3.4 Microbiology Flashcards
How is bacteria classified ?
By shape, size and cell wall structure
What are the different shapes of bacteria ?
Bacillus, Cocci, Spiral
Name a type of bacillus bacteria
Bacillus or Eschericha
Name a type of cocci bacteria
Staphylococcus
Name a type of spiral bacteria
Spirillum
What does gram staining allow ?
Enables you to distinguish between gram positive and gram negative bacteria
What are the stages of gram staining ?
Use crystal violet reagant as basic dye, Iodine to flood slide, acetone to decolourise and safranin as a counter stain
What does crystal violet do in the gram staining process ?
Binds to peptidoglycan so all bacteria stains purple
What does iodine do in the gram staining process ?
Acts as a mordant binding crystal violet to peptidoglycan more strongly
What does acetone alcohol do in gram staining process ?
Acts as a decolouriser removing unbound crystal violet and lipopolysaccharide
What is the purpose of safranin in gram staining ?
Acts as a counter stain
What colour does gram positive bacteria stain ?
Purple
What are the features of gram positive bacteria ?
Thick peptidoglycan layer
Cell membrane
No lipopolysaccharide layer so susceptible to penicillin and lysozyme enzyme
What colour does gram negative bacteria stain ?
Pink/Red
What are the features of gram negative bacteria ?
Lipopolysaccharide, peptidoglycan and cell membrane layers
What is the purpose of the lipopolysaccharide layer ?
Protect the cell
What are the different types of culture medium ?
Defined
Undefined
Selective
Complete
What is a defined culture medium ?
Only contains known ingredients
What is an undefined culture medium ?
Contains components that are not all known
What is a selective culture medium ?
Only allows certain bacteria to grow
What is a complete culture medium ?
Contains all chemicals needed to support growth
What is required for bacteria growth ?
Carbon
Glucose
Nitrogen
Vitamins
Minerals
25-45 degrees, optimum 37
pH 7.4
Oxygen
What are the 3 different types of bacteria ?
Facultative anaerobes
Obligate aerobes
Obligate anaerobes
What is a facultative anaerobe ?
Bacteria that grows best with oxygen but can survive without
What is an obligate aerobe ?
Bacteria that requires oxygen
What is an obligate anaerobe ?
Bacteria that cannot grow in the presence of oxygen
What is aseptic technique ?
Laboratory practise that maintains sterility in apparatus and prevents contamination of the equipment and environment
What methods can be used to measure growth ?
Direct counting of cells
Indirect measurement
What are the 2 ways to directly count cells ?
Viable counts
Total counts
What is a viable count ?
Count colonies of living cells
What is a total count ?
Using a haemocytmeter
How do you indirectly measure growth ?
By measuring the turbidity of a culture
What is turbidity ?
Cloudiness
How do you plate and count colonies ?
Count number of cells in small sample of culture
Viable count - live cells
How do you calculate population size ?
(Number of colonies X Dilution factor ) Divided by Volume of sample
