amenable to genetic manipulation
71
Q

What are primary metabolites?

A

-Produced during exponential growth

72
Q

What are secondary metabolites?

A
  • Produced during stationary phase
  • Not essential for growth
  • Often significantly over-produced
73
Q

What is a biofilm?

A

A structured community of bacterial cells enclosed in a self-produced matrix and adhered to an inert or living surface

74
Q

What is the development of biofilm?

A
75
Q

Why do bacteria form biofilms?

A
  • Biofilms are a means of microbial self defense
  • Biofilm formation allows cells to colonize favorable niches
  • Biofilms enable bacteria to live together
  • Biofilm formation is a survival strategy
76
Q

What are the importances of biofilms in medicine?

A
  • Bacteria that form biofilms cause persistent (chronic) infections
  • Bacteria can withstand the action of the host defense system and the highest deliverable doses of antibiotics
77
Q

How do biofilms become so resistant to antimicrobials?

A
  • Slow penetration: outer layers absorb damage
  • Stress response: inner layers have more time to adapt
  • Altered microenvironment: nutrient depletion creates zones of altered activity

Persister cells: cells tolerant to antibiotics due to state of dormancy

-Antimicrobial depletion: adsorption of antibiotics, lack of penetration

78
Q

What is green fluorescent protein (GFP) and its function?

A
  • Has multiple colours
  • Tagging of cells
  • Direct monitoring of live cells
  • No need to stain

MICR2000 Microbiology (6 decks)

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