When culturing in glass, or using sharp needles around cultures, then the chance that you are poked or cut with cell-carrying items should be minimized, both to prevent virus spread and to prevent introduction of an immortalized cell into the body. Glass and plasticware should be sterile. Although the bags containing the plasticware can be maintained outside the hood, they should not be opened outside the hood. Medium, Antimicrobials, Supplements, Trypsin. There are MANY type of media available.
Different cells do better in specific types of medium.
The commercial media that is commonly used also contains a buffer to help maintain pH, and a pH indicating dye. If your medium goes from being light pink, to very bright pink, then not enough CO2 is present. Some researchers do not believe in adding these antimicrobials, as they could influence cell behavior. Glutamine is a vital nutrient, which is added prior to use because of its tendency to break down. Trypsin is used to break the bonds that the cells have formed with the plastic, so that the cells can be removed and split into new containers.