Microbiology Flashcards
Function of the bacterial cell wall
strong outer cover that maintains bacterial shape & protects against osmotic pressure
Ways bacteria may use its morphology to survive (3)
- having a **capsule** that protects against phagocytosis
- flagella (longer) or pili / fimbriae (shorter) that enables them to move or deliver toxins to host
- **two membranes** for protection
Describe the variations in cell wall structure accounting for gram-positive and negative staining
pos = single ; neg = double
gram positive = thick, single peptidoglycan layer made of repeating sugar subunits cross linked by peptide chains in cell wall
gram negative = thin peptidoglycan layer & an additional outer membrane containing lipopolysaccharides = endotoxins
Function of flagella on bacteria
allows for movement
Function of fimbriae / pili on bacteria
- allow bacteria to adhere to cell surfaces & exchange plasmids with other bacteria
- allows for the delivery of endotoxins to host (?)
Ways bacteria can be classified
Shape, staining, biochemical tests, sensitivity tests & culture techniques
Round, spherical bacteria are known as?
Coccus / cocci
Rod bacteria are generally known as?
Bacilli
Curved rod bacteria are known as?
vibrio
Spiral rod bacteria are known as?
spirochaete
Temperature range for bacterial survival, and for spores>
-80 to +80 degree Celcius, spores = up to 120 degree Celcius
How do you measure growth rate of bacteria?
Measured by shining light on bacteria and measuring absorption
Briefly describe the three ways bacteria performs gene transfer
- transformation - pick up DNA from environment - via plasmid
- transduction - when virus infects bacteria - via phage
- conjugation - exchange of plasmid between bac cells - via sex pilus
How does bacteria achieve genetic variation (3+3)
- mutations: baseline substitution, deletion, insertion
- gene transfer: transformation, transduction, conjugation
How does the gram stain differentiate bacteria?
PINK = negative = double membrane bacteria = endotoxins and exotoxins
PURPLE = positive = single membrane bacteria = exotoxins only
Briefly describe the gram staining technique?
- heat fix sample to slide
- add methyl violet (blue / purple)
- add iodine → fixes methyl violet to gram pos samples
- add alcohol to decolorize gram neg samples
- counterstain with basic fuschin (red)
What does it mean if the gram stain returned positive?
- sample will be purple
- sample is a single membraned bacteria which will produce exotoxins only
What does it mean if the gram stain returned negative?
- sample will be pink
- sample is a double membraned bacteria which will produce both exo and endotoxins
What are endotoxins?
- Component of the outer membrane of bacteria that is released when bac is damaged
- Specific components of this is recognised by the immune system → will have huge reaction = endotoxic shock
- Work is non-specific
What are exotoxins?
- proteins secreted by both bacteria.
- action is specific: inhibit (botulism) or stimulate (tetanus) nervous system
- unstable exposure to heat
- can be converted to a toxoid → non-active toxin
What colour will the bacteria stain with Gram stain if it only produces exotoxins?
Purple = gram-positive bacteria = single membrane
What colour will the bacteria stain with Gram stain if it produces both endotoxins and exotoxins?
Pink = gram-negative bacteria = double membrane
When should you not use the gram stain to group bacteria (i.e. when will it not work)
- for cell walls that contains mycotic acids (‘acid fast bacilli’) which the gram stain cannot get in to
- e.g. mycobacteria spp.
→ Ziehl-Neelsen staining should be used
What stain is used for mycobacteria spp.?
Ziehl-Neelsen staining
result = red or blue