The Genus Bacteroides


The genus Bacteroides has been described over 100 years and comprises a group of small nonmotile, nonsporing, Gram‐negative rods; they are obligate anaerobes and form a major part of the bacterial flora of the human intestinal tract. Poor circumscription of this group has led to the genus accumulating a large and diverse collection of species that only superficially resembles this description but could not be accommodated elsewhere. Based largely on chemotaxonomic and genetic criteria the genus was reclassified (Shah and Collins, 1989) to encompass the type species Bacteroides fragilis and members of the ‘B. fragilis group’. This more restricted definition, spurred on mainly by 16S rRNA (ribosomal ribonucleic acid), has encouraged more in‐depth analysis of the colonic flora and a large number of new species have been described. Full genomes of four species have been completed. Such studies are providing a better basis for elucidating the biological role of specific species within the intestinal tract and their involvement in a variety of physiological and cellular processes.

Keywords: bacteroides; systematics; identification; salient features; biology and pathogenicity

Figure 1.

A phylogenetic tree constructed using neighbour‐joining methods (Thompson et al., ; Van de Peer and De Wachter, ) based on 16S rRNA gene sequences (approximately 1300 bp) from Bacteroides sp. and other closely related genera. Numbers at the nodes indicate percentage bootstrap values of 1000 replicates. GenBank accession numbers for each sequence are given. The separation of Parabacteroides from Bacteroides sensu stricto is clearly shown.

Figure 2.

MALDI‐TOF mass spectral traces of three representative clinical isolates of Bacteroides fragilis isolated at different times. This species is particularly diverse; however, several conserved mass ions are present among isolates. The mass signals shown are considered to represent the same biomarker within the set analytical error margin of 0.08%.

Figure 3.

MALDI‐TOF mass spectral traces of three representative Bacteroides species, B. uniformis, B. vulgatus and B. thetaiotaomicron compared to B. fragilis, the type species of the genus. Despite the high degree of physiological compatibility between species, characteristic mass ions are evident in the spectrum of each.

Figure 4.

The deduced three‐dimensional crystal structure of the metalloproteinase encoded by bft. The α‐helices are shown in red, whereas the β‐sheets are in yellow with the arrow tip showing the direction. The blue strands indicate the turns, whereas the green strands depict the amino acid residues which, according to computer predictions, do not fold into secondary structures. Reproduced by permission of Edward Arnold (Publishers) Ltd, from Shah HN, Gharbia SE and Olsen I (2005) Bacteroides, Prevotella and Porphyromonas. In: Borriello AP, Murray PR and Funke G (eds), Topley & Wilson, 10th edn, vol. 2, chap. 75, pp. 1939, figure 75.4, London.



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Further Reading

Duerden BI and Drasar BS (1991) Anaerobes in Human Disease. London: Edward Arnold.

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Shah HN, Gharbia SE and Duerden BI (1998) The genera Porphyromonas, Prevotella and Bacteroides. In: Balows A and Duerden BI (eds) Topley Wilson's Microbiology and Microbial Infections, vol. 2, Systematic Bacteriology, 9th edn, vol. 58, pp. 1305–1330. London: Arnold.

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Shah, Haroun N, Jacinto, Rogério C, Ahmod, Nadia, Langham, Sally, Gharbia, Saheer E, Kallow, Wibke, and Welker, Martin(Dec 2008) The Genus Bacteroides. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000450.pub2]