Culture Media : used in the lab to cultivate microorganisms. This media is a mixture of materials that will supply the nutrients for the organisms to survive. This will provide the moisture and the pH needed for them to grow.

Two main types of media; COMPLEX MEDIA and CHEMICALLY DEFINED MEDIA/SYNTHETIC MEDIA. Chemically defined media are easier to make in the lab, the exact chemical composition is known as a result of this. Complex media is made up of complex organic materials which are nutrient rich.

When the ingredients are prepared in solution this is called the BROTH or LIQUID MEDIUM.

MEDIA TYPES:

• GENERAL MEDIA OR GENERAL PURPOSE MEDIA.

  This contains enough nutrients to support the non-fastidous microogranisms. (Nutrient Agar)

• ENRICHMENT MEDIA

Blood Agar/Chocolate Agar

Beta Heamolysis- This is the complete absorbance of the iron and the blood cells are completely lysed. This will show as a halo around the colonies that are present. An exmaple of the bacteria that can show this are S.pyogenes and Staph.aureus.

Alpha Heamolysis - This is the partial lysis of the blood cell, this when the ring group of the heme molecule is broken down. This will show as iron left behind and a greenish hue on the colonies.

Gamma Heamolysis- The blood cells do not lyse this means that the organism does not contain the enzyme haemolysin. The colonies have no change and the agar colour also does not change. An example being, Enteroccoccus faecalis.

Chocolate Agar

This isnt to check the ability of heamolysis in organisms but rather make other componenets of RBC avalible to organisms that would not be in the other blood agar medium. These will avaliable to fastidious organsisms such as Neissera.menigitidis, gonnorrhoeae, and Haemophilus.

• SELECTIVE MEDIA

  Only allows the growth of limited amount of media and microorganisms and supresses the growth of others. Useful for isolating organisms.

• DIFFERENTIAL MEDIA

Allows differentiation of organsims using the different abilities of the organsisms. Media is used to isolate from natural sources and differential at the same time.

MacConkey Agar Selective and Differential.

This is used to isolate gram negative lactose fermenting bacteria. The agar contains bile salts and crystal violet, this permits the growth of gram negative bactera. A positive reaction of this would show a high fermenting lactose by the appearance of pink colonies and halo around the colonies as well as crystalsations of the bile salts which are found in the agar.

A medium fermenting bacteria would show the pink colonies but not the halo of the percipitate of the bile crystals. A non-fermenting result would show a a transperant agar plate and the colonies would not turn pink.

TSI Triple Sugar Iron Agar

This is used to see whether bacteria contain the enzymes to ferment Sucrose, Lactose or Glucose. This can also be used to see the indication of whether these bacteria can produce gas as well. Some bacteria can also break down of the agar this will indicate that they cause the blackening of the medium. The medium itself contains iron as the nutrient source and sucrose, lactose and glucose. This is a slanted medium that stands.

If the reaction is K/A this indicates the sugar glucose has broken down as well.

An A/A reaction means that glucose and either one or both of the sugars have also broken down. If bubbles are present this means that these organisms are also gas producing.

The blackening of the medium can also indicare motility of the bacteria.

Hugh and Leifson Medium for oxidation/fermentation test (O/F)

These are also tube test which contain glucose and can indicate whether these are metabolised by the bacteria. A closed tube (closed to oxygen using oil) and open tube (open to oxygen) test is used. Oxidation will use the oxygen and if a colour change is seen this means that it can metabolise is in the presence of oxygen. If the bacteria can cause a colour change when in a closed tube setting this indicates that the bacteria can metabolise glucose under anerobic conditions as well. A pH indicator is also added to show if the production of acid occurs from the glucose reactions.