Growth and identification of bacterial pathogens Flashcards
Bacterial cells
Bacteria are 10x smaller than eukaryotic cells, what does this allow for
-rapid metabolism
-diffusion of nutrients is not limiting like in eukaroytes
– they can do rapid turnover of sugars, amino acids, and nucleotides
- which can help them build DNA n RNA
Bacterial growth
Why is bacterial growth under optimal conditions not a good thing?
They grow rapidly
but as a consequence this can cause sepsis (if your not quick with your antibiotics)
Media
What is microbiological media?
Liquid culture
Media
What do we use Microbiological media for?
- Used to quantify growth rate (to see how quick they grow)
- Study physiology of bacteria
Media
What is solid media?
Basically uses agar
Media
What is the use of solid media
- Preliminary identification
- Can work out the number of live bacteria
- Can isolate a pure culture (1 colony)
- so that there is no contaminants
Media
What is the use of selective media
- Isolate specific bacteria,
- inhibits growth of other bacteria
Media
What is the use of differential media
- Ability to distinguish between different bacteria
- see a difference between each other
Media
What is the use of macconkey agar
- this is both selective and differential
- inhibits the growth of bile salts and crystal violets
- because bacteria don’t like growing in situations like this
Media
For macconkey agar we can use a pH indicator, what do the different colours represent?
below pH 6.8 = pink
neutral pH = colourless
Media
If we used macconkey agar to look at ecoli and salmonella?
What happens?
- Ecoli forms pink columns
- ferments lactose so pH drops so it changes colour
- Salmonella does not ferment lactose (so it stays neutral)
Media
What do growth mediums need to contain?
-Carbon: In the form of glucose or other sugars
-Nitrogen: Anorganic (ammnonia, nitrate), or organic (like amino acids)
-Sulphur: (essential for amino acids)
-phosphorous: (required for ATP, DNA, RNA taken up as a inorganic phosphate)
-Minerals (Fe2+,Mg2+,Ca2+) -> needed for enzyme function
Media
What is a defined medium?
- pure chemicals → means its very reproducible
- used for ecoli
- we know exactly what in this medium
- it’s like a recipe, we know if you put in these exact amounts ecoli is going to grow
Media
What is complex media made from
- Digests of microbial, plant and/or animal products
- like marmite, or chicken stock
- dehydrated infusion or porcine brains and hearts
Media
What does complex media support the growth of?
just think simply
lots of different bacteria
Microbial growth
What factors determine microbial growth?
just list them for now
-pH
-oxygen
Microbial growth
How does pH determine microbial growth?
What is optimum growth pH
- Grow optimally at neutral pH ( 7.4)
Microbial Growth
What are the expceptiosn to bacteria that like growing at lower pH
Give an example and how it does it
h pylori
- causes stomach ulcers and grows at pH 3
-How does it do this?
-creates a micro-enviorment around the stomach, which has a more neutral pH
- it does this by producing ammonia and bicarbonate
Microbial growth
The second factor that affects growth is oxygen?
How does o2 do this?
-aerobic bacteria breathe using mircobial respiration
- which is the best way to make ATP energy
Microbial growth
Some bacteria don’t need oxygen, what are these bacteria called?
Type of bacteria
- Aerotolerant anaerobes: can tolerate and grow in air
- Obligate anaerobes: oxygen inhibits the growth of these guys or kills them
- in the gut, a vast majority are obligate anaerobes
Anaerobes: don’t need respire oxygen
Microbial growth
How do obligate anaerobes in the gut survive when they get excreted out?
- they create spores
- these can tolerate high heat, oxygen, UV
- this structure protects DNA in the cell
- when they are in environments that can facilitate their growth, they germinate
Microbial growth
How do bacteria grow?
What are the 4 phases
-Lag
-Exponerial
-staionary
-death
Microbial growth
What happens in the lag phase?
- Need to adapt to new environments
- need to start metabolising
- generate ATP, ribosomes
Microbial growth
What happens during the exponential phase?
- divide every 20, to 30 minutes
- rapid cell growth and metabolism
- cells run out of one or more nutrients,
- due to waste products limiting growth since there’s so many of them
- these waste products can then accumilate
Micorbial growth
What happens in the stainoary phase
Expand on the points as well
- no more growth
- slow growth
- start preparing for survival (so can make spores)
- they are resistant to stress because they switch on all sorts of defence mechanisms
- harder to treat, maybe more resistance to antibiotics
- they also produce antibiotics to kill their neighbouring cells
- if you kill the neighbouring cells, then you can take their nutrients, and recycle them, to grow you’re self
If you did not get the explanations rate this 2
Microbial growth
What happens in the death phase?
they die because they have no nutrients to grow
Identifying bacteria
How do we identiy bacteria using the gram stain
- You first use crystal violet,
- and then wash it out with ethanol,
- and then positive bacteria will retain the crystal violet so we can see them
- with gram negative since we cant see them
- so we stain them using safranin
identifying bacteria
The gram stain allows us to visualise bacteria, How do we classify these bacteria?
- Gram negative bacteria (light pink)
- Gram-positive bacteria (dark purple)
Identifying bacteria
What’s the difference between gram negative and gram positive bacteria
Gram-positive bacteria
- have a single cell wall
- but have a larger layer of peptidoglycans
Gram-negative bacteria
- have two membranes
- but a thin layer of peptidoglycans
Why is it important to use gram stains
like how does it help us and what are the implications of some bacteria
- use it to premlimnary identify bacteria
Why?
- important because differences in cell wall, has impact on what antibiotics we can use
Identifying bacteria
Gram negative bacteria are more resistant to antiboitics than gram poistive.
Why?
Gram negative bacteria only few antibiotic, can target that second cell wall
Clinical microbiology
What is direct microscopy and what are the advantages
standard light microscope
staining
Advantages
cheap
fast
useful in low-resource settings
