Nutrition Media Flashcards
What does culture media contain?
all the elements that most bacteria need for growth
Is culture media selective or not selective? What does this lead to?
not selective –> used for the general cultivation and maintenance of bacteria kept in laboratory culture collections.
What is the proper way of saying ‘bacteria that requires a lot of things’?
fastidious bacteria
What is nutrient agar? What orgaisms does it support?
- general-purpose medium
- supporting growth of a wide range of non-fastidious organisms.
What is nutrient agar made from?
- **0.5% Peptone **- this provides organic nitrogen
-
0.3% beef extract/yeast extract - the water-
soluble content of these contribute vitamins,
carbohydrates, nitrogen, and salts - 1.5% agar - this gives the mixture solidity
-
0.5% Sodium Chloride - this gives the
mixture proportions similar to those found
in the cytoplasm of most organisms -
distilled water - water serves as a
transport medium for the agar’s various
substances
What is the pH of nutrient agar?
pH adjusted to neutral (6.8) at 25°C.
What has to be done to nutrient agar plates before inoculation?
if refrigerated for storage, the dishes must be
rewarmed to room temperature prior to inoculation.
What is nutrition agar derived from?
- jellylike substance
- derived from purifying the cell walls of red algae.
What is nutrition broth / Nutrient Broth Medium? What orgaisms does it support?
- general-purpose medium
- cultivating several less fastidious microorganisms.
How is slant agar created?
- bringing agar to the boiling point and pouring it
into a test tube. - Before the agar cools and solidifies, the test tube is set on its side.
- Once the agar is cooled, the test tube can be stored upright, and the agar
inside has a slanted appearance.
Why is ‘slant agar’ a good option?
Slanting the surface of the agar gives the bacteria a greater surface area on which to grow in a test tube.
- faster bacterial division
- easier refrigerator storage
What is “special medium blood’ agar plate? What is it used for?
-
differential media
used to: - isolate fastidious organisms,
- detect hemolytic activity.
What are the three types of hemolytic activity? What do they signify?
β-Hemolytic activity:
- lysis and complete digestion of red blood
cell contents surrounding a colony.
- eg. Streptococcus agalactiae.
α-Hemolytic activity:
- partial lysis of the red blood cells (the cell
membrane is left intact)
- appears green or brown, due to the conversion of hemoglobin to methemoglobin.
- eg. Streptococcus viridans
γ-Hemolytic activity:
- nongemolytic activity
- lack of hemolytic activity
What is Mannitol Salt Agar (MSA)?
- selective and differential medium,
- genus Staphylococcus (other genera may grow but very weakly!)
- high salt concentrations (7.5%)
What colour does Mannitol Salt Agar change into? What does this allow us to differentiate?
phenol red –> yellow
- organisms ferment mannitol –> acidic byproduct formed
- Staphylococcus aureus (pathogenic S.) ferments mannitol = yellow
- Staphylococcus epidermidis (non-pathogenic S.) doesnt ferment = red
What is Drigalsky lactose agar? What is it used for?
- used for the selective isolation of enterobacteria,
- differentiated on the basis of wether they can ferment lactose or not.
How are organisms differentiated using Drigalsky lactose agar?
Lactose fermentation: –> production of acid, bromthymol blue –> yellow.
Non-lactose fermenting (enteric) pathogens form
blue/green colonies whereas lactose
fermenting coliform organisms form yellow
colonies.
What is Eosin methylene blue (EMB) media used for?
- isolation medium
- differentiation of the Enterobacteriaceae.
What is special about Eosin methylene blue (EMB)?
contains dyes that are toxic to gram-positive bacteria.
- dyes colonies that ferment lactose (dark center (nucleated))
What happens when E. coli is grown on EMB?
E.coli –> metallic green stain –> the metachromatic properties of the dyes, E. coli movement using flagella, and strong acid end-products of fermentation.
What is Eosin MacConkey agar used for?
- selective and differential culture medium
- for bacteria
- isolate Gram-negative and enteric bacilli
- differentiate them based on lactose fermentation
How does Eosin MacConkey agar allow for selection?
- The crystal violet and bile salts inhibit the growth of grampositive organisms
- pink medium becomes hazy
What are non-lactose fermenting bacteria?
Salmonella, Proteus species, Yersinia, Pseudomonas aeruginosa and Shigella.
What is TBX? What is it used for?
Tryptone Bile Agar
- selective, chromogenic medium
- detection and enumeration of Escherichia coli
- detects glucuronidase (X-glucuronide) activity.
- clear –> green
