Bacteria Flashcards
What are the most common bacterial morphologies
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
Why is beneficial to bacteria to be small
Greater surface to volume ratio so they release more nutrients
Less time needed for division so they can pass on genetic traits rapidly
Where do odors come from
Bacterial metabolism
Degradation of apocrine secretion products
Leucine –> isovaleric acid
Propanoic acid
What is the gram stain
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
What are the 2 results from the gram stain
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
What are the capsules made of
Made of polysaccharides and AA
Covalently bound to the cell wall or outer membrane
What are exopolysaccharides
Form aggregates to protect from environment and form colonies
What are S layers
Facultative structures that non covalently bind to the cell surface
crystalline arrays; self assembly products
What are capsules
Confer resistance to host phagocytes/bacteriophages to keep environment hydrated
What are exopolysacchardises
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
What are the key components of a gram negative outer membrane
Phospholipids - carbohydrate
Porins and lipoproteins (covalently linked to peptidoglycan)
LPS (endotoxin) - potent activator of the immune system - low level of inflammation
What are peptidoglycans (murein)
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)
What is the composition of peptidoglycans
Glycan chains alternating N-acetylglucosamine (G) and N-acetylmuramic acid (M),
substituted via short peptides (L- and D-amino acids)
What are the key components of the cytoplasmic membrane
Phospholipids - Modulate membrane fluidity and permeability
Hopanoids - Modulate membrane fluidity and permeability
Proteins - transporter proteins
What are features of a chromosome
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
What are features of plasmids
Always dsDNA
variable copy number
Size between 2 kbp and 600 kbp
Can be self transferable
Carry resistance genes
What is the difference between eukaryotic and prokaryotic gene structure
Eukaryotes have introns
Prokaryotes have no introns (Open reading Frame)
Prokaryotes have smaller genes
What is an operon
an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter
How does transcription occur
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
What are the subunits of RNA polymerase
Alpha2, Beta, Beta’ and omega
How is transcription terminated (Rho-independent)
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
What is Rho - dependent termination
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
What are the differences between eukaryotic and prokaryotic transciption
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
What is the difference between eukaryotic and prokaryotic translation
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
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
What are Lithotropes and organotropes
Organo - organic - Heterotroph
Litho - inorganic - Autotroph
What is the criteria for bacterial growth
Temperature Nutrients pH Osmotic pressure Oxygen
What are the different classes of microorganims
Psychrophile
Mesophile
Thermophile
Extreme thermophile
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
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
How are bacteria in highly acidic conditions adapted
They use H+ as a metabolic tool
How are bacteria in highly alkaline conditions adapted
They use Na+ as a metabolic tool
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
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!)
What is an example of a NonHalophile, Halotolerant, Halophile and extreme halophile
E.Coli
Staphylococcus
Halobacterium salinarum
Archae
What nutrients do bacteria require
Nitrogen, sulfur, phosphorous, vitamins, K+, Ca2+, Mg2+ and trace elements (Fe, Cu, Zn…)
What are the toxic forms of oxygen Reactive oxygen species
Superoxide, Hydrogen peroxide, Hydroxyl radical
What enzymes detoxify ROS
Catalase
Superoxide dismutase and catalase - H2O2 into H2O
Superoxide reductase and catalse - O2- into H2O2 then H2O
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
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
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
What are the 4 phases of bacterial growth
Lag, Log, Stationary and death phase
Why do bacteria, which are O2 sensitive, need O2
Use of O2 as an electron acceptor
Production of enzymes which detoxify ROS
At high pH what is used to move the flagella
Ca2+
What does supercoiling DNA do
increases the stability of the genome of some thermophiles
Are reactive oxygen species always toxic?
All Reactive oxygen species are toxic
What is the by product of oxygen metabolism
. Reactive oxygen species are by-product from oxygen metabolism
What is more stable Ether or Ester linked phospholipids
Ether-linked phospholipids are more stable than ester-linked phospholipids
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
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
What are bacteriostatic chemical antimicrobial control
Bactericdal
Bacteriolytic
Keeps bacteria growth constant
Stops growth and triggers cell death
Destruction of bacterial cells
What are sterilant
Disinfectants
completely eliminate or destroy all forms of microorganism including spores
Kill microorganisms but not necessary endospores
What are antiseptics and germicides
Inhibit growth or kill microorganisms
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
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
How do Phenols work as antibacterial
local anesthetic at low concentration and antibacterial at high concentration
Disrupts the cytoplasmic membrane and denatures proteins
How do Alcohols work as antibacterial
Denature the proteins, lipid solvent, disrupting cytoplasmic membrane. Active concentration between 60-85%
How do aldehydes work as antibacterial
Alkylating agents containing aldehyde groups Formalin prevents bacterial growth. Modify proteins and DNA, causing cell death
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
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)
How do 2 - iodine releasing agents act as antibacterials
very powerful, but stain
Targets DNA and proteins
What are the 2 therapeutic strategies to treat bacteria
Antibiotics
Vaccination
Who came up with germ theroy
Louis Pasteur
What are Kochs postulates
Established the casual relationship between microbe and disease
- The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pureculture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
Who discovered penicillin
Alexander Fleming
What are 4 modes of antibiotic resistance
drug inactivation
target modification
efflux/impermeability
bypass
What are the types of antibiotics
Cell wall inhibitors
Protein Synthesis inhibitors
DNA metabolism inhibitors
What causes antibiotic resistance
Antibiotic misuse in human therapeutics Farming Agriculture Aquaculture Pets
What are the properties of an ideal antibiotic
Selective toxicity, inhibit an essential process
Stability and effectiveness
Low cost
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
How does B-lactams work
inhibit peptidoglycan cross-linking by irreversible inactivation D,D-transpeptidases
