Bacteroides loescheii

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Higher Order Taxa

Domain: Bacteria

Phylum: Bacteroidetes

Class: Bacteroidetes

Order: Bacteroidales

Family: Bacteroidaceae/Prevotellaceae

Genus: Bacteroidales/Prevotella

Species Name:

Bacteroides loescheii/Prevotella loescheii

Description and significance

Bacteroides loescheii is a gram negative, rod shaped bacterium which is found in the human mouth. It is also nonmotile, an obligate anaerobe, and does not form spores. It was named after the American dental microbiologist Walter J. Loesche. When grown on blood agar, the colonies formed are round, convex and smooth. Cells are usually alone, in pairs or in short chains when viewed under a microscope. When incubated for longer than 48 hours, they produce a light brown pigment. This species is often found in people with oral diseases, such as gingivitis and periodontitis. The C+G of Bacteroides loescheii is 49 to 51 mol%.

Genus Classification Change

When originally discovered, Bacteroides loescheii was placed in the genus Bacteroides. Since then similar species such as B. melaninogenicus and B. oralis have been reexamined, and it was determined that they were different enough from other Bacteroides species to classify them in a new genus, Prevotella. The ability of these bacteria to live in our mouths is part of how they were separated from other Bacteroides species. B. loescheii was reclassified and renamed Prevotella loescheii.

Cell Metabolism

B. loescheii can ferment sugars to produce succinate and acetate, though they can also produce traces of lactate and formate. Some of the sugars B. loescheii can ferment are glucose, sucrose, D-fructose, D-(+)-maltose, inulin, lactose, D-(+)-mannose, D-(+)-Raffinose, starch, esculin, and cellobiose. The fact that this bacterium can use esculin and cellobiose is used to help differentiate B. loescheii from other similar species, such as B. melaninogenicus and B. denticola.


Like similar species found in the mouth, Bacteroides loescheii can lead to gingivitis and periodontitis, painful inflammation of the gums and tissues around the teeth. If left untreated, teeth can fall out. Treatment usually consists of a thorough dental cleaning and an antibacterial mouthwash.

It has also been reported that B. loescheii can cause subdural empyema, pockets that fill with fluid where the bacterium grow. These are treated by draining the pocket and administering antibiotics, made more difficult by some strains' resistance to the antibiotic metronidazole.

Effective Antibiotics

There are a few antibiotics which are effective against Bacteroides loescheii. Chloramphenicol, clindamycin, penicillin, and tetracycline are all effective and can be used to treat infections. Metronidazole has also been used, but cases have been reported of B. loescheii in which it is resistant to metronidazole.

Current Research

This microbe has an adhesin gene which is programmed to undergo a frame-shift. The mechanism for this seems to be similar to a feature of retroviruses, which experience frame-shifts much more often than most bacteria. Studying how and why this frame-shift occurs could help us understand more about genetics.

Cases have been found where patients develop subdural empyema caused by Bacteroides loescheii bacterium resistant to the antibiotic metronidazole. Studying how these bacterium infect people and how they have become resistant to metronidazole could help find ways to prevent and treat infections.


1)[ Holdeman, L. and Johnson, J. ““Description of Bacteroides loescheii sp. nov. and Emendation of the Descriptions of Bacteroides melaninogenicus (Oliver and Wherry) Roy and Kelly 1939 and Bacteroides denticola Shah and Collins 1981”. International Journal of Systemic and Evolutionary Microbiology”.

2)Shah, H. and Collins, D. ““Prevotella, a New Genus To Include Bacteroides melaninogenicus and Related Species Formerly Classified in the Genus Bacteroides”. International Journal of Systemic and Evolutionary Microbiology”.”]

3)Wu, C., Johnson, J., Moore, W., Moore, L. “”Emended Descriptions of Prevotella denticola, Prevotella loescheii, Prevotella veroralis, and Prevotella melaninogenica”. International Journal of Systemic and Evolutionary Microbiology”.”

4)Manch, J and London, J “”Expression of the Prevotella loescheii adhesin gene (plaA) is mediated by a programmed frameshifting hop”. American Society for Microbiology Journal of Bacteriology”.”

5)Sweeney, L., Dave, J., Chambers, P., and Heritage, J. ““Antibiotic resistance in general dental practice—a cause for concern?”. Journal of Antimicrobial Chemotherapy”.”

6)[ Page, R. and Eke, P. ""Case Definitions for Use in Population-Based Surveillance of Periodontitis". Center for Disease Control".]

7)Vyas, J. ""Empyema." National Institute of Health."

8)Fotek, P. ""Periodontitis." National Institute of Health."

Edited by Emma Cole, student of Rachel Larsen at the University of Southern Maine