3. Bacterial shape, size and appendages Flashcards
Gram positive
Aionic polymers in their walls
Techoic acids
Has important function but no understanding
Antigenic = immune response triggered
Key structures of Gram positive bacteria
Single cytoplasmic membrane
Large external cell wall
Cell wall from peptidoglycan
Gram negative
Has extra lipid bilayer
Outer membrane contains periplasm and lipid polysaccharides
Periplasm = contains cytoplasmic membrane and layer of peptidoglycan
Lipids extend through membrane
Lipid = A pyrogenic endotoxin - produces fever
Defense system against immune system - sheds lipopolysaccharide layer and replaces with unrecognisable layer.
Protinaceus S layer
The outermost layer of cell envelope Present in most bacteria and archaea Crystalline structure lattice of single protein Protective selective sieve Often lost I lab strains
Capsules
Usually polysaccharides
Sometimes covalently attached to cell wall
necessary for biofilms
Can be immunogenic and help with immune response
Protects against phagocytosis
Usually attached to flagella / pili and fimbriae
Pilli and fimbriae
Surface appendages Protein polymers Used for attachment and adhesion Important for pathogenesis Immunogenic Supports gene transfer via conjugation Twitching motility
Flagella
Rotary motor
Biological nanomachine
Rotation and helical structure generates movement
Chemotaxis gives directionality - ensures movement to attractants and away from repellants
Random biased walk
Endospores
Provides ultimate survival mechanism
Triggered by starvation
Resistant to heat, solvent and lysozyme
Remains dormant for centuries
Germinated when favourable conditions return
Interesting model for cellular development
Sporulation
Involves sophisticated 2 cell differentiation process.
σE/σF - Controls sporulation gene expression in different places
σE - Only in mother cell
σF - Onlyin prespore
Stage 2 cell division: cell committed to endospore
Biofilms
Communities often multiple species together
Held together by matrix: mainly polysaccharides, protein and nucleic acid
Causes medical complications and dental plaque
SWIM -> SESSILE
GROWTH -> SPORULATION
Produces adhesion and resistance to antibiotics and desiccation.
The gram staining method
Distinguishes between major pathogenic organism.
Based on membrane presence on gram negatives.
- Flood heat fixed smear with crystal violet for 1 min (All cells purple)
- Add iodine for 1 minute (All cells purple)
- Decolourize with alcohol for 20 secs (Gram positive cells purple, gram negative cells colourise.
- Counterstain with sefranin for 1-2 mins (Gram positive cells purple and gram negative cells pink/red)
Electron microscopy
Unpredicted resolution
Cells fixed, dehydrated, embedded, sectioned and stained before hand
Single compartment - no nuclear envelope
Featureless cytoskeleton with no obvious organelles
Lack of compartmentalization or regional specialization.
Cyro electron microscopy and tomography
Avoids artifacts Samples flash frozen from 'live' state Fixation, embedding and sectioning not needed Obtains 'tiH' series at very high power 3D construction
Poor contrast
600nm depth limits
Green fluorescent protein / GFP tagging
Genetic manipulation to make protein-GFP fusion
Enables live cell, time lapse imaging
Many colour variants: allows simultaneous visualisations of different proteins
Many proteins malfunction
Localization can be misleading
Fluorescence microscopy and digital imaging
Imaging via high power optimising lenses
Specific cell component visualised with fluorescent dye - Immunofluorescence or GFP tags
Digital detection with superfast high resolution cameras
