Unit 3.4 - microbiology Flashcards
Classification by shape
Bacillus (rod shaped)
Escherichia coli
Bacillus
Coccus(spherical)
Staphylcoccus
Streptococcus
Sprial (corkscrew)
Spirillium
Single
helicobacter
Pairs
diplococcus
pneumonide
chains
streptococcus
clusters
staphylococcus
what is gram staining?
method of staining the cell wall of bacteria to aid identification
who invented the stain?
Hans gram
who invented the petri dish?
Julian Petri
who made the agar jelly?
Fanny hesse
what does Gram stain allow?
it allows microbiologists to distinguish between Gram positive and Gram negative bacteria
how is staining different?
if the chemical composition of the wall is different
Process of staining Bacteria?
before staining, all bacteria are colourless
all the bacteria are treated with: crystal violet * a dye which binds to peptidoglycan in the cell wall and all the bacteria go purple
all the bacteria are treated with lugol’s iodine * a mordant which fixes the stain to the cell
only the gram positive remain purple and the gram negative doesn’t remain purple
ass acetone * alcohol to the gram negative ( decolouriser) which removes any crystal violet
gram negative became colourless
to the negative bacteria, ass sofranin (counter stain)
this turns the gram negative bacteria red
Features of a Gram positive
have a thick outer wall (8nm) - made of peptidoglycen/murein same thing
there is no outer lipo polyachride layer - aiming to return the dye
lipids = non polar
dye = crystal violet and therefore non soluble - stains the cells purple
What are examples of gram positives
Bacillus
Staphylococcus
Streptococcus
What do Gram positives do?
they are susceptible to pencillin
they’re killed by the enzyme lysozyme as the enzyme hydrolyses the bonds holding the peptidoglycen molecules (lysosyme is found in saliva and human tears)
What does Pencillin do?
They make their cell walls weak and therefore collapsable and Osmosis makes them burst
