adj. describing an organism that is not restricted to one way of life. A facultative parasite can live either as a parasite or, in different conditions, as a nonparasite able to survive without a host. Compare obligate.
n. any organism, especially a microbe, that is able to live and grow in the absence of free oxygen. A facultative anaerobe is a microorganism that grows best in the presence of oxygen but is capable of some growth in its absence. An obligate anaerobe can grow only in the absence of free oxygen. Compare aerobe; microaerophilic.... anaerobe
(Haemobartonella) n. a genus of Gram-negative bacteria that are facultative intracellular parasites. They occur in the red blood cells and cells of the lymphatic system, spleen, liver, and kidneys and cause several infections in humans (see bartonellosis).... bartonella
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