Biomedical Engineering Reference
In-Depth Information
any other type of organism. Today, different types of algae are assigned to
plant and non-plant eukaryotic classes. Three classes of algae are now
assigned to Class Archaeplastida: Class Rhodophyta (red algae), Class
Chlorophyta (green algae) and Class Glaucophyta [73]. The golden and
brown algae are currently assigned to Class Heterokontophyta (Chapter 21),
as are the diatomaceous algae. Because the term “algae” applies to organ-
isms belonging to widely divergent biologic classes, it has lost much of its
taxonomic relevance.
Archaeplastida
Viridiplantae
Chlorophyta
Trebouxiophyceae
Chlorellales
Chlorellaceae
*Prototheca
Although every member of Class Archaeplastida descended from a cell that
contained a chloroplast, some of the descendants have lost the ability to
photosynthesize. Genus Prototheca is a chloroplast-free subclass of Class
Archaeplastida.
Prototheca species are unicellular algae ubiquitous in sewage and soil.
Presumably, all humans are exposed to Prototheca sometime in their lives, but
the number of human clinical infections is exceedingly rare. Protothecosis can
occur in any of three clinical forms: cutaneous nodules, olecrenon (elbow)
bursitis, and disseminated [87]. The two localized forms of protothecosis
occur in either immune-competent or immune-compromised individuals, while
the disseminated form seems to occur exclusively in immune-compromised
individuals. Only about 100 cases were reported by 2004 [88].
Cutaneous protothecosis is characterized by nodules. Histologic examin-
ation usually shows chronic inflammation (lymphocytes and histiocytes dom-
inating), and structures having the appearance of florets (i.e., resembling
flowers). These structures are produced by the organism's thick wall, known
as the theca (the “theca” of “prototheca”), within which are several auto-
spores that formed by cleavage of the large organism [87]. Budding is not
present.
Most human cases of protothecosis are caused by
Prototheca wickerha-
mii
, a species that causes disease in dogs, has been sus-
pected to cause some cases of human disease.
Infectious species:
.
Prototheca zopfii
Prototheca wickerhamii
(protothecosis)
