Sterilizing filter microorganism

Taking this filtration analogy further, it should be technically feasible to sterile filter a liquid product and this is done when a product is said to be prepared aseptically. Here the solution is repeatedly filtered through filters considered to be absolute (that is, they remove all microorganisms) directly into presterilized containers and sealed in an atmosphere claimed to be clean since it too has been repeatedly filtered. Today the whole filling operation is often separated from the human operators by using so-called isolators. This type of operation is considered... 

The primary objective of a sterilizing filter is to remove microorganisms. The filter medium used to accomplish such an efficient retention may be classified as one of two types—the reusable type or the disposable type. 

Solutions or liquids can be sterilized by filtration through a sterile filter of nominal pore size of 0.22 micron (or less), or with at least the equivalent microorganism-retaining properties, into a previously sterilized container. 

The properties of flat-sheet filters may be defined (Section 11.4.1) by a nominal cutoff expressed in ftm. It is also possible to determine the maximnm quantity of microorganisms in suspension likely to be retained per cm of filter surface under specified operating conditions. Bacteria are mnch less efficiently trapped than yeast cells. The flow rate of the finest sterilizing filter sheets is naturally lower than that of clarifying sheets and they are also more snsceptible to clogging. 

Foaming is often present in aerated bioreactors. It is undesired, because it removes the cells and the cultivation medium from the reactor and blocks the sterile filter. However, it can be used for the recovery of proteins and microorganisms from the cultivation medium. 

To prevent contamination with undesirable microorganisms, the fermentor and auxiUary equipment must be sterilized before inoculation. This is achieved by steam, ie, at least 20 min at 121°C. The incoming air is filtered. 

Filtered air may be used to purge a complete room, or it m be confined to a specific area and incorporate the principle of laminar flow, which permits operations to be carried out in a gentle current of sterile air. The direction of the airflow may be horizontal or vertical, depending upon the type of equipment being nsed, the type of operation and the material being handled. It is important that there is no obstruction between the air supply and the exposed product, since this may resnlt in the deflection of microorganisms or particulate matter fiom a non-sterile surface and canse contamination. Airflow gauges are essential to monitor that the correct flow rate is obtained in laminar flow units and in complete suites to ensure that a positive pressure fiom clean to less clean areas is always maintained. 

Membrane filtration is the technique reeommended by most pharmacopoeias and involves filtration of fluids through a sterile membrane filter (pore size = 0.45 im), any microorganism present being retained on the surfaee of the filter. After washing in situ, the filter is divided aseptically and portions transferred to suitable culture media which are then incubated at the appropriate temperature for the required period of time. Water-soluble solids can be dissolved in a suitable diluent and processed in this way. 

The USP also recommends the use of biological indicators, whenever possible, to monitor all sterilization methods except sterile filtration. Biological indicators are generally of two types. If a product to be sterilized is a liquid, microorganisms are added directly to carefully identified representative samples of the product. When this is not practical, as with solids or equipment to be sterilized, the culture is added to strips of filter paper. The organism chosen varies with the method of sterilization. 

Groundwater. In Florida groundwater, aldicarb was converted to aldicarb sulfoxide under aerobic conditions. Conversely, under anaerobic conditions (pH 7.7), oxidative metabolites (aldicarb sulfoxide and aldicarb sulfone) reverted back to the parent compound (aldicarb). Half-lives in unfiltered and filtered groundwater were 635 and 62 d, respectively (Miles and Delfino, 1985). In sterile anaerobic groundwater at pH 8.2, aldicarb slowly hydrolyzed to the aldicarb oxime. In a microorganism-enriched groundwater at pH 6.8, aldicarb rapidly degraded to... 

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