Sterilisation by heat

Irradiation, e.g. 60Co y-irradiation is used commercially for disposable plastics Ethylene oxide treatment 

The last two methods are not generally applicable to the small laboratory except insofar as low pressure mercury vapour lamps emitting light of 254 nm may be used to sterilise the air in aseptic rooms and cabinets (see 9.4.1). 

This involves heating the glassware to 160°C for 90-120 min. It is the preferred method for bottles which do not have screw caps when their orifice should be covered with aluminium foil. It is also used for glass Petri dishes and pipettes. Petri dishes should either be stacked in tins or containers specially designed for them or simply held closed with sterilisation tape. This brown paper adhesive tape has pale strips which turn dark brown under sterilising conditions and is used as an indicator of the effectiveness of the procedure. It is available from the 3 M Company Ltd. (Appendix 3). 

Heat-stable solutions, rubber bungs and liners, bottles with plastic caps, ultrafiltration apparatus etc. are all sterilised by steam treatment at elevated pressure. Although the time required to sterilise is usually only about 15 min at 15 lb pressure the cycle time for modem autoclaves is several hours. This is because of the safety precautions built into these machines to prevent the doors being opened until the temperature of liquid within bottles has fallen to 80°C. 

To sterilise small items such as rubber bungs they should be placed in glass Petri dishes and wrapped in aluminium foil. 

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Desired properties. Innumerable compounds have local anaesthetic properties, but few are suitable for clinical use. Useful substances must be water-soluble, sterilisable by heat, have a rapid onset of effect, a duration of action appropriate to the operation to be performed, be nontoxic, both locally... 

According to the decision trees, where it is not possible to carry out terminal sterilisation by heating due to formulation instability, a decision should be made to utilise an alternative method of terminal sterilisation, filtration and/or aseptic processing. If this alternative route is taken, then a clear scientific justification for not using terminal heat sterilisation will be required in the NDA/MAA dossier. Commercial reasons will not be acceptable because terminal sterilisation offers the highest possible level of sterility assurance. 

Thermally stable material such as glassware or metal instruments may be sterilised by heating them in an oven at 185°C for two hours. The material is wrapped in autoclave paper prior to heating, and after removal remains sterile until the wrapping paper is removed. Steam treatment in an autoclave is normally used for the sterilisation of aqueous material. The autoclave uses steam at a pressure greater than atmospheric and laboratory systems normally operate at 15 lbs in which corresponds to a temperature of 121 °C. This makes the assumption that the atmosphere inside the autoclave is composed only of steam and therefore it is necessary to expel all the air before the sterilisation process commences. 

Both culture media must be sterilised by heating 20 min at 120° C in an autoclave. The Sabouraud medium is suitable especially for culture of fungi. In the preparation of the agar culture medium, 10 g meat extract and 1000 ml distilled water can be used instead of broth. 

Probably more than 50 % of the food eaten by people living in cities has been processed in some way or other. In general such people must take the foods provided by the food manufacturer, and the onus is initially on the food technologist to ensure the safety, wholesomeness and nutritive value of the foods. The consumer cannot assess such characteristics and he is completely in the hands of the manufacturer. Carelessness or ignorance can give rise to toxic hazards and to widespread poisoning within a community. As an example, some years ago a typhoid epidemic in Aberdeen was caused by an infected can of corned beef. After sterilisation by heat the can had been cooled in polluted water, which led to contamination of the contents by pathogenic bacteria. 

Tyrosine, tryptophan and tetracyline are filter-sterilised to prevent decomposition by heat sterilisation. 

Aseptic processing is used to achieve commercial sterility in a continuous flow of liquid or semi-liquid food by heating the food to a suitable temperature before placing it in previously sterilised packaging. The sterilisation of liquids containing particulates presents a number of... 

Dissolve phytomenadione in Solutol HS 15 heated to about 60 °C and add slowly the warm water. The sterilisation can be done by heat at 120 °C or by filtration. After the ampoules have been heat-sterilized, they should be shaken for a short time, while they are still hot, to eliminate any separation of the phases that may have occurred. 

Certain items, such as balanced salt solutions and versene which are heat-stable, are generally sterilised by autoclaving, but the majority of organic materials used in cell culture are filter-sterilised. For heat-sterilised materials it is generally sufficient to rely on a sterilisation indicator which should be included with each batch of materials being sterilised. Often autoclave tape is sufficient if used on each packet, but for solutions and larger containers, e.g. cans of pipettes, it is recommended that a liquid indicator is included within the bottle or can. 

To make the neutral red overlay medium first dissolve neutral red to 0.4% in distilled water (heat if necessary) and filter through Green s Filter Paper No. 904 (Appendix 3). Bottle in 20 ml amounts and sterilise by autoclaving at 15 lb pressure for 15 min. 

In peritoneal dialysis (PD), sterilisation of the fluid by heat leads to the presence of reactive carbonyl compounds, which have been incriminated in the progressive deterioration of the peritoneal membrane in long-term PD patients.441 Glutathione in conjunction with glyoxalase I, as well as aminoguanidine, counteracted the effect. 

The ampoules were filled with the CRM solution and left in contact with the solution for at least 24 h. After the conditioning each ampoule was emptied, filled with the solution and immediately heat-sealed. The samples were sterilised by gamma-irradiation with a °Co source, dose 25 kGy. After irradiation the ampoules were stored at ambient temperature in the dark. Some differences were observed in the contents before and after irradiation, particularly in the CRM 408 for hydronium, ammonium and nitrate. It was suspected that nitrate could have been formed from ammonium upon irradiation. Nitrite was also detected immediately after irradiation but was probably rapidly oxidised. 

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