Study Set Content:
However, there are also microorganisms that can’t grow on a culture media at all in any condition – these are called
obligate parasites
is essential for diagnosing infectious diseases, obtaining antigens, developing serological assays for vaccines, genetic studies, and identification of microbial species
Culturing microorganisms
: In these media, the agar which is an unbranched long chain of polysaccharides is added in the concentration of 1.5-2.0%. Most commonly, 1.3% agar is used to prepare solid media in labs. The agar-containing media solidifies at 37 ºC. [1] Sometimes, in the place of agar, some other inert solidifying agents are used, such as gellan gum.
Solid media
are used to grow microorganisms in their full physical form, prepare bacterial pure cultures, or isolate bacteria to study colony characteristics. [1] The bacterial growth on solid media varies in appearance as mucoid, round, smooth, rough, filamentous, irregular, and punctiform. The media is not hydrolyzed by microorganisms and is free from growth-inhibiting substances
Solid media
This media has 0.2-0.5% agar concentration, and due to the reduced agar concentration, it appears as a soft, jelly-like substance. It’s mainly used to study the motility of microorganisms, distinguish between motile and non-motile bacterial strains (through U-tube and Cragie’s tube), and cultivate microaerophilic bacteria – bacteria on this media appear as a thick line.
Semisolid media
: These media do not contain any traces of solidifying agents, such as agar or gelatin, and large growth of bacterial colonies can be observed in the media. Liquid media are also called broths, they allow for uniform and turbid growth of bacterial strains when incubated at 37ºC for 24hrs. The media is used for the profuse growth of microorganisms and fermentation studies
Liquid media
blood agar, nutrient agar, McConkey agar, and chocolate agar
solid media
Hugh and Leifson’s oxidation fermentation medium, Stuart’s and Amies media, and Mannitol motility media
semi-solid
Tryptic soy broth, phenol red carbohydrate broth, MR-VP broth, and nutrient broth.
Liquid media
, which consist of both solid and liquid media
biphasic media
are added to the media as a solidifying agent.
place of agar, egg yolk and serum
While naturally, these substances are liquid, they are solidified by using heat, and the prepared media is
sterilized using the
inspissation technique
It’s a general-purpose media that supports the growth of non-fastidious microbes, and it is primarily used for the isolation of microorganisms. Examples are nutrient broth, peptone water, and nutrient agar
Simple media
These are media containing nutrients in unknown quantities that are added to bring about a particular characteristic of a microbial strain. Examples are tryptic soy broth, blood agar, and nutrient broth.
complex media
is a type of chemically defined media and is produced from pure chemical substances. A defined media refers to a medium having a known concentration of ingredients, like sugar (glucose or glycerol) and nitrogen source (such as ammonium salt or nitrate as inorganic nitrogen). It is generally used in scientific research, and an example is Czapek Dox Medium.
Synthetic media
These are routinely used simple media having carbon and nitrogen sources that boost the growth of many microorganisms. They are also known as general-purpose media and are considered non-selective media.
Basal media
do not require enrichment sources for the growth of non-fastidious bacteria and are suitable for growing Staphylococcus and Enterobacteriaceae
basal media
This media is prepared by adding additional substances like blood, serum, or egg yolk in the basal medium. It’s used to grow fastidious microorganisms as they require additional nutrients and growth-promoting substances.
Enriched media
This media allows the growth of certain microbes while inhibiting the growth of others. It’s an agar-based medium that is used to isolate microorganisms in labs.
Selective media
The selective growth of microbes is decided by adding substances like
antibiotics dyes, bile salts, or pH adjustments
