Bacteroides is a genus of gram-negative, obligate anaerobic bacteria. Bacteroides species are non-endospore-forming bacilli, and may be either motile or non-motile, depending on the species. The DNA base composition is 40-48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids. They also contain meso-diaminopimelic acid in their peptidoglycan layer. One of the most important clinically is Bacteroides fragilis. Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.