These are Gram-negative, non-sporing non-acid fast bacilli. They are strict anaerobes and are generally nonhalophylic with a wide growth range depending on the group. Some will grow on most simple bacteriological media, while special nutrients are required by others. These may include vitamins, other cofactors and amino acids. Many metabolize peptones and amino acids. Some require fermentable carbohydrates. A variety of biochemical activities are noted in this family. Bacteroides is the type genus. The other genera include Porphyromonas, Fusobacterium, Leptotrichia and Selenomonas. Most of these include a wide variety of species. Based 16S RNA sequence homology studies, Selenomonas may be removed from this family. Motile with periprichous flagellae or non motile.

Genera

The Genera.

Bacteroides : There have been described a number of species, B. fragilis is the type species. The species are anaerobic, moderately saccharolytic and may or may not be pigmented. A wide variety of species are being described, which may have to be placed in other genera as a result of more extensive studies.

Porphyromonas:

Fusobacterium:

Leptotrichia:

Selenomonas: They are anaerobic curved or crescent-shaped rods, motile with a flagellar tuft giving them a characteristic tumbling motility. S. ruminantium is the type species.

Species Profiles

S. rumantium

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