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University - Microbiology > Bacteria > Flashcards

Bacteria Flashcards

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1
Q

What are the most common bacterial morphologies

A

Cocci - round shape, diplococci is pairs of round cells
Streptococci is a chain of round cells

Rods - elongated, pilli like cells

Curved - curved shape elongate cells - generated by cytoskeleton proteins which creates the curve

Spiral - cell shape adapted to organism lifestyle which helps the bacteria penetrate the mucus of
epithelial cells

Exotic - Star shaped or rectangular

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2
Q

Why is beneficial to bacteria to be small

A

Greater surface to volume ratio so they release more nutrients

Less time needed for division so they can pass on genetic traits rapidly

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3
Q

Where do odors come from

A

Bacterial metabolism

Degradation of apocrine secretion products

Leucine –> isovaleric acid

Propanoic acid

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4
Q

What is the gram stain

A

Crystal violet stain - penetrate skin and stay attached

Iodine used to fix - forms large complexes

Alcohol used to wash

Safranin used as a counter stain

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5
Q

What are the 2 results from the gram stain

A

Violet cells - crystal violet trapped in cell envelope

Pink cells - crystal violet washed away and the pink counterstain has taken over - gram negative - cell wall isnt thick so stain can be washed away

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6
Q

What are the capsules made of

A

Made of polysaccharides and AA

Covalently bound to the cell wall or outer membrane

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7
Q

What are exopolysaccharides

A

Form aggregates to protect from environment and form colonies

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8
Q

What are S layers

A

Facultative structures that non covalently bind to the cell surface
crystalline arrays; self assembly products

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9
Q

What are capsules

A

Confer resistance to host phagocytes/bacteriophages to keep environment hydrated

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10
Q

What are exopolysacchardises

A

Homo or hetero polysaccharides

Non covalently attached to the cell surface

Important for biofilm formation

Some are economically important

Form aggregates to protect from environment and form colonies

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11
Q

What are the key components of a gram negative outer membrane

A

Phospholipids - carbohydrate

Porins and lipoproteins (covalently linked to peptidoglycan)

LPS (endotoxin) - potent activator of the immune system - low level of inflammation

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12
Q

What are peptidoglycans (murein)

A

Protects cell from environment by forming a rigid envelope surrounding the cytoplasmic membrane of most bacteria

Made of 2 sugars - one binds glucans the other starts the transpeptidase reaction

Scaffold for the display of polymers and proteins

Exoskeleton (resistance to osmotic stress)

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13
Q

What is the composition of peptidoglycans

A

Glycan chains alternating N-acetylglucosamine (G) and N-acetylmuramic acid (M),
substituted via short peptides (L- and D-amino acids)

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14
Q

What are the key components of the cytoplasmic membrane

A

Phospholipids - Modulate membrane fluidity and permeability

Hopanoids - Modulate membrane fluidity and permeability

Proteins - transporter proteins

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15
Q

What are features of a chromosome

A

Always made of dsDNA

Circular chromosome in the vast majority of bacteria

Vary in size between 0.5 - 14.8 Mbp

Organised as a nucleoid

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16
Q

What are features of plasmids

A

Always dsDNA

variable copy number

Size between 2 kbp and 600 kbp

Can be self transferable

Carry resistance genes

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17
Q

What is the difference between eukaryotic and prokaryotic gene structure

A

Eukaryotes have introns

Prokaryotes have no introns (Open reading Frame)

Prokaryotes have smaller genes

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18
Q

What is an operon

A

an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter

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19
Q

How does transcription occur

A

RNA polymerase scans DNA forming a loose complex

The sigma factor binds to a specific sequence upstream at the start codon (closed complex) (-35 and -10 region)

DNA is then undwinded allowing the formation of an open complex

Transcription starts and the sigma factor is released

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20
Q

What are the subunits of RNA polymerase

A

Alpha2, Beta, Beta’ and omega

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21
Q

How is transcription terminated (Rho-independent)

A

Requires a palindromic GC-rich region upstream of an AT-rich sequence

Once the GC rich region has been transcribed it forms a hairpin structure that makes RNA polymerase fall apart

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22
Q

What is Rho - dependent termination

A

Rho proteins recognise and bind to 72 residues which are G-C rich

RNA dependent ATPase activity of the Rho protein causes the RNA downstream to wrap around itself, Rho unwinds the RNA-DNA duplex when it reaches the polymerase, releases the RNA polymerase

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23
Q

What are the differences between eukaryotic and prokaryotic transciption

A

Transcription site in eukaryotes is nucleus whereas cytoplasm in prokaryotes

1RNA pol in prokaryotes whereas 3 in eukaryotes

Eukaryotes, termination involves AAUAAA seq (mRNA cleavage)

mRNA is modified in eukaryotes via splicing

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24
Q

What is the difference between eukaryotic and prokaryotic translation

A

80s ribosomes bind mRNA efficiently in the absence of tRNA (eukaryotes)
70s interact with mRNA more productively in the presence of tRNA (prokaryotes)

The 40S subunit is guided by the 5’ cap on mRNA (eukaryotes)
The 30S subunit recognises the Shine-Dalgarno sequence (prokaryotes)

Transcription and translation are coupled in prokaryotes

Eukaryotic translation is specifically inhibited by cycloheximide

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25
Q

What are the 2 metabolism pathways

A

Phototropic - uses sunlight for energy

Chemotropic - uses chemicals for energy

Organisms can flip between the 2 depending on available resource

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26
Q

What are Lithotropes and organotropes

A

Organo - organic - Heterotroph

Litho - inorganic - Autotroph

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27
Q

What is the criteria for bacterial growth

A 
Temperature
Nutrients 
pH 
Osmotic pressure 
Oxygen
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28
Q

What are the different classes of microorganims

A

Psychrophile

Mesophile

Thermophile

Extreme thermophile

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29
Q

How are psychrophiles adapted to cold temperatures

A

Increased membrane fluidity - higher content of unsaturated polyunsaturated and methyl-branched fatty acids, shorter acyl-chain length

Production of Anti-freeze proteins - Bind to small ice crystals to inhibit their growth

Production of cryoprotectants - Trehalose and exopolysaccharides

Production of cold adapted enzymes - higher proportion of a helices, less weak bonds and interdomain interactions increases flexability

30
Q

How are thermophiles adapted to high temperatures

A

Genome protection - stabilisation of DNA by DNA-binding proteins - introduction of supercoils - Resistance to denaturation favored by high G%-C%

Modification of membrane compostistion - Ether-linked phospholipids, Single lipid layer

Production of thermostable proteins

Existence of thermostable chaperonins

31
Q

How are bacteria in highly acidic conditions adapted

A

They use H+ as a metabolic tool

32
Q

How are bacteria in highly alkaline conditions adapted

A

They use Na+ as a metabolic tool

33
Q

What is a NonHalophile, Halotolerant, Halophile and extreme halophile`

A

NonHalophile - Cant live in NaCl environments
Halotolerant - can live in concentrated NaCl environments
Halophile - Can live in high NaCl environments
Extreme Halophile - can live in extremely high NaCl environments

34
Q

How do bacteria adaptic to osmotic pressures

A

Response to osmotic stress
Regulation of water movements by passive diffusion and aquaporins
Production of compatible solutes (betaine, proline, glutamic acid…)
Release of solutes by mechano-sensitive channels

Salt requirement in Halophiles
Stabilization of the S-layer glyco-protein by Na+ ions
Accumulation of K+ as a compatible solute (>4M in the cell!)

35
Q

What is an example of a NonHalophile, Halotolerant, Halophile and extreme halophile

A

E.Coli

Staphylococcus

Halobacterium salinarum

Archae

36
Q

What nutrients do bacteria require

A

Nitrogen, sulfur, phosphorous, vitamins, K+, Ca2+, Mg2+ and trace elements (Fe, Cu, Zn…)

37
Q

What are the toxic forms of oxygen Reactive oxygen species

A

Superoxide, Hydrogen peroxide, Hydroxyl radical

38
Q

What enzymes detoxify ROS

A

Catalase

Superoxide dismutase and catalase - H2O2 into H2O

Superoxide reductase and catalse - O2- into H2O2 then H2O

39
Q

What is an example obligate, Facultative ,micro aerobes

What is an example of anaerobes aerotolerant and obligae anaerobes

A

Pseudomonas aeruginosa, Escherichia coli, Campylobacter jejuni, Streptococcus mutans and Clostridium difficile

40
Q

How do you measure bacterial growth

A

Direct measurement - Flow cytometry, Microscopic counts and viable counting (dilutions)

Indirect measurement - Optical density, Dry weight and metabolic activity

Bacterial growth curve

41
Q

What are the limitations of optical density measurement

A
  • requires high cell densities (>107 cells/ml)
    • does not distinguish live vs dead cells
    • OD values differ depending on organisms
    • does not work with molds and filamentous bacteria
42
Q

What are the 4 phases of bacterial growth

A

Lag, Log, Stationary and death phase

43
Q

Why do bacteria, which are O2 sensitive, need O2

A

Use of O2 as an electron acceptor

Production of enzymes which detoxify ROS

44
Q

At high pH what is used to move the flagella

A

Ca2+

45
Q

What does supercoiling DNA do

A

increases the stability of the genome of some thermophiles

46
Q

Are reactive oxygen species always toxic?

A

All Reactive oxygen species are toxic

47
Q

What is the by product of oxygen metabolism

A

. Reactive oxygen species are by-product from oxygen metabolism

48
Q

What is more stable Ether or Ester linked phospholipids

A

Ether-linked phospholipids are more stable than ester-linked phospholipids

49
Q

What are the 3 physical methods of antimicrobial control

A

Heat - thermal death point and death time, Boiling water, Dry oven, pasteruization

Irradiation methods - Ionizing radiation - Xrays, Gamma, electron - food industry - E = hc/wavelength, Nonionizing radiation

Filtrations - USed to sterilize gases or liquids that can be damaged by heat - Can be any porosity

50
Q

What is the temperature and time needed for the pasterurization methods HTST and UHt

A

HTST - 72C for 15 seconds

UHT - 140C for 2-5 seconds

51
Q

What are bacteriostatic chemical antimicrobial control

Bactericdal

Bacteriolytic

A

Keeps bacteria growth constant

Stops growth and triggers cell death

Destruction of bacterial cells

52
Q

What are sterilant

Disinfectants

A

completely eliminate or destroy all forms of microorganism including spores

Kill microorganisms but not necessary endospores

53
Q

What are antiseptics and germicides

A

Inhibit growth or kill microorganisms

54
Q

How do you measure antimicrobial activity

A

Etest - strip, spread on cells on agar and place strip - measure inhibition zone, higher concentration antibiotics at the top and less at the bottom

Disc diffusion - Place discs with different antibiotics to measure how effective each antibiotic is against the bacteria

MIC - Minimum inhibitory concentration MIC is the lowest concentration of a drug inhibiting the visible growth of a test organism after overnight incubation. MIC is about inhibition

MBC - is the lowest concentration of a drug that kills over 99.9% of a test organism after overnight incubation. MBC is about killing the bacteria

55
Q

What are chemicals used for antimicrobial control

A

Phenolic compounds

Alcohols

Aldehydes

Quaternary ammonium compounds (quat)

1 – chlorine-releasing agents

2 – iodine-releasing agents (iodine/iodophors) – very powerful, but stain Target DNA and proteins

56
Q

How do Phenols work as antibacterial

A

local anesthetic at low concentration and antibacterial at high concentration
Disrupts the cytoplasmic membrane and denatures proteins

57
Q

How do Alcohols work as antibacterial

A

Denature the proteins, lipid solvent, disrupting cytoplasmic membrane. Active concentration between 60-85%

58
Q

How do aldehydes work as antibacterial

A

Alkylating agents containing aldehyde groups Formalin prevents bacterial growth. Modify proteins and DNA, causing cell death

59
Q

How do Quaternary ammonium compounds work as antibacterial

A

Interact with phospholipids of the cytoplasmic membrane Cationic detergents Long chains with charged tail allows for interaction to disrupt membrane

60
Q

How does 1-chlorine releasing agents act as antibacterial

A

sodium hypochlorite (bleach) ionises to produce Na+ and the hypochlorite ion OCl-, in equilibrium with hypochlorous acid (HOCl)

61
Q

How do 2 - iodine releasing agents act as antibacterials

A

very powerful, but stain

Targets DNA and proteins

62
Q

What are the 2 therapeutic strategies to treat bacteria

A

Antibiotics

Vaccination

63
Q

Who came up with germ theroy

A

Louis Pasteur

64
Q

What are Kochs postulates

A

Established the casual relationship between microbe and disease

  1. The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.
  2. The microorganism must be isolated from a diseased organism and grown in pureculture.
  3. The cultured microorganism should cause disease when introduced into a healthy organism.
  4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
65
Q

Who discovered penicillin

A

Alexander Fleming

66
Q

What are 4 modes of antibiotic resistance

A

drug inactivation
target modification
efflux/impermeability
bypass

67
Q

What are the types of antibiotics

A

Cell wall inhibitors

Protein Synthesis inhibitors

DNA metabolism inhibitors

68
Q

What causes antibiotic resistance

A 
Antibiotic misuse in human therapeutics
Farming
Agriculture
Aquaculture
Pets
69
Q

What are the properties of an ideal antibiotic

A

Selective toxicity, inhibit an essential process

Stability and effectiveness

Low cost

70
Q

How do bacteria become resistant to B-lactams

A

Inactivation by B-lactamases - Beta lactamases can hydrolyse antibiotic, causing it to be inactive as it structure no longer resembles D-Ala-D-Ala structure

mutation of the target enzyme - usually gram positive bacteria

secretion of the antibiotic - Gram negative

modification of the synthetic pathway targeted by B-lactams

71
Q

How does B-lactams work

A

inhibit peptidoglycan cross-linking by irreversible inactivation D,D-transpeptidases

University - Microbiology (8 decks)

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