Biomedical Engineering Reference
In-Depth Information
Chlamydiae (Chapter 13)
Actinobacteria (Chapter 14)
The two phyla, Bacteroidetes plus Fusobacteria, are grouped in the same
chapter here, because they were both formerly assigned to the same (now obso-
lete) class, Saprospirae, the gliding, fermenting bacteria [50]. Fermentation is a
metabolic process wherein organic molecules yield energy. Bacterial gliding is
a process in which cells on a flat surface move through excreted slime (polysac-
charides). The process of gliding is different from the process of swimming,
and does not require flagella. Aside from organisms in Class Bacteroidetes and
Class Fusobacteria (Chapter 10), gliding is also seen in some members of Class
Gamma Proteobacteria (Chapter 7), particularly Class Pseudomonadales.
Bacteroidetes
Bacteroidales
Bacteroidaceae
*Bacteroides
Porphyromonadaceae
*Porphyromonas
Prevotellaceae
*Prevotella
Flavobacteria
Flavobacteriales
Flavobacteriaceae
*Elizabethkingia
Class Bacteroidetes has two major subdivisions, Class Bacteroidales and
Class Flavobacteria. The two divisions lack morphologic resemblance to one
another and are physiologically distinct (Class Bacteroidales is anaerobic,
Class Flavobacteria is aerobic). Nonetheless, their genotypes are similar, and
some species from either group produce sphingolipids, a chemical that is
seldom encountered in other eubacterial classes [21].
Members of Genus Bacteroides are mostly non-pathogenic commensals,
living in the human gastrointestinal tract; some are opportunistic pathogens.
Bacteroides organisms account for much of the material that composes feces.
The high concentration of Bacteroides species in fecal matter is a reminder
that not all intestinal bacteria belong to Class Enterobacteriaceae (Gamma
Proteobacteria, Chapter 7).
Peritonitis may occur when Bacteroides species leak into the normally
sterile peritoneal cavity. Bacteroides fragilis causes the vast majority of
peritonitis cases in humans.
Members of Genus Porphyromonas live as commensals or as opportun-
istic pathogens in the human oral cavity. Porphyromonas gingivalis causes
a clinically aggressive gingivitis that can lead to acute necrotizing ulcerative
gingivitis (ANUG) or extend to the tissues of the mouth and face, a condition
known as noma or cancrum oris.
