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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
What are the 2 metabolism pathways
Phototropic - uses sunlight for energy Chemotropic - uses chemicals for energy Organisms can flip between the 2 depending on available resource
26
What are Lithotropes and organotropes
Organo - organic - Heterotroph Litho - inorganic - Autotroph
27
What is the criteria for bacterial growth
``` Temperature Nutrients pH Osmotic pressure Oxygen ```
28
What are the different classes of microorganims
Psychrophile Mesophile Thermophile Extreme thermophile
29
How are psychrophiles adapted to cold temperatures
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
How are thermophiles adapted to high temperatures
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
How are bacteria in highly acidic conditions adapted
They use H+ as a metabolic tool
32
How are bacteria in highly alkaline conditions adapted
They use Na+ as a metabolic tool
33
What is a NonHalophile, Halotolerant, Halophile and extreme halophile`
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
How do bacteria adaptic to osmotic pressures
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
What is an example of a NonHalophile, Halotolerant, Halophile and extreme halophile
E.Coli Staphylococcus Halobacterium salinarum Archae
36
What nutrients do bacteria require
Nitrogen, sulfur, phosphorous, vitamins, K+, Ca2+, Mg2+ and trace elements (Fe, Cu, Zn…)
37
What are the toxic forms of oxygen Reactive oxygen species
Superoxide, Hydrogen peroxide, Hydroxyl radical
38
What enzymes detoxify ROS
Catalase Superoxide dismutase and catalase - H2O2 into H2O Superoxide reductase and catalse - O2- into H2O2 then H2O
39
What is an example obligate, Facultative ,micro aerobes What is an example of anaerobes aerotolerant and obligae anaerobes
Pseudomonas aeruginosa, Escherichia coli, Campylobacter jejuni, Streptococcus mutans and Clostridium difficile
40
How do you measure bacterial growth
Direct measurement - Flow cytometry, Microscopic counts and viable counting (dilutions) Indirect measurement - Optical density, Dry weight and metabolic activity Bacterial growth curve
41
What are the limitations of optical density measurement
- 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
What are the 4 phases of bacterial growth
Lag, Log, Stationary and death phase
43
Why do bacteria, which are O2 sensitive, need O2
Use of O2 as an electron acceptor Production of enzymes which detoxify ROS
44
At high pH what is used to move the flagella
Ca2+
45
What does supercoiling DNA do
increases the stability of the genome of some thermophiles
46
Are reactive oxygen species always toxic?
All Reactive oxygen species are toxic
47
What is the by product of oxygen metabolism
. Reactive oxygen species are by-product from oxygen metabolism
48
What is more stable Ether or Ester linked phospholipids
Ether-linked phospholipids are more stable than ester-linked phospholipids
49
What are the 3 physical methods of antimicrobial control
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
What is the temperature and time needed for the pasterurization methods HTST and UHt
HTST - 72C for 15 seconds | UHT - 140C for 2-5 seconds
51
What are bacteriostatic chemical antimicrobial control Bactericdal Bacteriolytic
Keeps bacteria growth constant Stops growth and triggers cell death Destruction of bacterial cells
52
What are sterilant | Disinfectants
completely eliminate or destroy all forms of microorganism including spores Kill microorganisms but not necessary endospores
53
What are antiseptics and germicides
Inhibit growth or kill microorganisms
54
How do you measure antimicrobial activity
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
What are chemicals used for antimicrobial control
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
How do Phenols work as antibacterial
local anesthetic at low concentration and antibacterial at high concentration Disrupts the cytoplasmic membrane and denatures proteins
57
How do Alcohols work as antibacterial
Denature the proteins, lipid solvent, disrupting cytoplasmic membrane. Active concentration between 60-85%
58
How do aldehydes work as antibacterial
Alkylating agents containing aldehyde groups Formalin prevents bacterial growth. Modify proteins and DNA, causing cell death
59
How do Quaternary ammonium compounds work as antibacterial
Interact with phospholipids of the cytoplasmic membrane Cationic detergents Long chains with charged tail allows for interaction to disrupt membrane
60
How does 1-chlorine releasing agents act as antibacterial
sodium hypochlorite (bleach) ionises to produce Na+ and the hypochlorite ion OCl-, in equilibrium with hypochlorous acid (HOCl)
61
How do 2 - iodine releasing agents act as antibacterials
very powerful, but stain | Targets DNA and proteins
62
What are the 2 therapeutic strategies to treat bacteria
Antibiotics | Vaccination
63
Who came up with germ theroy
Louis Pasteur
64
What are Kochs postulates
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 pure culture. 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
Who discovered penicillin
Alexander Fleming
66
What are 4 modes of antibiotic resistance
drug inactivation target modification efflux/impermeability bypass
67
What are the types of antibiotics
Cell wall inhibitors Protein Synthesis inhibitors DNA metabolism inhibitors
68
What causes antibiotic resistance
``` Antibiotic misuse in human therapeutics Farming Agriculture Aquaculture Pets ```
69
What are the properties of an ideal antibiotic
Selective toxicity, inhibit an essential process Stability and effectiveness Low cost
70
How do bacteria become resistant to B-lactams
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
How does B-lactams work
inhibit peptidoglycan cross-linking by irreversible inactivation D,D-transpeptidases

University - Microbiology (8 decks)

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