Aseptic operation

For a successful fermentation, it is vital that there should be no contamination of the culture. For this reason the entire fermenter, all ancillary equipment and the growth medium must be sterile before inoculation. The air supplied during the fermentation must be sterile and there must be no mechanical breaks in the fermenter which might allow microorganisms to enter.

All equipment is cleaned with hot water before use and then sterilized in situ with steam. The steam must be able to reach all parts of the fermeneter assembly so it is vital that the fermenter is designed to avoid pockets of air which may occur if valves are incorrectly sited. All the interior surfaces should be polished since rough surfaces can act as a reservoir for contaminating microorganisms.

The culture medium, which can be several thousand dm³, may be heat sterilized in the fermenter itself by passing steam through the cooling coils and jacket. Alternatively the medium may be prepared in a separate vessel and passed through a continuous sterilizer.

All additives, for example and antifoaming agent, must also sterilized, though strong acids or alkalis added to adjust the Ph do not need sterilization. The air supply to the culture medium is sterilized by filtration. Many types of filter materials have been developed to trap microorganisms. Filtration can remove bacteria and fungi but bacteriophages in the air cannot be removed this way and their presence could result in the loss of an entire culture. In some cases, therefore, the air is heated to inactivate any bacteriophages and then cooled again before it enters the vessel. A fermentation plant designed for the large-scale production of human growth hormone or of insulin, both rich sources of coliphages.

Why are bacteriophages a serious problem if they infect an industrial fermenter?

Air leaving the fermenter must be sterilized, particularly if recombinant organisms are being grown. Not only is this a safety requirement, but it also prevents key microbial strains from becoming available to competitor companies. Filtration is used to sterilize the air.

The point at which the agitator/impeller drive-shaft enters the vessel is a potential source of contamination, so double mechanical seals are used and the moving parts are lubricated with condensed steam to maintain sterility.

Explain the reasons for the following.

A A yogurt factory prepares fruit by sterilizing it and sealing it in large drums. The fruit is removed from the drum when required by pumping in sterile air.

B A supermarket has ultraviolet lights in its delicatessen area.

You are asked to design a new microbiology laboratory for a local hospital. Describe three structural features that you would include to promote microbiological safety in the new laboratory.

Дата добавления: 2015-11-16