General microbio Flashcards
(20 cards)
General description of a bacteria ?
- Small self replicating organism
- Prokaryotes
- no real nucleus
- No compartment of the cytoplasm - Total mass of the bacteria of human beings : approx 700g
What do organisms need to replicate?
Genetic material/information (DNA or RNA)
Need organelles to replicate (ribosomes)
- (Viruses have no ribosomes)
What are some differences between prokaryotes and eukaryotes?
Prokaryotes:
- Diameter of 1-5 um
- Have a nucleoid (something equivalent to a nucleus, but no membrane)
- They have plasmids (extra chromosomal DNA)
- 70S ribosomes
- Cell wall containing peptidoglycan
Eukaryotes:
- 5 um and larger
- Nucleus containing membrane
- 80S and 60S ribosomes
- Endoplasmic reticulum, golgi apparatus
- Lysosomes
- Mitochondria (70S ribosomes)
- Some have no cell wall, cell wall of fungi and plants always without peptidoglycan
Name some structures of the bacteria
Cytoplasm
Nucleoid
Ribosomes
Cell wall = > Cytoplasmic membrane + capsule
Pili
Flagella
Describe the capsule
- (Bacillus anthracis, Streptococcus equi subsp. equi. )
- Contains extracellular substances (glutamic acid, hyaluronic acid)
- Protection against dehydration
- Permeability barrer )e.g. antibiotics)
- Increasing adhesion
- Protection against phagocytosis (performed amongs other by macrophages and monocytes)
- biofilm
Give features of the flagella
- Motility of bacteria
- Makes Taxis possible (able to move)
- Can be indicator of virulence factor
- Antigens can be found on the flagella (can be used in the diagnosis/differenciation of bacteria. Ex: salmonella types)
- Powered by protons (1000 protons/rotation)
What type of taxis is the bacterial taxis?
Chemotaxis.
Can attract/repell
=> bacteria can move to attractant , move away from repellants
Name and describe 2 attachment structures
Fimbriae
- 20 um lon protein filaments
- 10-1000 per cell
- Adhesion organelles (adhesin)
- F-antigens
Pili
- Tubular hair-like protein structures
- 1-2 per cell
- F-pilus, sexpilus => conjugation
What is the function of the cell wall?
- Shaping exoskeleton
- Permeability barrier
- Adhesion to host cells
- Virulence factors
- Antigens
What is the matrix of the cell wall made of?
- Peptidoglycan, murein
- A peptidoglycan monomer is composed of : N-acetylglucosamin and N-acetylmuramic acid (NAM-NAG)
- Also additional cross-linkages through oligopeptide side chains
What is the difference between a gram - and gram + cell wall?
Gram +:
- Cytoplasmic membrane (phospholipid bilayer)
- Peptidoglycan (10-40 layers)
Gram -:
- Inner membrane (phospholipid bilayer)
- Peptidoglycan (1-3 layers)
- Outer membrane
- LPS (lipopolysaccharides)
In what type of bacteria do you find the LPS layer (lipopolysaccharide). Gram - or Gram +?
Describe this LPS layer and its implication in infections
Gram -
LPS has 3 parts:
- Lipid anchor (lipid A). Part of the outer membrane of the gram negative bacteria. Also is an endotoxin, pyrogen.
- A core region. 5 sugar molecules
- O-specific side chains. Repetitve unnits of oligosaccharides. O-antigens (somatic antigens). Are heat stable, serotyping.
As soon as the cell is destroyed (ex: antibiotics etc.), the lypopollysaccharides (toxin) is released and can harm the body. Therefore, an infection to a gram - bacteria can cause more trouble than infection to a gram + bacteria. (réécouter la slide sur le LPS)
Describe the nucleoid
- Bacterial chromosome
- Can be circular or linear
- Is double stranded
- Is free in the cytoplas, only few proteins (histones)
- Contains the housekeeping genes
- Mostly single copy genes: no compensation after mutation by homologous genes possible (so if mutation, cell dies/stops replicating)
- One of the model is E. Coli, has 1000 encoding genes
How does the nucleoid organize itself in the bacterial cell?
Explain
By supercoiling.
DNA Gyrases makes the DNA curl => topoisomerase II
What does the bacterial cell use to “relax” the supercoils?
Topoisomerase I
Name a gyrase inhibitor. What is the implication of a gyrase inhibitor?
Chinolones
=> Can cause irreversible disruption of the DNA replication
DNA gets longer and at some point destroyed because of the uncoiling of the DNA. Bacteria can’t replicate because of this. Dies.
Where is the DNA contained in the bacterial cell?
Nucleoid and plasmid
Describe plasmids
- Extra chromosomal DNA => non-essential
- Circular or linear
- 100 to 1000 kpb
- 1 to 100 copies per cell
- Replication independent from the nucleoid
- Often implication with virulence/resistance genes
- conjugative plasmids => control their own transfer
- Implication in molecular biology = cloning vector (ex ATB)
What is the Ziehl-Neelsen-staining for?
- Special staining for mycobacterium
- These bacteria have a special cell wall that protect them from acids.
- Tuberculosis is an example.
- Takes 8-12 weeks to grow
What are the steps in gram staining?
What colour do the different types of cell have after each step?
- Air-dried, heat fix the bacterial specimen to the slide
- Both cell types are translucent still - Gentian violet, 2 min
- Both are blue/purple - Removal of the dye
- Both translucent - Lugol solution, 2 min
- Both blue/purple - Removal of the dye
- Both translucent ? - Discoloration using ethanol
- Gram + : blue. Gram - : translucent - Counterstaining with safranin :
Gram +: purple/blue. Gram - : red/pink
