The microorganisms are classified according to the affinity/tolerance to oxygen, basically in the following groups:

• Aerobes: They show optimum growth in the atmosphere with oxygen tension similar to that of the air (approx. de 21%).
• Facultative anaerobes: they can grow indistinctly in atmospheres with different concentrations of oxygen.
• Microaerophiles only grow in atmospheres with oxygen tension that is lower than that of the air.
• Strict anaerobes: They cannot grow in the presence of oxygen.

The methods that are used to obtain the desired atmosphere in a culture range from the normal aeration (ambient air); until those that obtain an anaerobic atmosphere, which is completely devoid of oxygen  (anaerobic oven and anaerobic jars) in which the desired atmosphere can be obtained either through gas insufflation or by modifying the air using CO2 generators.

	Anaerobic jars The gas generation sachet GasPak EZ is a reagent sachet that contains inorganic carbonate, activated carbon, ascorbic acid and water.

Procedure

Inoculate two nutrient agar plates with a suspension of garden soil in a physiological saline solution.
Incubate one of them at 37ºC with normal aeration and the other one is put in the jar to incubate it in an anaerobic atmosphere at 37ºC.

37º with oxygen	37º without oxygen

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