Obligate anaerobes may use fermentation or anaerobic respiration. Aerotolerant organisms are strictly fermentative. In the presence of oxygen, facultative anaerobes use aerobic respiration; without oxygen, some of them ferment; some use anaerobic respiration.or practical purposes, there are three categories of anaerobe: 1  Obligate anaerobes, which are harmed by the presence of oxygen. 2  Aerotolerant organisms, which cannot use oxygen for growth, but tolerate its presence. 3  Facultative anaerobes, which can grow without oxygen but use oxygen if it is present.