Bacteria and fungi are grown on or in microbiological media of various types. The medium that is used to culture the microorganism depends on the microorganism that one is trying to isolate or identify. Different nutrients may be added to the medium, making it higher in protein or in sugar. Various pH indicators are often added for differentiation of microbes based on their biochemical reactions: the indicators may turn one color when slightly acidic, another color when slightly basic. Other added ingredients may be growth factors, NaCl, and pH buffers which keep the medium from straying too far from neutral as the microbes metabolize.
In this exercise, your table will make all-purpose media called nutrient broth and nutrient agar. These 2 media----one a liquid and the other a solid---are the exact same formula save for the addition of agar agar (really---agar agar), an extract from the cell walls of red algae. This particular medium will grow MOST bacteria that we use in lab: however, it is classified as a rather minimal medium since there is no added sugar to it (like trypticase soy agar or plate count agar).
The old way to make media was by the cookbook method----adding every ingredient bit by bit. The only time that is done today is when making a special medium to grow a certain finicky organism, where particular growth factors, nutrients, vitamins, and so on, have to be added in certain amounts. This medium is called a chemically defined medium (synthetic). Fortunately, the most common bacteria that we want to grow will do nicely with media that we commonly use in lab. Some of our media is bought, but most is produced in the prep area behind the lab. Since this type of medium has some unknown ingredients, or sometimes unknown quantities, it is called complex media.
It is really very simple to make complex media these days:
rehydrate the powder form of the medium
stir and possibly boil the medium to get the agar dissolved well
distribute the media into tubes
autoclave to sterilize the tube media
autoclave the agar medium for plate production and then pour into sterile petri dishes
In this exercise, your table will make all-purpose media called nutrient broth and nutrient agar. These 2 media----one a liquid and the other a solid---are the exact same formula save for the addition of agar agar (really---agar agar), an extract from the cell walls of red algae. This particular medium will grow MOST bacteria that we use in lab: however, it is classified as a rather minimal medium since there is no added sugar to it (like trypticase soy agar or plate count agar).
The old way to make media was by the cookbook method----adding every ingredient bit by bit. The only time that is done today is when making a special medium to grow a certain finicky organism, where particular growth factors, nutrients, vitamins, and so on, have to be added in certain amounts. This medium is called a chemically defined medium (synthetic). Fortunately, the most common bacteria that we want to grow will do nicely with media that we commonly use in lab. Some of our media is bought, but most is produced in the prep area behind the lab. Since this type of medium has some unknown ingredients, or sometimes unknown quantities, it is called complex media.
It is really very simple to make complex media these days:
rehydrate the powder form of the medium
stir and possibly boil the medium to get the agar dissolved well
distribute the media into tubes
autoclave to sterilize the tube media
autoclave the agar medium for plate production and then pour into sterile petri dishes
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