Anaerobic Agar is used for cultivation of anaerobic microorganisms. Anaerobic bacteria are unable to use oxygen as a terminal electron acceptor. Casein peptone and soy peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Dextrose is the fermentable carbohydrate providing carbon and energy. Sodium thioglycollate and sodium formaldehyde sulfoxylate act as reducing agents generating a low oxidation reduction potential, thus securing good anaerobic conditions. Methylene blue acts as the redox indicator, the blue color indicating the presence of oxygen. The testing procedures can be carried out using standard Petri dishes or Brewers Anaerobic Agar Plates, both with the medium cooled to 45-50 ºC. The seeding of the sample (clinical or food) can be performed by surface inoculation or by pour plate method. Normally the sample should never be heated to destroy the vegetative forms of the aerobe, as the anaerobic non-spore formers will also be destroyed. Nevertheless, sometimes it could be useful to heat the sample when spore formers such as Clostridium are sought, except C. perfringens, which rarel y forms spores. When heating is indicated, warm the sample suspended in a liquid diluent (peptone water, buffering phosphate solution, etc.) to 70-80 ºC for 10 minutes. The plates of Anaerobic Agar can also be incubated in a normal atmosphere covering the surface of the plates with a Brewerlid. When growth is observed, open the plate and pick the desired colonies. Incubate longer if necessary. If the medium has not been prepared fresh before use, it is necessary to heat and remelt to expel the dissolved oxygen. Thioglycollate Medium (Cat. 1508) without Indicator is an excellent enrichment broth and, frequently using it previously, yields better results than direct seeding.
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