It is incorrect to call protection of the desired culture sterile
technique because sterility means that no life is present. Harboring the
desired organisms while preventing the growth of others is aseptic
technique. Precautions in the laboratory can be relaxed somewhat to expedite
work output because occasional losses are not costly. A pilot plant that
very infrequently encounters contaminated runs is considered excellent,
but the economic loss of one full-size, production fermenter to contamination
is cause for alarm. This was not always the case, and the first large scale
antibiotics plants battled contamination while aseptic technique was perfected.
Infections by phage were particularly difficult to combat because the virus
particles are small enough to escape capture by the filters used to sterilize
the air provided to the fermenters. Phage attacks were overcome by switching
to resistant strains of the microorganisms.
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Production cultures derived from plant, animal, or insect cells grow on expensive medium that contains many more special nutrients than found in the media for antibiotics, vitamins, and other products with bulk markets. The organisms that make antibiotics, in particular, are relatively easy to cultivate because their products discourage the growth of other microorganisms. Cell cultures, in contrast, have no self-protection and cannot compete with hardy, rapidly-growing microorganisms that find the media delectable.
Although there are many alternative designs, roughly 85 per cent of the fermenters in the world resemble closely the traditional design. Much more about fermenter layout could be added to our computer exercise. Foam sensing and the delivery of antifoam agent were not shown. The header for inoculation and harvest, pH electrodes, feeding systems, and other appurtenances are important to biochemical engineers. Also of great interest is interfacing with computers to monitor and control fermenters. You can appreciate that the pipes, fittings, wires, and sensors of a fermenter constitute a complicated system in which many things can go wrong.
Typical bioprocessing is considered a batch operation even though air and antifoam are added during the run. Adding nutrients or precursor compounds during the run gives rise to a fed batch system. The fed batch fermentation has become highly popular because concentrations and conditions can be adjusted to maximize production.