Microbiology Flashcards
What is the major cause of infectious disease in humans?
Bacteria
What do bacteria do?
Encounter and gain access to host
Evade defence mechanisms
Colonise and maintain colony
Result in host toxicity or damage
Potential for spread of infection (but not always the case)
What are the key features of a Prokaryote cell?
Smaller and simpler in size than eukaryotic cells
No membrane-bound organelles (no nucleus, mitochondria, Golgi etc.)
Single DNA genome
Plasmid DNA free in cytoplasm
Enzymes and ribosomes free in cytoplasm
Rigid, complex wall with appendages
Extreme adaptation to environment (pH, enzymes, viscosity etc.)
What is Flagella, Fimbriae and pili used for?
Flagella used for motility and also as a sensory organelle (detect chemicals in the environment, the temperature of the environment etc).
Fimbriae and pili used for cell adhesion
Sex pili important for movement of DNA between cells by conjugation
What do capsules do?
Surrounds certain Gram –ve and Gram +ve bacteria
Aids cells adherence by the slime layer
Protect from neutrophils (impermeable to lysosome contents)
Purpose of cell wall?
To give structure to the cell
To maintain positive internal osmotic pressure
What does Peptidoglycan contain?
Contains N-acetylglucosamine (NAG) and N-acetylmuramic (NAM)
Difference in structure between Gram -ve and Gram +ve
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What is Peptidoglycan?
A substance forming the cell walls of many bacteria
Explain Gram +ve Peptidoglycan?
Contains a Carbohydrate backbone at the top – just NAM and NAG connected together
Contains an amino acid cross bridge – five glycine
Contains amino acid side chain – different amino acids
Explain Gram -ve Peptidoglycan?
Has the same structure as +ve but no amino acid cross bridge
Explain Gram +ve cell wall?
You have a phospholipid bilayer (cytoplasmic membrane) and protein channels going through.
Then you have the peptidoglycan layer, consisting of NAM and NAG residues, peptide bonds. Then you have cell wall (surface) proteins attached; and you have teichoic acid and lipoteichoic acid.
Explain Gram -ve cell wall?
You have the cytoplasmic membrane.
The peptidoglycan is very thin and this is called periplasm.
The entire cell wall consist of the peptidoglycan layer and an outer membrane. On the outer membrane you have LPS – O polysaccharide.
Where are Periplasm found?
Only found in Gram -ve cell walls.
What is contained in the aqueous gel-like region between the two membranes of Gram –ve bacteria?
Contains enzymes associated with nutrient acquisition and transport
Also contains defence enzymes used to resist antibiotics
Which cell wall has an outside membrane?
Gram -ve cell walls.
What is on the outside cell wall of Gram -ve?
- Porins that allow passive diffusion of molecules into periplasmic space
- Braun’s lipoprotein that anchors outer membrane
- Llipopolysaccharides
Explain how both Grams are differentiated?
Explain the test carried out?
- Heat with crystal violet
- Add iodine solution
- Decolourise with alcohol
- Stain with safranin
They both take in dye:
- Insoluble crystals are formed
- Crystals escape Gram –ve
- Red stain seen in Gram –ve
What are the three types of active transport in bacteria?
PMF-driven transport
ABC transport (ATP-Binding Cassette)
Group translocation eg. Glucose 6-P
Explain the structure of Nucleoid in Prokaryotic DNA?
Circular, supercoiled, double stranded
Not associated with histone proteins
Generally only one chromosome
Explain the structure of Plasmids in Prokaryotic DNA? And functions?
(not essential for survival)
Small loops of extrachromosomal DNA
May contain genes that are expressed in response to certain situations
May be used to transfer genes between cells
Cell be incorporated into the chromosome
Single DNA stand transferred between cells by conjugation using ‘rolling circle’ replication
Explain Ribosome and Translation?
There are:
Small 30S subunit binds in mRNA – bind to the messenger RNA
Large 50S subunit binds, completes 70S ribosome
– binds to and completes the 70s ribosome
Explain Streptococcus Pneumoniae ?
Gram +ve
Encapsulated coccus
Causes respiratory infections
SEM x3750
Explain Escherichia Coli?
Gram –ve
Flagella and fimbriae
Enteric, urinary and nosocomial infections
SEM x3515
Explain Escherichia Coli 0157:H7 – anaerobic form of E.Coli?
Gram –ve rods
Anaerobic
Causal agent of haemorragic disease due to toxic secretion
SEM x9335
Explain Clostridium difficile?
Gram +ve rods
Anaerobic
Forms part of normal gut microflora
Causes inflammation (colitis) and abdominal disease
SEM x1200
Explain Helicobacter Pyori?
Gram –ve spirals
Moves using flagella
Associated with chronic superficial gastritis
SEM x2200
Explain Mycobacterium tuberculosis?
Gram +ve rods
Moves using flagella
Able to reside inside tissue due to hydrophobic cell wall
SEM x3000
Explain Staphylococcus aureus?
Gram +ve cocci
MRSA
Causes a variety of infections and disease
SEM x13335
Explain how Antibacterial Chemotherapy works?
Treats a bacterial disease and causes minimal toxicity to host.
It does this by exploiting biochemical differences between the infectious organism and the host organism .
What are the two types of antibiotics?
Bactericidal and bacteriostatic
Bactericidal = kills bacteria
Bacteriostatic = stops bacteria growing (it can also kill bacteria in patients, it’s just a matter of time and exposure)
What is Minimum Bactericidal Concentration (MBC)?
The lowest concentration of antibacterial agent, that reduces the viability of a bacterial inoculum by more or equal to 99.9%
What is Minimum Inhibitory Concentration (MIC)?
The lowest concentration of a chemical, which prevents visible growth of a bacterium.
When is a drug considered bactericidal?
A drug is considered bactericidal if:
MBC is no more than four times the MIC.
Explain the Antibiotic Susceptibility Test to determine MIC?
Strips impregnated with a gradient of antibiotic, are placed on a lawn of bacteria and are incubated.
MIC is determined at the point where the zone of inhibition intersects the scale.
What are the Two strategies for Antibacterial Chemotherapy?
Targeting reactions and Targeting structures.
Explain class 1 reaction for Anabolic cell metabolism?
Carbon sources used to produce simple compounds
Similar mechanism in prokaryotes and eukaryotes
Bacteria can utilise alternative carbon sources
Explain class II reaction for Anabolic cell metabolism?
Use Class I products to make small molecules
Different pathways exist in prokaryotes and eukaryotes
Sam pathway may have differing sensitivity
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