Bacteria Flashcards
(95 cards)
1
Q
what are the different bacterial morphologies?
A
- cocci
- rods
- curved
- spiral
- exotic - star-shaped cells
2
Q
what is the cocci morphology of bacteria?
A
- simplest, round-shaped cells
- cell machinery at septum for elongation
- some form pairs = diplococci
- some form chains = streptococci
- division planes can be parallel or perpendicular
- form complex organisations like tetrads, sarcinae (multiple perpendicular divisions
- can form microcolonies (piles of cells)
3
Q
what is the rod morphology of bacteria?
A
- elongated cells
- bacilli = 1 rod
- diplobacilli = 2 rods
- multiple chains of rods = streptobacilli
4
Q
what is the name given to a bacteria with a mixture of round cocci and rods?
A
coccobacilli
5
Q
what is the curved morphology of bacteria?
A
- governed by cytoskeleton proteins to create curved shape
- asymmetrical growth is maintained
6
Q
what is the spiral morphology of bacteria?
A
spirillum:
- cell shape adapted to organism lifestyle
- helps bacteria move as a corkscrew and penetrate into mucus of epithelial cells
7
Q
how can bacterial morphologies change during the cell cycle?
A
- in aquatic environment it forms swarmer cells - has flagella so can swim
- during life cycle, forms a stalk appendage so bacteria can adhere to surfaces
- as stalk grows, they divide asymmetricaly
- produce mobile form (swim) and immobile form (adhere)
8
Q
what is the advantage of bacteria being small?
A
large SA:V ratio
- increases nutrient exchange and growth rate
- higher intracellular nutrient concentration
- rapid evolution due to high selection rate of mutations and faster divisions
9
Q
why do bacteria appear to be different colours?
A
- they themselves aren’t coloured
- they produce pigments as colonies
- pigments fulfil roles in bacterial life cycles
- Prodigiosin = immunosuppressant
- staphyloaxanthin and violacein = antioxidant, detoxify ROS
- pyocyanin = cytotoxicity, neutrophil apoptosis, proinflammatory
10
Q
why do bacteria have odours?
A
- they form biproducts from metabolism which aren’t necessity for life, but do produce odour
- contribution to human odours via degragation of aprocrine products
- conversion of leucine to isovaleric acid by Staph
- production of propanoic acid by propionibacteria - decarboxylation of amino acids to form polyamines
- putrescine, spermidine, cadaverine have role is ROS and signalling
11
Q
what is the gram staining process?
A
- colony sample spread onto glass slide and stained with crystal violet, which is +ve charge and penetrates cell envelope
- iodine solution, -ve charge, penetrates cell envelope, and allows crystal violet to form large complexes
- crystal violet is either stuck in envelope or washed off
- counter stain safranin is applied and stains cells that had crystal violet washed off
12
Q
what is gram positive in the gram stain?
A
- These bacteria retain methyl violet in their thick peptidoglycan cell walls
- contain no outer membrane
- Examples of Gram-positive bacteria are
Staphylococcus and Streptococcus
13
Q
what is gram negative in the gram stain?
A
- These bacteria have only thin peptidoglycan cell walls
- contain an outer membrane
-Gram negative bacteria therefore appear pink-red. - Examples of Gram-negative
bacteria are Escherichia, Pseudomonas and Neisseria
14
Q
what bacteria does the gram stain not work on?
A
Mycobacteria
- has a unique cell envelope composition where the lipids interfere with the staining process
15
Q
what are S-layers?
A
- found in gram +ve and -ve
- non-covalently bound to cell surface- - facultative (don’t exist in most model organisms)
- proteinaceous crystalline arrays - self assembly products
- 20% of bacterial production
- not all bacteria have them
- function unknown
16
Q
what are capsules?
A
- found in gram +ve and -ve
- made of polysaccharide
- some made of amino acids (poly-gamma-D-glutamate)
- covalently bound to peptidoglycan (gram +ve) or outer membrane (gram -ve)
- resistannt to phagocytes and bacteriophages
- keep environment hydrated
17
Q
what are exopolysaccharides?
A
- homo- or heteropolysaccharides
- non-covalently bound to cell surface
- important for biofilm formation
- form aggregates to protect fom environment
- enables formation of colonies
- economic importance: xanthan gum
18
Q
what are the key components of the outer membrane in gram negative bacteria?
A
- phospholipid bilayer
- innerface = phospholipids
- outerface = lipopolysaccharide, contains hydrophobic region
- variable-O-antigen polysaccharide determines antigen on cell surface
- contains porins for solute transport
- lipoproteins are covalently linked to peptidoglycan
- LPS endotoxin is a potent activator of the immune system: can trigger inflammation
19
Q
what is peptidoglycan?
A
- made of murein
- maintains cell shape and forms exoskeleton
- acts as scaffold to display proteins
- protective role
- acts as a sieve to regulate dynamic exchanges with environment
- elastic 3D network
- present in almost all bacteria
- resistant to osmotic stress
20
Q
what is the composition of peptidoglycan?
A
- made of murein
- glycan chains alternating N-acetylglucosamine G and N-acetylmuramic acid
- substituted via short peptides (L and D amino acids)
21
Q
how is peptidoglycan assembled?
A
- transpeptidation reaction with enzymes which are covalently bound to the stem
22
Q
what are the key components of the cytoplasmic membrane?
A
- phospholipid bilayer
- unsaturated fatty acids modulate membrane fluidity and permeability due to kinks in hydrocarbon chain
- amphipathic molecules for compartmentalisation
- hopanoids modulate membrane fluidity and permeability
- protein transporters make membrane selectively permeable for specific polar molecules
23
Q
what is the bacterial chromosome made up of?
A
- dsDNA
- singular, circular chromosome
- 0.5-14.8mbp
- organised as a nucleoid: histone-like proteins enable supercoiling
24
Q
what is the bacterial plasmid made up of?
A
- dsDNA
- variable copy number
- 2-600kbp
- self-transferable by horizontal transfer
- conjugation: physical contact between bacteria to transfer plasmid DNA
- carry resistance genes
25
what is the gene structure of bacteria?
- no introns
- continuous coding sequence via open reading frame (ORF)
- operons: one promoter, several ORFs
- genes are smaller than eukaryotic genes
26
how is gene transcription initiated?
1. RNAP scans DNA forming a loose complex
2. sigma factor binds to shine-dalgarno sequence upstream of start codon (-35 and -10)
3. DNA is unwound to form an open complex
4. transcription begins and sigma factor is released
27
what is rho-independent transcription termination?
1. requires palindromic GC-rich region upstream of an AT-rich sequence
2. once the GC-rich region has been transcribed, it forms a hairpin
3. hairpin causes dissociation of RNAP, helped by the AT-rich sequence (few H-bonds)
28
what is rho-dependent transcription termination?
1. rho proteins recognise and bind to 72 GC-rich residues
2. RNA-dependent ATPase wraps the downstream RNA around itself
3. once it reaches the polymerase, rho unwinds the RNA-DNA heteroduplex and releases RNAP
29
how is the genetic machinery different between prokaryotes and eukaryotes?
- transcription site is cytoplasm for bacteria (nucleus for eukaryotes)
- 1 RNAP in bacteria, 3 RNAP eukaryotes
- termination involves palindromic GC-rich region (eukaryotes require AAUAAA)
- mRNA is modified in eukaryotes, but not in bacteria
30
how large are the ribosomes in bacteria compared to eukaryotes?
70S in bacteria
- 50S + 30S
80S in eukaryotes
- 60S + 40S
31
what are the differences in translation between bacteria and eukaryotes?
- bacterial 70S ribosomes interact with mRNA productively in presence of tRNA
- 30S subunit recognises SD sequence
- transcription and translation are coupled in bacteria
- eukaryotic 80s ribosomes bind mRNA efficiently in absence of tRNA
- 40S subunit is guided by 5' cap on mRNA
- compartmentalised in eukarytoes
- translation inhibited by cycloheximide
32
what does bacterial growth require?
- temperature
- pH
- osmotic pressure
- nutrients
- oxygen
33
what are the cardinal temperatures for bacteria?
Minimum: below this, no growth ca occur as the membranes gel and transport processes are too slow to maintain metabolism
Optimum: an increased enzymatic activity so that reactions occur at the maximal possible rate
Maximum: after this point, proteins become denatured, cytoplasm collapses and cell lysis occurs, causing metabolic reactions to halt
34
name 4 bacteria and their optimal temperatures:
1. P. vacuolata = 4C
- psychrophile
2. E. coli = 37C
- mesophile
3. T. aquaticus = 70C
- thermophile
4. P. fumarii = 106C
- extreme thermophile
35
how are psychrophiles adapted to cold temperatures?
1. increased membrane fluidity
- more unsaturated and polyunsaturated methyl-branched fatty acids
- limit membrane cohesion
2. production of anti-freeze proteins
- AFPs bind to ice crystals to inhibit their growth by covering water-accessible surfaces of ice
3. production of cryoprotectants
- trehalose and exopolysaccharides lowers freezing temp of water to preserve fluids
4. production of cold-adapted enzymes
- more a-helices and less weak bonds to combat low enthalpy
36
how are thermophiles adapted to high temperatures?
1. genome protection
- by DNA-binding proteins stabilise DNA
- reverse DNA genes form supercoils - harder to pull apart
- high GC% - difficult to denature
2. modify membrane composition
- stable ether-linked phosolipids
- single lipid layer: glycerol tetraethers
3. thermostable proteins
- more ionic and hydrophobic interactions to form stronger bonds
4. thermostable chaperonins
- maintain protein folding
- thermosome in Pyrodictium abyssi
37
how are acidophile metabolisms adapted to their environment?
- increased membrane impermeability
- use protons as currency
- ATP depends on oxidative phosphorylation and needs H+ for this
- use H+ to import/export Na+
- H+ powers motility: when pumped in, H+ triggers conformational change to move flagella
- H+ secretion systems via antiporters
- DNA/protein repar mechanisms
- reverse membrane potential and increased osmolarity (K+ ions)
38
how are alkaliphile metabolisms adapted to their environment?
- Na+ as currency
- use Na+ to make ATP
- used for motility, imports/exports etc
- high affinity transporters for Na+
39
how are bacteria adapted to osmotic stress?
- regulate water movements by passive diffusion and aquaporins
- produce compatible solutes like proline, glutamic acid and betaine
- release solutes via mechano-sensitive channels
- halophiles accumulate osmolites in their cytoplasm
40
what are halophiles?
- require high salt conc to grow
| - S-layer is stabilised by Na+ ions, and K+ must be >4M in the cell
41
what are non-halophiles?
cannot be exposed to high salt conc
42
what are halotolerant bacteria?
can deal with high osmotic pressure by high salt conc, but to an extent
43
what are extreme halophiles?
- usually archaea
| - need high salt conc
44
what nutrients do bacteria require?
- nitrogen
- sulphur
- phosphorus
- vitamins
- K+, Ca2+, Mg2+ (cofactors)
- trace elements (Fe, Cu, Zn)
45
what nutrients do bacteria require?
- nitrogen
- sulphur
- phosphorus
- vitamins
- K+, Ca2+, Mg2+ (cofactors)
- trace elements (Fe, Cu, Zn)
46
what do bacterial metabolisms need?
- energy source
- source of electrons
- carbon source
bacteria can switch from one metabolism to another depending on the available resources
47
what are the toxic forms of Reactive Oxygen Species (ROS)?
1. superoxide
2. hydrogen peroxide
3. hydroxyl radical (most toxic)
48
what is the detoxification reaction in ROS?
02 + 4e- + 4H+ = H20
49
what enzymes do bacteria produce to detoxify ROS?
- catalase/peroxidase: convert H2O2 to H20
- superoxide dismutase + catalase converts O2 to H2O2 then H2O
- superoxide reductase + catalase coverts O2 to H2O2 then H2O
50
what are the different oxygen requirements for different bacteria?
1. obligate aerobes: catalase + superoxide dismutase
- use exclusively O2 for respiration
- P. aeruginosa
2. facultative aerobes: catalase + superoxide dismutase
- can use O2 for respiration
- E. coli
3. microaerophiles
- require O2 for respiration
- C. jejuni
4. anaerobes aerotolerant: superoxide dismutase
- do not use O2 for respiration
- S. mutans
5. obligate anaerobes = C. difficile
51
what are the 3 direct measurements of bacterial growth?
1. Microscopic counts
2. flow cytometry
3. viable counting
52
what are microscopic counts for bacterial growth?
- manually count no. bacteria per unit on glass slide
ads: cheap
disads: time-consuming, must be accurate
53
what is flow cytometry?
- machine pumps cell suspension through capillary
- suspension is hit by a laser and measures scattered light by the bacteria present
ads: can distinguish live/dead bacteria, distinguish specific species using antibodies, high sensitivity
disads: expensive equipment
54
what is viable counting?
- serial dilutions of inoculum is spread on agar
- colonies are counted using cell counters
ads: distinguishes different species, identifies live bacteria
disads: time consuming, assumes one colony comes from one cell
55
what are the 3 indirect measurements of bacterial growth?
1. optical density
2. dry weight
3. metabolic diversity
56
what is optical density?
Optical density
- expose cell suspension to light through prism with given wavelength
- measure unscattered light, which is proportional to no. cells in suspension
disads: requires high cell densities, doesn't distinguish live/dead cells, OD values vary depending on organisms, doesn't work with molds/filamentous bacteria
57
what is the dry weight measurement of bacterial growth?
- measures cell weight after freeze-drying
| disads: time-consuming, requires expensive equipment
58
what is the metabolic activity measurement of bacterial growth?
- measure production of specific metabolites
ads: can measure activity of a specific group of bacteria
disads: complicated to do
59
what is the bacterial growth curve?
- exponential growth of bacteria
| - new generation every 20-30 mins
60
what are the 4 phases of the bacterial growth curve?
1. lag phase
- metabolism starts, but no division
2. log phase
- exponential increase in population
- logarithmic growth due to binary fission
3. stationary phase
- microbial deaths balance production of new cells
- fermentation releases acidic compounds which lower pH of the medium, so can no longer sustain growth
4. death phase: decrease in population
61
what is the thermal death point?
- min temp at which all organisms are killed in 10 mins in a particular liquid
62
what is the thermal death time?
- min time required to kill all bacteria in a particular liquid at a give temperature
63
what are the 3 methods microbes can be killed using heat?
1. moist heat (boiling/autoclave): 15 mins at 121C under pressure to kill spores
2. dry heat (oven): direct flaming, incineration >150C for 2 hrs
3. pasteurisation (mild heat)
- HTST: 72C for 15secs, kills 99.9% viable microorganisms in milk
- UHT: 140C, 2-5secs
64
how can irradiation kill microbes?
- UV, x-rays and gamma rays have short enough wavelengths to kill bacteria
- the shorter the wavelength, the more energy provided (indirect proportional)
ionising radiations:
- food industry, medical/lab equip
- DNA destruction via ROS and breaking double strand
non-ionising radiation:
- surface decontamination
- DNA damage
65
how can filtration kill microbes?
- sterilise gases or liquids that can be damaged by heat
- porosity of filters (1mm to 0.01um) can be chosen for specific microbes
1. nucleopore filter: membrane with holes that filters microbes
2. membrane filter: mesh of continuous polymers
3. depth filters: fibres stuck on top of one another
66
what are bacteriostatic antimicrobial agents?
- doesn't kill bacteria, only stops growth
- maintain no. cells
- maintain viable cell count
67
what are bactericidal antimicrobial agents?
- stop growth
| - trigger cell death as viable cell count decreases
68
what are bacteriolytic antimicrobial agents?
- cause cell lysis
69
what are sterilants?
- eliminate all forms of microorganisms, including spores, on objects
- e.g. ethylene oxide: gas so is effective
- most powerful antimicrobial compound we can use
70
what are disinfectants?
- kill microorganisms, but not endospores, on objects
| - e.g. alcohol (60-85% in water)
71
what are antiseptics and germicides?
- inhibit growth
- kill microorganisms on tissues
- e.g. handwash
72
how can antimicrobial activity be measured?
1. disc diffusion technique
2. Minimum Inhibitory Concentration (MIC): growth inhibition measurement
3. Minimum Bactericidal Concentration (MBC): cell death measurement
73
what is the disc diffusion technique to measure antimicrobial activity?
1. inoculate plate with a liquid culture sample
2. discs containing antimicrobial agents are placed on surface
3. incubate for 24-48hrs
4. test organism shows susceptibility to some agents, indicated by zones of inhibition
74
what is the MIC growth inhibition measurement of antimicrobial activity?
- MIC is the lowest concentration of a drug inhibiting the visible growth of a test organism after overnight incubation
75
what is the MBC cell death measurement of antimicrobial activity?
- MBC is the lowest conc of a drug killing 99.99% of a test organism after overnight incubation
- test no. viable cells after being in contact wit antimicrobial agent
76
what are phenolic compounds?
- aromatic derivatives
- low anaesthetic at low conc, antibacterial at high conc
- disrupts cytoplasmic membrane and denatures proteins
77
how are alcohols used in antimicrobial control?
- denatures proteins and disrupts cytoplasmic membranes
- lipid solvent
- active conc between 60-85%
78
how are aldehydes used in antimicrobial control?
- alkylating agents containing aldehyde groups
- formalin prevents bacterial growth
- modify proteins and DNA, leading to cell death
79
what are quaternary ammonium compounds?
- interact with phospholipids of the cytoplasmic membrane
- cationic detergents
- long chains with charge tail allows disruption of membrane
80
what are halogen-releasing agents?
1. chlorine-releasing agents
- bleach ionises to form Na+ and hypochlorite ion OCl-, in equilibrium with hypochlorous acid (HOCl)
- form chlorinated bases in DNA and oxidation of proteins
2. iodine-releasing agents
- iodine/iodophores
- target DNA and proteins
81
what are the two major therapeutic strategies against pandemics?
1. antibiotics
| 2. vaccinations
82
who described germ theory?
Louis Pasteur 1860
83
what is Koch's Postulates?
- in 1890s, Koch discovered the causal relationship between a microbe and a disease
- used germ theory
1. microbe must be found in all organisms suffering the disease, but not in healthy organisms
2. microbe can be isolated from diseased organism and grown in culture
3. cultured microbe should cause disease when applied to healthy organism
4. microbe is reisolated from the inoculated host and identified as being identical to the original microbe
84
who discovered penicillin?
Alexander Fleming in 1928, produced by a fungus mold
85
what are the major classes of antibiotics?
1. Cell wall inhibitors
- beta-lactams
- glycopeptides
2. protein synthesis inhibitors
- aminoglycosides
- cyclines
- MLS
- oxazolidinones
3. DNA metabolism inhibitors
- quinolones
86
what causes antibiotic resistance?
- antibiotic overuse and misuse in human therapeutics
- farming: animals can be fed with antibiotics at subtherapeutic doses (4x human consumption)
- agriculture: treatment of diseases in plants
- aquaculture
- pets
87
what are the key properties of an ideal antibiotic?
1. It must display selective toxicity towards the target bacteria
- must inhibit an essential process or inhibit virulence
2. it must be stable in the host and active at low concentration
3. It must be cheap
88
what are beta-lactams?
- penicillin antibiotic that inhibits peptidoglycan polymerisation
- they target D, D-transpeptidase penicillin binding proteins (PBP) in bacteria
- they form covalent bonds with amino acid in position 4, to form a crosslink from C-terminal to acceptor group
- they are structural analogs of D-Ala-D-Ala C-terminal residues in peptide stem
- they are used by PBP as substrates and inactivate these enzymes irreversibly
89
what are the 4 models of antibiotic resistance by bacteria?
1. drug inactivation: beta-lactamases
2. target modification: low affinity
PBPs/overexpression
3. efflux/impermeability: efflux systems in gram -ve bacteria
4. bypass: alternative pathway
90
what are the 4 methods in which are bacteria resistant to beta-lactams?
1. inactivation by beta-lactamases
2. mutation of the target enzyme PBP
3. secretion of the antibiotic by gram negative bacteria
4. modification of the synthetic pathway targeted by beta-lactams
91
how do bacteria inhibit beta-lactams via beta-lactamases?
beta-lactamases can hydrolyse the antibiotic, causing it to become inactive as the structure no longer resembles D-Ala-D-Ala:
1. nucleophilic attack by catalytic serine
2. covalent complex penicillin-beta-lactamase
3. penicillin hydrolysis
beta-lactamases evolved from the same family as PBPs
92
how does mutation in the target enzyme PBP make bacteria resistant to beta-lactams?
- used by gram-positive bacteria
Two methods:
1. They form low affinity PBPs so that there reduced affinity of beta-lactams for PBP
2. Overexpress PBP targetted by beta-lactams
93
how does mutation in the target enzyme PBP make bacteria resistant to beta-lactams?
- used by gram-positive bacteria
Two methods:
1. They form low affinity PBPs so that there reduced affinity of beta-lactams for PBP
2. Overexpress PBP targetted by beta-lactams
94
how do gram negative bacteria secrete the beta-lactam in antibiotic resistance?
e. g. P. aeruginosa
1. overproduction of the MexAB-OprM system
- carbapenem resistance
2. Overproduction of the MexEF-OprN system
- imipenem resistance
95
how do bacteria modify the synthetic pathway that is targeted by beta-lactams in antibiotic resistance?
- they remodel how peptidoglycan is synthesised
- L, D transpeptidases cause different type of crosslinking which is beta-lactam insensitive
- they form a 3,3 bond rather than a 3,4 bond
