BIOPHARMACEUTICAL MANUFACTURING - Risk Management Applications in Pharmaceutical and Biopharmaceutical Manufacturing - page 329

Stationary
Time
Figure 12.4 Cellular growth curve for microbial cells.
12.3.3 Fermentation/Cell Culture
12.3.3.1 Process Overview
Fermentation In biopharmaceutical manufacturing, the term “fermentation”
describes any process for the production of a product by the large-scale
cultivation of a microorganism (occurring with or without air). The growth
of microbial cultures can be divided into a number of stages as shown in
Figure 12.4.
Initially, the microbial cells of interest are inoculated into a selected growth
medium, a period during which growth does not appear to occur (adaptation phase
or lag phase). The next phase is characterized by a period where the growth rate
of cells gradually increases as the cells grow at a constant, maximum rate (log
or exponential phase). During this phase, the microbial cells take up nutrients
from the fermentation broth and release products, byproducts, and waste metabo-
lites. Eventually, the growth of cells ceases, or the number of new cells formed
equals that of others dying (stationary phase), owing to the continuously falling
concentrations of nutrients and/or a continuously increasing (accumulating) con-
centrations of toxic substances. Finally, after a further period of time, the viable
cell number declines and the cells die (death phase). It is important to keep the
cells in growth phase because if they are allowed to reach the lag or stationary
phase, the culture may cease or lag depending on the cell line and growth medium
used. Once acceptable microbial cell growth is achieved, that microbial culture
can be used to inoculate the production fermentor. Microbial fermentations typi-
cally do not require elaborate cell accumulation and expansion steps (as required
for mammalian cell culture processes) because of the short doubling time for the
microbes (e.g., 15-20 min for Escherichia coli in the laboratory).
Cell Culture Tissue/cell culture is the general term for the removal of cells,
tissues, or organs from an animal or plant and its subsequent placement into an
artificial environment conducive to growth. This environment usually consists of
a suitable glass or plastic culture vessel (e.g., shake flasks) containing a liquid or
semi-solid medium that supplies the nutrients essential for survival and growth.