<P> A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent . An obligate aerobe, by contrast, cannot make ATP in the absence of oxygen, and obligate anaerobes die in the presence of oxygen . </P> <P> Some examples of facultative anaerobic bacteria are Staphylococcus spp., Streptococcus spp., Escherichia coli, Salmonella, Listeria spp. and Shewanella oneidensis . Certain eukaryotes are also facultative anaerobes, including fungi such as Saccharomyces cerevisiae and many aquatic invertebrates such as Nereid (worm) polychaetes . </P>

An organism that cannot grow without oxygen is a(n)