3.4 - Microbiology Flashcards
What are the 3 main types of shapes in bacteria and an example of each?
Bacillus or rodshaped eg Bacillus
Coccus or spherical eg Staphyloccus
Spiral or corkscrew shaped eg Spirillum
Example of single bacteria.
Helicobacter
Example of a bacteria in pairs.
DiplococcusE
Example of a bacteria in chains.
Streptococcus
Example of bacteria in clusters.
Staphylococcus
What is a gram stain?
A method of staining the cell walls of bacteria as an aid to their identification
Allows us to distinguish between gram neg and gram pos
Before staining, bacteria are colourless, g+ are stained purple, g- are stained red
What does the cell wall do in bacteria?
Peptidoglycan
Provides strength and gives it shape
The wall protects against swelling and bursting from lysis
G+ have a basic structure, whilst G- have an outerlayer of polyscaccharide
What are the 4 stages behind gram staining?
Crystal violet reagent - basic dye (Binds to peptidoglycan so all bacteria stain purple)
Lugols iodine - mordant (binds crystal violet to the peptidoglycan more strongly)
Acetone alcohol - decolouriser (removes unbound crystal violet and lipopolysaccharide, g- lose their stain and become colourless, g+ remain purple)
Safranin - counterstain (g- stain red, g+ remains purple)
What does it mean the g+ bacteria have no lipopolysaccharide?
No lipopolysaccharide makes them more suseptible to lyzosome and penicillin
What does it mean the g- bacteria have lipopolysaccharide?
They are resistant to penicillin and lyzosome
To control them, a different class of antibiotics are required that interfere with protein synthesis
How do bacteria reproduce?
Asexually through binary fission every 20 mins
What do micro-organisms require for growth?
- nutrients
- vitamins and minerals
- correct temperature (25-45)
- pH alkaline conditions
- oxygen to grow (some can survive without it)
What is a defined media?
Contains only known ingrediants
What is an undefined media?
Contains components not known
What is a selective media?
Allows certain bacteria to grow
What is a complete media?
Contains all chemicals needed to support growth
What is aseptic technique?
Laboratory practice that maintains sterility in apparatus and prevents contamination of equipment and the environment
How does the aseptic technique method prevent contamination?
- sterilise all apparatus
- handle all cultures carefully
-sterilise work surface - hold the culture bottle with one hand, remove the cap with little finger of the other hand, do not place cap down on the worksurface
- flame the mouth of the bottle for 2-3 seconds
- pass the inoculating loop through the flame until it is red hot and allow it to cool in the air
- lift the lid of the petri dish just enough to allow entry of the inoculating loop
- secure the petri dish with 2 pieces of tape to prevent anaerobic conditions (growth of pathogens)
- incubate at 25*
How can the size of a population be measured?
Directly by counting cells
Indirectly, by measuring the turbidity (cloudiness) of the culture
What is the difference between total cell counts and viable cell counts?
- viable counts (living cells only)
- total counts (living and dead)
What is a colony?
A cluster of cells, or clone, which arises from a single bacterium or fungal spore by asexual reproduction
How are serial dilutions created?
9cm3 water in a test tube
Take 1cm3 of orginal solution and put it in first test tube
Creates a 10-1 solution
Repeat until desired dilution is acquired
Why are most bacterial cultures diluted?
So that clumping doesnt occur on the agar plates, so colonies can be counted.
What is the equation for a dilution factor?
dilution = 1/conc
What is the equation for population size?
population size = number of colonies x dilution factor/ volume of the sample
What is a haemocytometer?
It is more accurate than other counting techniques as it uses a specialised microscopic slide called a haemocytometer, result is a total cell count.
