How to use Dehydrated Culture Media
Safe disposal of cultures
The DIN Standard 58956 part 41 and the recommendations of the German Health Authority2 give information on the desinfection of microbiological cultures and the cleaning or disposal of contaminated material. There are particular references to dealing with substances suspected of being contaminated with pathogenic microorganisms. According to these recommendations, heat treatment disinfection is particularly important before cleaning or disposal are carried out. A chemical disinfection should only be carried out in exceptional cases.
A thermic disinfection of cultures in disposable vessels, in particular plastic, can be simply and effectively carried out by autoclaving them (approx. 30 min at 121 °C) in plastic bags with a high melting point3. When the microorganisms have been killed, the plates or the plastic bags and their contents can be thrown away. If suitable incinerators are available, the cultures can also be killed and destroyed by burning. Cultures in reusable glass vessels (e.g. conical flasks, culture test tubes) must first be killed in the autoclave (approx. 30 min at 121 °C). Also slightly contaminated glass vessels or heat-stable equipment are firstly autoclaved (134 °C for about 20 min) or sterilized in a hot-air cabinet (180 °C for at least 30 min). Then the vessels and equipment can be cleaned. If necessary sterilization can then take place -- also with autoclaving or in a hot-air cabinet. Chemical disinfection is carried out with appropriate disinfectants. The active ingredients in chemical agents are usually only effective against vegetative microorganisms but not against bacteria spores. Certain bacteria and certain viruses are more resistant to certain active substances than other microorganisms. In chemical disinfection all objects must be thoroughly wetted with the disinfectant. Therefore adherent air bubbles must be removed. For an adequate cover of a culture medium with disinfectant in a Petri dish with a diameter of 9 cm, 10 ml of disinfectant are necessary. The disinfactant should be allowed to act for at least 6 hours (e.g. overnight).
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION: Microbiology - General Guidance for the detection of presumptive pathogenic Yersinia
1)DIN Deutsches Institut für Normung e.V.: Medizinisch-mikrobiologische Laboratorien. Anforderungen an die Entsorgung. -- DIN 58956, Teil 4.
2)Bundesgesundheitsamt: Durchführung der Sterilisation. -- Bundesgesundhbl. 22; 193-200 (1979).
Bundesgesundheitsamt: Durchführung der Desinfektion. -- Bundesgesundhbl., 23; 356-364 (1980).
Bundesgesundheitsamt: Anforderungen der Hygiene an die Abfallentsorgung. -- Bundesgesundhbl., 26; 24-25 (1983).
3)Spezial-Vernichtungsbeutel (special bags for disposal) der Firma C.A. Greiner & Söhne, 7440 Nürtingen, and Firma Sarstedt, 5223 Nümbrecht.