Growth and Nutrition of Bacteria Flashcards
What is a bacterium?
Bacterium are microscopic living organisms, usually one-celled, that can be found everywhere. They can be dangerous, such as when they cause infection, or beneficial, as in the process of fermentation (such as in wine) and that of decomposition
What is the role of beneficial bacteria?
90% of cells in a human are bacterial
Education of the immune system, possible role in allergy
Importance of the microbiome in health
List some of the different morphologies of bacteria
coccus rod spirillum spirochete budding and appendages bacteria (stalk and hypha) filamentous
How are slides prepared to visualise bacteria?
Spread culture in thin film over slide Dry in air Pass slide through flame to fix Flood slide with stain; rinse and dry Place drop of oil on slide; examine with 100x objective
Describe the steps and the stains used in differentiating gram positive and negative bacteria
1 = Flood the heat-fixed smear with CRYSTAL VIOLET for 1 min (all cells PURPLE)
2 = Add IODINE solution for 3 min (all cells remain PURPLE)
3 = Decolorize with ALCOHOL for about 20 seconds, POSITIVE=PURPLE, NEGATIVE=COLOURLESS
4 = Countertain with SAFRANIN for 1-2 min.
POSTIVE=PURPLE
NEGATIVE=PINK
Describe the different cell wall structures between gram positive and negative bacteria and how this affects staining.
Gram positive - One membrane - Thick peptidoglycan layer Gram negative - Double membrane - Thin peptidoglycan layer - heavily modified outer membrane (LPS/endotoxin)
How do bacteria cause disease? x5
- Attachment - bacteria usually need to attach to human cells to cause disease
- Invasion - some pathogens invade human cells Intracellular pathogens such as TB and Salmonella
- Acquire nutrients in the host e.g. iron
- Evade the immune system to survive
- Cause damage to the host (reflection in disease symptoms)
What is gram negative shock?
Gram negative bacteria have heavily modified outer membrane with lipopolysaccharides (endotoxins) These trigger an immune response which can lead to shock.
How do bacteria attach to host cells?
Bacteria use specialised appendage and surface molecules to stick to human cells
This can affect subsequent fate of the bacterium
What mechanism does enteropathogenic E.coli use to enter host cells?
Molecular syringes
How do bacteria invade a cell?
Type 3 secretion systems can also be used to promote bacterial invasion by injection of ‘effector molecules’ into host cells
These molecules then alter cell cytoskeleton and promote bacterial uptake
The best example is Salmonella Typhimurium
Describe an example of how bacteria acquire nutrients from their host.
An example is iron. The host withholds iron by binding to high affinity carrier e.g. lactoferrin and transferrin
Bacteria make molecules called siderophores that can scavenge iron from host molecules
Alterations in iron physiology can increase susceptibility to bacterial infection
Give some examples of how bacteria can evade the immune system.
- inhibition of phagocytosis
- induction/inhibition of apoptosis
- blockade of cell cycle progression
- inappropriate t cell activation
- decreased susceptibility to antibiotic peptides
What are the two main mechanisms by which bacteria damage their host?
- Direct - usually mediated by production of coins such as membrane damaging toxins, enzymes and neurotoxins. Some diseases are largely toxin mediated e.g. cholera
- Indirect - over-activation of immune system e.g. bacterial lipopolysaccharide (LPS) over-activation of cytokine production during sepsis. Molecular mimicry
What is sepsis?
blood poisoning
blood infection
