Prevotella melaninogenica
Beth Groenke

Prevotella melaninogenica are gram-negative, non-spore forming, obligate anaerobic, coccobacilli that are commonly found in the oral cavity of humans; however, they are also found in other areas of the body where they can act as opportunistic pathogens. These bacteria are also found in the rumen of cattle and sheep, where they aid in the breaking down of proteins and carbohydrates. Originally discovered in 1921 by Oliver and Wherry, Prevotella melaninogenica was re-classified from Bacteroides melaninogenicus, due to new information gathered from 16s rDNA sequencing, circa 2002. They are now classified as follows: Bacteria, Bacteroidetes, Bacteroidetes, Bacteroidales, Noctuoidea, Prevotella, Prevotella melaninogenica.

Tests performed on the bacteria reveal that they can hydrolyze esculin, but not starch, that they produce acid in peptone-yeast-glucose medium and in peptone-yeast-mannose medium, that they are catalase, indole, and lipase negative and that they are bile sensitive. P. melaninogenica  are very acidic as illustrated by their ability to liquefy gelatin and to clot milk. They will generate acetic, isobutyric and isovaleric acids. P. melaninogenica will not reduce urease or nitrogen, indicating that they may only receive nutrients from an organic donor. They are also one of a limited number of bacteria that can product collagenase, an exotoxin, which breaks the peptide bonds in collagen and allows pathogenesis of other bacteria. P. melaninogenica grows at an optimal temperature of 37°C, which is logical because that is also the average human body temperature. This bacteria is inhibited by the presence of iron; therefore, it thrives in areas of lower iron content, such as in cervicular fluid. It can, however, create hemolysin under iron-limiting conditions. From a research perspective, P. melaninogenica is useful for media testing and for quality control purposes, aside from research aiming to learn more about the bacteria itself.

P. melaninogenica has been associated with many types of infection including: oral abscesses, infections in the intestinal tract, the female genitalia tract, the upper and lower respiratory tracts and in the bone marrow. Pyomyositis (infection of the skeletal muscles) has also recently been associated with Prevotella melaninogenica. This microorganism has also been linked with infections caused by dog and cat bites. It causes infections by producing hydrogen sulfide, ammonia, and cytotoxic substances. This microbe will also inhibit phagocytosis and killing of other bacteria when the body attempts to remove the invaders. Furthermore, P. melaninogenica can cause the host immune’s system to generate substances with tissue destroying potential. To further irritate the body, these microbes can generate hemolysin; therefore, they can lyse erythrocytes. However, this bacteria can also lyse other important cells like mast cells, neutrophils and polymorphonuclear cells.

In addtion to causing infections, because Prevotella melaninogenica are nonmotile, they contribute to developing a biofilm, particularly on the teeth, that can lead to periodontitis - the progressive loss of bone and recession of the gingiva around the teeth, which can lead to tooth loss if left untreated.

Although Prevotella melaninogenica seems to be nothing more than a menace to mankind, new research has indicated that it may be helpful in detecting oral cancer. Researchers from the Forsyth Institute, the Dana-Farber Cancer Institute, and the Harvard School of Dental Medicine have found that counts of P. melaninogenica and two other microbes had diagnostic power in 80 percent of oral squamous cell carcinoma cases once they reached a particular threshold value. This is a significant breakthrough because oral cancer is very difficult to detect in its early stages, as it rarely has symptoms until it has progressed. There currently is also no standard, effective screening method for oral cancer aside from a yearly check up, of which relatively few individuals take advantage.

Prevotella melaninogenica forming jet-black pigmented colonies


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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