Microbiological Culture Media Flashcards
What is a solid media?
There is liquefiable media- this contain thermoplastic agents such as agar and gelatin.
Non-liquefiable- eg. silica as gelling agent or use of natural products such as grains, potato slices, cooked meat etc.
What is the most important thermoplastic gelling agent and why?
Agar is the most important thermoplastic gelling agent because it is inert, stable once gelled and inexpensive.
What is liquid media also known as?
It is also known as broth media
What is semi-solid media?
it contains a small % of agar (usually less than 0.5 %) and it is used for bacterial motility, biochemical tests, growing microaerophiles.
What are the two major classes of media?
- Chemically defined Media (synthetic)
2. Complex or undefined media (non-synthetic)
What is chemically defined media?
constituents and their exact concentrations are known. it can be used for metabolic/physiological/genetic studies or production of metabolites.
What is complex media?
The exact chemical composition of these media are not known. it can include plant and animal tissue extracts. it can be used to support the growth of most heterotrophs and are nutrient rich.
What are artificial complex media examples?
it can include natural extracts such as malt or meat, peptones or yeast extract.
What are natural examples of complex media?
It can be obtained from natural sources and can include fruit juices.
These natural products are used as the media without modifications.
What is general-purpose media?
It has multiple functions such as for storage, enumeration, isolation and general culture, an example of this is nutrient agar.
What is selective media?
It is used for isolation of specific types/groups of microorganisms.
It contains substances that can inhibit the growth of specific types/groups of bacterium while permitting the growth of other.
an example of this is MacConkey agar is used to isolate Gram negatives contains crystal violet which tends to be inhibitory towards most gram positive bacteria.
What is differential media?
It is used to distinguish among morphologically and biochemically related organisms.
it contains compounds that either produce a change in the appearance of the organism cultured or the surrounding medium.
What is an example of differential media?
an example is thioglycolate broth and it is used to differentiate oxygen requirement levels of various microbes.
A reaction with sodium glycolate in the medium reduces oxygen availability,
Gradual decrease in oxygen concentration with increased distance from the surface of the media.
The presence of oxygen in the media is indicated by a pink colour change.
Aside from thioglycolate broth, what is another differential media?
MacConkey agar
- apart from bile salts contains lactose and pH indicator (neutral red)
- organisms that have the ability to ferment lactose produce acid and therefore appear red at the surface.
- By contract, non-lactose fermenters remain uncoloured since they do not produce acid.
What is minimal media?
- This chemically defined medium contains minimal requirements for growth
- it does not support the growth of some or all auxotrophic strains of a given organism.
- only growth of prototrophic strains is permitted
- often used in metabolic studies and in taxonomic descriptions of organisms.
What is enriched media?
- These media are supplemented with highly nutritious materials such as blood, serum, yeast, and extract.
- mainly used for the cultivation of fastidious organisms.
- Blood agar which contains blood as an enrichment ingredient is used for the culture of members of the Streptococcus genus.
- Blood agar also allows the classification of streptococci based on their haemolytic activities such as gamma haemolysis, alpha haemolysis and beta haemolysis.
Enrichment Media
Broth medium containing substances that allow target group to multiply before plating onto selective or differential agar.
Transport media
- maintains specific conditions for stabilizing cells during transport to lab
- Cary-blair semi-solid transport medium
Enumeration media
- used for accessing or monitoring the total and/or viable cell count.
- Plate count agar and RZA are two examples.
Assays
- used to measure specific biochemical
- Example- resistance to antibiotics
What does medium influence?
- rate of cell growth/proliferation
- Metabolic pathways utilized, hence metabolites produced.
- Gene product quantity (regulation of gene expression
What is medium optimization?
Medium optimization studies involve the construction of growth curves to monitor cell proliferation rates.
why culture preservation is crucial?
- This allows a stock of producer cells to be maintained:
1. For use over a long period of time
2. As a backup in the event of errors in the process or losses due to contamination.
3. As a reference for regulatory bodies/scientists performing checks (traceability & accountability.
What do culture preservation techniques need?
They all require GOOD ASEPTIC technique.
