What are the different types of culture media?

Culture media are mediums which supply essential nutrients and minerals to facilitate the growth of microorganisms. This media is used in microbiological tests to yield pure cultures, testing viable count, testing antibiotic sensitivity, determining efficacy of antimicrobial agents, and to separate microorganisms from a mixed population. 

Culture media can be classified based on their nutritional contents:

• Simple media (e.g. nutrient broth) promotes the growth of non-fastidious microorganisms and is mainly used for isolating microbes. 
• Complex media (e.g. Tryptic Soy Broth) contains nutrients with unknown quantities that promote specific attributes in microbial strains. 
• Synthetic media (e.g. Czapek Dox Medium) is composed of pure chemical substances; it is formulated with known concentration of ingredients and nitrogen sources. 

Culture media can be classified according to their consistency:

• Solid media (e.g. Chocolate agar) contain agar or other solidifying agents at concentrations around 1.5-2.0%, solidifying at 37 degrees celsius. They are used to grow microorganisms in full form, study colonies, and produce pure bacterial cultures. 
• Semisolid media (e.g. Amies Media) is used with lower agar concentrations (0.2-0.5%), and is a jelly-like substance. It is used for researching microbial motility and growing microaerophilic bacteria. 
• Liquid media (e.g. Phenol Red Carbohydrate Broth) does not use agar. They allow the abundant growth of bacterial colonies, appearing uniform after incubation at 37 degrees celsius for 24 hours. This media is used for extensive microbial growth and fermentation research. 

Culture media can be classified based on their application or media composition:

• Basal media is the basic media used for growing bacteria which do not require additional nutrients. Some examples of basal media are nutrient agar and nutrient broth. Bacteria such as Staphylococcus and Enterobacteriaceae are able to grow in these media. 
• Selective media is designed to promote the growth of specific bacteria by inhibiting the growth of undesired ones. Examples include MacConkey Agar; antibiotics may be also added to further inhibit unwanted bacteria. 
• Enriched media contain additional substances such as egg yolk, blood, or serum to the culture media. This media is used to grow microorganisms that require additional nutrients. Examples of this type of media include chocolate agar or blood agar.