What are the Methods of sterilization of the glass, devices and microbiological media
In microbiological cultivation the unconditional purity is required for all media. Substrates have to be free from undesirable microorganisms. This is achieved by sterilization. Sterilization is usually a thermal process, which involves the removal of all forms of microorganisms, both vegetative and spore as well as viruses. Wet heat sterilization is the most often used technique in a laboratory. Objects made of glass such as Petri dishes are wrapped with paper and treated with heat in an oven chamber at 160 or 180 ° C for 2 or 1 hour, respectively. Microbiological media, water, pipette tips, are sterilized in autoclave, using a pressure of 1 atm and the steam temperature at 121 °C for 15-40 min, depending on the type and volume of the sterilized material.
Certain substances, especially those readily hydrolysable should not be exposed to such a high temperature. These include vitamins, urea, aminoacids and concentrated solutions of glucose. Solutions of these substances are subjected to a tyndallization conducted in Koch apparatus. Tyndallization is the process of pasteurization repeated in three consecutive days at a temperature of 100 °C for 30 min. The first pasteurization eliminates vegetative forms, the second – spores, and the third gives a guarantee of material sterility. For media consisting of components with high sensitivity to temperature sterilization is conducted by cold filtration. For that purpose a filter having a pore size smaller than the plurality of bacterial cells,
<0.1 µm is used.
For sterilizing large areas UV radiation is typically used.
Aseptic work with microorganisms
In addition to the sterilization of glass, apparatus and microbiological substrates during operation of the micro-organisms required to preserve sterility in the handling of biological material and avoid unwanted contamination. The activities before and after working with microorganisms require disinfection of laboratory tables using alcohol or other disinfectant (Meliseptol rapid). The following activities such as: pouring agar plates or agar slopes, striking a microbial cultures on agar plates, transferring the microorganisms to the flask of liquid medium, etc., require to work in the vicinity of the burner flame. Inoculating loops and a glass spreaders need to be heated in the flame.