Sterilization

Once a microbiological experiment has been completed the live organisms should be safely destroyed. Same, before an experiment starts all living cells present should be inactivated so which only the inoculum desired is present? This poses problems for the microbiologist particularly one working with pathogens, thermophiles or sporulating bacteria. The process of pasteurization will kill many common human bacterial pathogens without affecting the medium a great deal and so is there- fore used in food preparation. Moist heat in the form of steam or boiling will kill most vegetative cells as well as some viruses but thermophiles and endospores will survive. The Autoclaving contaminated equipment kills all cells as well as endospores but is not suitable for use with polycarbonate and will cause many carbohydrate medium components to caramelize. Various techniques have been used to deal with heat-sensitive components:

? Tyndallization – repetitive heating to 90–100∞C for 10 minutes followed through cooling for 1–2 days Allows endospores to germinate in the medium, that are then killed through the heating.

? Ultraviolet radiation – kills living cells but does not penetrate opaque containers or large volumes of solution well.

? g radiation – kills living cells but  causes brittleness in polypropylene and polycarbonate .

? Filtration of media – 0.22 mm filters can be suitable for aqueous solutions of heat-labile chemical constituents but it is difficult to filter large quantities efficiently that maintaining sterility.