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Prevotella species are a part of the oral flora.Prevotella nigrescens (P. nigrescens), a member of this family, was first discovered in within a group of bacteria termed Bacteroides intermedius. Following this discovery, P. intermedia and P. nigrescens were found to play a role in the pathogenesis of periodontal and endodontic disease. More recently, P. nigrescens was also found to be associated with signs of carotid atherosclerosis even in patients without periodontitis.
As more information on the pathogenesis properties of P. nigrescens was uncovered, there was a demand to find a treatment. Under this pressure a potential alternative treatment, to antibiotics, for P. nigrescens was found in the use of bee glue.

Cellular morphology and biochemistry

P. nigrescens are black-pigmented bacteroides that ferment carbohydrates. They are gram-negative, non-sporing, obligatory anaerobic, rod-shaped bacterium of the genus Prevotella that is commonly found in oral flora.
Differentiating between P. nigrescens and its sister bacterium P. intermedia, high stringency conditions (70C) revealed that P. nigrescens had different hybridization levels with the strain ATCC 25611 than did P. intermedia. Further characterization revealed that P. nigrescens also had electrophoretic mobilities that were faster.
Cells grow in broth cultures are 0.3 to 0.7 µm wide by 1 to 2 µm. In agar, colonies are 0.5 to 2 mm in diameter, circular, low convex and smooth. In blood agar, the cells are brown to black suggesting weakly hemolytic, and sometimes alpha-hemolytic, properties.
P. nigrescens uses mixed fermentation in anaerobic living conditions, breaking down dextrin, glucose, maltose, and sucrose. In the process of fermentation, they produce acetic, isobutryic, isovaleric, and succinic acids. The principal respiratory quinones are unsaturated menaquinones. The G+C content of the DNA is 40 to 44 mol%.

Differentiation from P. intermedia

Identification of samples as either P. intermedia or P. nigrescens can be made based on differences in malate and glutamate dehydrogenase electrophoretic mobility. SDS-PAGE of whole cell samples show that P. nigrescens have 31 and 38 kDa proteins that are not present in P. intermedia. Surface biotinylation of cells revealed that the 31 kDa protein is on the surface of the protein. Fimbria-like projections were also observed in negatively stained cells of P. nigrescens but not in P. intermedia. Although no further research has been done on the 38 kDa protein, this protein may be of further help to distinguish both species as it stained strongly only in P. nigrescens.
In terms of enzymatic differences, P. intermedia contain fast-moving enzymes whereas P. nigrescens have slower moving enzymes. P. intermedia and P. nigrescens also differ in localization. P. nigrescens is almost three times more frequently isolated from infected root canals than P. intermedia.^[5]

Role in Disease

Periodontitis

P. nigrescens is part of the orange complex of subgingival and supragingival plaque. It is also strongly related to bacteria of the red complex, which is the most commonly used periodontal diagnosis and therefore is considered “periodontal pathogens”.
Recently, it was discovered that P. nigrescens is found more frequently in subgingival plaque of patients with periodontitis^[1]. Researchers found a correlation between increased colonization of P. nigrescens and periodontitis ^[1]. Another group found that up to 70% of patients with localized and generalized forms of onset periodontitis had detectable levels of P. nigrescens in their subgingival plaque._[9] More recently, P. nigrescens was accepted as a putative periodontal pathogen for periodontal disease. Studies suggest that the root of its pathogenicity lies in that it seems to promote the release of inflammatory mediators._{[10] [11]}

Treatment

The development of new therapies for treatment of oral cavity diseases is of great importance since the development of antibiotic resistance of certain microbes. One of these new treatments that have emerged is the use of propolis, more commonly known as bee glue. The biological activities of bee glue include antibacterial, antifungal, antiprotozoan, antiviral, antitumoral, immunomodulation, anti-inflammatory and other therapeutic properties._[12] It has been shown to be effective in treating gum infections due to P. nigrescens (citation). P. intermedia and P. nigrescens strains were found to be susceptible to penicillin G, erythromycin, meropenem, metronidazole and tetracycline with MIC90 of 0.06, 0.13, 2.0, 4.0 and 4.0ug/mL. Three ethanolic extract of propolis inhibited growth of 90% (MIC90) of P. intermedia and P. nigrescens at 128ug/mL.

References

1. Stingu C.S., Schaumann R., Jentsch H., Eschrich K., Brosteanu O., Rodloff A.C (2013). Association of periodontitis with increased colonization by Prevotella nigrescens. Journal of Investigative and Clinical Dentistry 4 (1): 20–25.
2. Yakob M., Söder B., Meurman J. H., Jogestrand T., Nowak J., Söder P.-Ö. (2011). Prevotella nigrescens and Porphyromonas gingivalis are associated with signs of carotid atherosclerosis in subjects with and without periodontitis. Journal of Periodontal Research 46 (6): 749–755.
3. Fukui K, Kato N, Kato H, Watanabe K, Tatematsu N (1999). Incidence of Prevotella intermedia and Prevotella nigrescens carriage among family members with subclinical periodontal disease. Journal of Clinical Microbiology 37 (10): 3141–5.
4. Fernández-Canigia L, Cejas D, Gutkind G, Radice M. (2015) Detection and genetic characterization of β-lactamases in Prevotella intermedia and Prevotella nigrescens isolated from oral cavity infections and peritonsillar abscesses. Anaerobe. 2015 Jan 23;33C:8-13.
5. Saheer E.G, Markus H, Haroun N.S, Anja K, Kari L, Michelle A. P., Deirdre A. D. (1994) Characterization of Prevotella intermedia and Prevotella nigrescens Isolates From Periodontic and Endodontic Infections. Journal of Periodontology 65(1): 56-61
6. Teanpaisan R, Douglas CW, Eley AR, Walsh TF (1996) Clonality of Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens isolated from periodontally diseased and healthy sites. Journal of Periodontal Research 31(6): 423-432
7. Kwang-Shik B, J. Craig B., Thomas R. S., Larry L. D. (2007) Occurrence of Prevotella nigrescens and Prevotella intermedia in infections of endodontic origin. Journal of Endodontics 23(10): 620-623
8. Shah HN, Gharbia SE (1992). Biochemical and chemical studies on strains designated Prevotella intermedia and proposal of a new pigmented species, Prevotella nigrescens sp. Nov. Int J Syst Bacteriol 42: 542–6.
9. Mullally BH, Dace B, Shelburne CE, Wolff LF, Coulter WA. (2000) Prevalence of periodontal pathogens in localized and generalized forms of early-onset periodontitis. J Periodontal Res 35: 232–41.
10. Kikkert R, Laine ML, Aarden LA, van Winkelhoff AJ (2007). Activation of toll-like receptors 2 and 4 by Gram negative periodontal bacteria. Oral Microbiol Immunol 22: 145–51.
11. Airila-Mansson S, Soder B, Kari K, Meurman JH (2006). Influence of combinations of bacteria on the levels of prostaglandin E2, interleukin-1ß, and granulocyte elastase in gingival crevicular fluid and on the severity of periodontal disease. J Periodontol 77: 1025–31.
12. Santos, F. A., Bastos, E. M. A., Rodrigues, P. H., de Uzeda, M., de Carvalho, M. A. R., de Macedo Farias, L., Moreira, E. S. A. (2002). Susceptibility of Prevotella intermedia/Prevotella nigrescens (and Porphyromonas gingivalis) to propolis (bee glue) and other antimicrobial agents. Anaerobe, 8(1), 9-15.

Edited by Nancy Zhu, a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2014.