Microbiology 3.4 Flashcards
what are the 4 steps of gram staining?
- Crystal violet
- Treatment with iodine
- Decolorisation with alcohol
- Counter stain with safranin
What determines the difference in a gram positive and gram negative stain
the structure of the cell wall
what are the three layers of a gram positive bacteria
- cytoplasm
- cell membrane
- peptidoglycan
How would you describe the peptidoglycan layer in a gram positive bacteria
thick
give 3 ways that you could distinguish between types of bacteria
- size
- shape
- staining characteristics
what is a metabolic feature
chemical reactions
what is an antigenic feature
surface markers
what is genetic features
different genetic features by classification
what determines the shape of a bacteria
cell wall
what makes up the cell wall
DNA
what 2 names can be given to the chemical whose rigid 3D mesh gives the bacterial cell wall its structure
peptidoglycan/ murein
why does gram positive bacteria stay purple through gram stain
because of the thick peptidoglycan layer
why is it medically important to know if a bacterium is gram positive or gram negative
to know how to treat it, they are treated differently
what does the stage of decolorisation with alcohol do to gram negative
dissolves lippopolysaccharide layer, goes colourless
what does counter stain with safranin do to gram negative
stains thin peptidoglycan layer red
what are the 3 shapes of bacteria
- cocci
- bacilli
- spirilli
what shape is cocci bacteria
spherical
what shape is bacilli bacteria
rod shaped
what shape is spirilli bacteria
spiral shaped
what are the 5 necessary conditions for bacterial growth
- nutrients
- water
- oxygen
- temperature
- pH
what are the 3 nutrients for bacterial growth
- nitrogen
- glucose
- carbon compounds
why is nitrogen so important for bacterial growth
nitrogen- amino acids - proteins - growth
what is an obligate aerobe
bacteria that grows only when oxygen is present
what is an obligate anaerobe
bacteria that only grows without oxygen present
what is a facultative anaerobe
bacteria that grows with or without oxygen but prefers with
what does the term ‘aseptic’ mean
without bacteria
give 2 reasons why aseptic techniques are used during microbiology experiments
- avoid pathogenic bacteria growing
- avoid infection
give 3 ways in which equipment can be sterilised prior to experiments
- bunsen burner
- sterile wipes
- autoclave
what pH does pathogenic bacteria grow at
pH 7 or lower
what pH does bacteria grow best at
pH5 - pH7.5
what is an example of an obligate anaerobe
E.coli because there is no oxygen in the gut
why is bacteria kept at 25 degrees in experiments
pathogenic bacteria cannot grow at this temperature
what is variable count
only counts living things
what is the total count
counts living and dead
what assumptions are made when using viable count
that each colony is 1 bacterium
how is total count measured
haemocytometry
what’s a disadvantage of total count
numbers may be overestimated
how do you measure viable count
dilution plating
what’s a disadvantage of viable count
numbers may be underestimated
what is serial dilution
progressively diluting something down by a known amount
what are 3 things you need to know in order to know how many bacteria are present
- colony number
- dilution factor
- volume of sample
what is the equation for dilution factor
total vol in tube divided by vol added to tube
what is the lag phase
- protein synthesis
- DNA replication
- steady growth
- death same as produced
what is log phase
- max cell division
- growth doubles
- cells produced= more than deaths
what is stationary phase
- carrying capacity phase
- cells dying and produced are equal
what is death phase
- more cells die than produced
- carrying capacity exceeded
what are the 3 differences that gram negative have in their cell walls that gram positive don’t
- thin peptidoglycan layer
- absence of proteins
- lippopolysaccharide layer
