Intro lecture Pathogenesis Flashcards
(25 cards)
Describe the main characteristic and size of these types of infectious agents
1) Prions
2) Viruses
3) Bacteria
4) Fungi
5) Parasites
1) Infectious protein, unknown
2) DNA or RNA + protein coat, 20-800nm
3) Prokaryotic cell, 0.2 - 30um
4) Eukaryotic, plant like. Yeasts are single celled, 1-15um. Moulds are filamentous, 1-15um
5) Eukaryotic, animal. Protozoa are single celled, 2-30um. Metazoa are tissue differentiation, 3mm - 5m.
Name 6 different factors in disease emergence
1) Microbial adaptation to new environment/host
- High genome mutation rate (Esp RNA viruses)
2) Ecologicalchanges
- Agricultural practices and water ecosystems
3) Population growth
4) Human demographics and behaviour
- Sexual behaviour
- IV Drug use
- Air travel
5) Technology and industry
- organ and tissue transplantation
6) Breakdown in public health measures
- Inadequate or reduced preventative programs
- inadequate vector control programs
Main differences between Animal and bacterial cell
Bacterial cell has cell wall and nuceloid. Doesnt have golgi or mitochondria.
Bacterial cell is smaller than eurkaryotic.
Hasnt got an ER or nucelus or membrane bound organelles
Chromosome is a single DNA circle.
Ribosomes are 70S with no membrane
Replication via binary fission.
Name the 5 key components of bacteria
Cytoplasmic membrane, cytoplasmic matrix, ribosomes, genome (made of chromosomes and/or plasmids), cell wall
What are functions of the plasma cytoplasmic membrane
Contains protein and lipid.
Essential for survival.
Allows selective interaction with environment: entry of nutrient and elimination of waste, while maintaining internal organisation.
Location of many metabolic processes, eg respiration
What does the cytoplasmic matrix contain
Mostly water
Relatively hypertonic
Packed with ribosomes
Often contains inclusion bodies
Purpose of ribosomes in bacteria
Many ribosomes for protein synthesis. Made of protein and RNA
Compare prokaryotic and eukaryotic ribosomes
rRNA of prokaryotic cells contains fewer bases than euks, also fewer proteins than euks. Overall the subunit sizes are smaller so a prokaryotic cell has 50S and 30S which combines to give 70S whereas the Eukaryotic cell has 60S and 40S which combines to give 80S
Describe the nucleoid
No nuclear membrane
Contains mainly DNA (Also RNA and protein)
Bacterial chromosome is single closed circle of dsDNA, looped and super coiled
What are plasmids
Circular dsDNA, supercoiled
Replicate independently of chromosome
Variable size and copy number
Describe and mention the functions of the cell wall
Rigid layer outside the plasma membrane.
Gives cell shape and protects against osmotic lysis/toxic substances.
Shape and strength due to peptidoglycan layer.
Site of action of some antibiotics
What is the basics of gram staining?
Method used to differentiate bacterial species into two large groups - gram positive and gram negative.
Differentiates it by detecting the chemical and physical differences in their cell walls by detecting peptidoglycan.
Gram positive bacteria retains the crystal violet dye.
Gram negative bacteria is red or pink colouring.
First stained with blue dye, then decolourised with alcohol then stained with red dye.
Describe the main differences between Positive and negative gram
Gram Positive
- Thick layer of peptidoglycan and plasma membrane
Gram Negative
- Outer membrane layer, thinner peptidoglycan and plasma membrane
Describe the following in terms of gram positive and gram negative
1) Outermembrane
2) Periplasmic space
3) Chemical composition
4) Porins
5) Lipids
6) Peptidoglycan
7) Permeability of molecules
8) Resistance to molecules
1) Present in GN only
2) Present in some GP, Present in all GN
3) Lipopolysaccharide in GN
Teichoic acids in GP only
4) Porins present in GN only
5) More lipids in GN
6) Less in GN
7) Less penetrable in GN
8) More resistant in GN
What are teichoic acids
Polymers of glycerol or ribitol joined by phosphate groups. They may bind to peptidoglycan or lipid in plasma membrane. Gives wall negative charge
What is the major feature and function of the gram negative cell wall?
Major feature is outer membrane which serves as a protective barrier. Prevents entry of bile salts and some antibiotics
How do small and larger molecules pass through the gram negative cell wall
Small molecules ie glucose pass through porins.
Larger molecules require specific carriers and secretion pathways
What stabilizes the outer membrane and contributes negative charge and also acts as endotoxin in gram negative cell wall?
Lipopolysaccharides
Give overall summary of gram positive and negative
Gram positive cell wall:
Simple structure, quite porous. Thick peptidoglycan 50nm
Cell retains crystal violet dye during Gram stain
Gram negative cell wall:
Complex structure, relatively impervious.
Thin layer of peptidoglycan 10nm
Cells don’t retain crystal violet during Gram stain
Name the 4 different optional extras and their function
Flagella for motility
Fimbriae/Pili for adhesion, gene transfer
Capsules and slime for short term survival
Endospores - long term survival
what are serotypes?
Serotypes are groups within a single species of microorganisms, such as bacteria or viruses, which share distinctive surface structures
Describe the features and functions of the extracellular structure: Pili (Fimbriae)
- Hair like appendages
- Only visible by electron microscopy
- For adhesion to other cells and each other
- On most GN and some GP
- Some cells carry sex pili, these are specialized pili involved in transfer of plasmids between bacteria
Describe the features and functions of the extracellular structures: Capsules and slime layers
- Polysaccharide material extending from cell surface
- Capsule cannot be washed off but slime layer is easily removed
- Make colonies larger and shiny
Capsules
- Protects against dehydration
- Aid in pathogenesis by protecting against phagocytosis
- Visualised by using negative staining
- Presence inferred by appearance of colonies
Describe the features and functions of extracellular structure: Endospores
- Special resistant dormant structures
- Does not replicate
- Resistant to heat, desiccation, UV, many chemical disinfectants
- Impermeable to most stains
- Sporulation normally occurs when growth ceases due to lack of nutrients and/or moisture
- Sporulation and germination are complex processes
