By Levi Clancy for Student Reader on
There are two types of tissue cultures: primary cultures, derived directly from animal tissues; and transformed cell lines, which are engineered to reproduce indefinitely.
Tissues cultures must be handled in biosafety hoods because they are innately considered biohazards (transformed cell lines are oncogenic), and are highly susceptible to the fungi which heavily populate breathing air.
A primary culture is harvested directly from animal tissue and then incubated in a tissue culture dish with nutrient-rich growth media enriched with blood serum. Primary cultures will frequently divide a limited number of times (due to their inherent programming) and also might contain different cell types.
Transformed Cell Line
A transformed cell line can divide indefinitely in vitro. Transformed cell lines are frequently derived from single cells, thus ensuring a culture with uniform genetic composition, growth characteristics and susceptibility to infection. Transformed cell lines are often derived from: tumors; primary cultures transformed or transfected to express oncogenes; from tissues treated with carcinogens; or from primary cultures with spontaneous oncogene mutations.
Tissue cultures are very susceptible to bacterial and eukaryotic contamination. For this reason, bacterial antibiotics are frequently added to their growth medium. In addition, media changes pH as its nutrients are consumed and cell waste accumulates. CO2 is often kept at ∼5% in tissue culture incubators to help stabilize pH; also, a pH indicator is frequently added so that researchers know when to replace the media. Lastly, humidity is very important for tissue culture incubation so that the media does not evaporate.