Inanimate Media

Inanimate media describes any media that is not living. This includes things that came from a living organism, such as milk, or things that were once living but has since passed away. Inanimate media can be either nonsynthetic or synthetic.

Nonsynthetic Media
Nonsynthetic natural media may be the only type of medium that an organism will grow on, like truffles, for example, and are cheap enough for commercial applications, like mushroom farms. However, it is not chemically defined, and is not sterile.
 * Milk
 * Grows heterotrophs
 * Culturing bacteria in milk makes yogurt
 * Dead branches
 * Grows heterotrophs
 * Grows mushrooms
 * Soil
 * Contains inorganic and organic nutrients
 * Helps grow both heterotrophs and autotrophs
 * Grows mushrooms or algae

Hot Water Extracts
Hot water extracts is like making tea but with nonsynthetic material. BHI are sterile, and can be made from many sources, like pond water or soil. However, it still has unknown elements in it and fewer organisms will grow on it compared to the normal nonsynthetic media.
 * Brain Heart Infusions (BHI)
 * Cow brains and hearts are boiled and then the remaining liquid is evaporated. The remaining powder is autoclaved and then sold.
 * Grows heterotrophs and clinical isolates (facultative parasites) such as Streotococcus pyogenes.

Synthetic Media
Synthetic media are completely defined media in both quantity and chemistry. A mixture chemicals are added to a liquid or solid media to favor autotrophs, heterotrophs, hypotrophs, or even specific strains of organisms.

Amino acids are added as a source of organic nitrogen for heterotrophs, sugars are added as a source of energy, ammonium and potassium nitrate are added as an inorganic source of nitrogen for autotrophs, etc.

Synthetic media is chemically defined and sterile, but even fewer organisms will grow on the media. Also, synthetic media is extremely cost-prohibitive because of how expensive it is.

Classification by Use
All of the following media are complex.

Isolation Media
For example, a human pathogen can be grown on human, sheep or rabbit blood, but 5% sheep blood is most commonly used. An organism that grows in the sea would be grown with the help of sea salt, while an organism that originally lives in soil will be grown with the help of soil extract.

Differentiation Media
Differentiation media is used to detect enzyme reactions. A differentiation media will react and look different if a certain enzyme is present due to its contents, which often includes an indicator and a specific substrate.

Blood Agar Plate
A blood agar plate is a BHI plate with 5% sheep blood added, which tests for hemolysis, or the breakdown of blood.

Mannitol Salt Agar
The mannitol salt agar was specifically designed for Staphylococcus aureus, which is a unwanted but common bacteria in hospitals. The mannitol salt is made of two main components: Mannitol, an alcohol that staphylococcus breaks down into acid, and phenol red (also known as phenolsolfonphthalein, or PSP). When mannitol is broken down into acid, phenol red indicates it by turning yellow. The mannitol is the differential part of this media

MacConkey's Agar
MacConkey's agar is used for detecting coliforms, or gut flora such as Escherichia coli, by using lactose as a differential component. The acid from the breaking down of lactose reacts with natural red dye and turns the colony purple.



Eosin (pink) Methylene Blue Agar
Similar to MacConkey's Agar, EMB also uses lactose as the differential component. When lactose is fermented, the colony is dyed purple. When Escherichia coli is cultivated on EMB, it will have a green sheen.

Selective Media
Selective media contains ingredients that favor the growth of certain organism while inhibiting the growth of others.

Mannitol Salt Agar contains 7.5% salt, which favors Staphylococcus aureus

MacConkey's Agar contains bile, which inhibits Gram-positive bacteria while Gram-negative bacteria, especially coliforms like Escherichia coli, can grow well because they are protected by their outer membrane.

EMB contains dyes that inhibit the growth of Gram-positive bacteria.

Thayer-Martin selective agar contains antibacterials, which inhibits Gram-positive bacteria, Gram-negative bacilli, and yeasts.

The Lowenstein Jensen Medium contains malachite green, which inhibit the growth of Gram-positive bacteria.

Enriched Media
Enriched media is used to grow fastidious organisms, which are organisms that have a complex nutritional requirement. In other words, a fastidious organism will only grow when specific nutrients are included in its diet.

Blood Agar
Streptococcus pneumoniae does not grow well on plain BHI, but by adding blood to the medium, the medium becomes enriched and allows for the organism to grow.

Chocolate Agar
Chocolate agar is an enriched growth medium  used for isolation of pathogenic bacteria.  It is a variant of the bl ood agar, containing red  blood cells that have been l ysed by slowly heating them to 80 °C. Chocolate agar is used for growing fastidious  respiratory bacteria, such as  Haemophilus influenzae and  Neisseria meningitidis. This helps H. influenzae, which requires  growth factors such NAD  (factor V) and hemin  (factor X), which are inside red blood cells. Therefore, the cells need to be lysed for the bacteria, which is not hemolytic, to access the growth factors.

Thayer-Martin Selective Agar
A variant of chocolate agar which contains (VCN) vancomycin, which inhibits Gram-positibe bacteria, Colistin (polyxymin E), which inhibits Gram-negative bacilli, and Nystatin, which inhibits yeasts. The Thayer-Martin selective agar helps grow N. gonorrhoeae.

Lowenstein Jensen Medium
The Lowenstein Jensen Medium contains a spore stain "malachite green", which inhibits Gram-positive bacteria. It is made using a BHI and enriching it with eggs and potatoes, and is used to grow Mycobacterium tuberculosis.