The discovery of a new species of mouth bacteria may help scientists improve ways of fighting tooth decay and gum disease.

The bacteria, called Prevotella, are part of the normal microbial flora in humans and are also associated with various oral diseases and infections in other parts of the body.

"The healthy human mouth is home to a tremendous variety of microbes including viruses, fungi, protozoa and bacteria," said Professor William Wade from King's College London Dental Institute, in a news release.

“The bacteria are the most numerous: there are 100 million in every milliliter of saliva and more than 600 different species in the mouth. Around half of these have yet to be named and we are trying to describe and name the new species," he added.

Wade and his team studied healthy tissue as well as tumors in the mouth and found three strains of Prevotella that could not be identified. The researchers named the new species Prevotella histicola, which means 'inhabitant of tissue'.

"Interestingly, this species was isolated from within the oral tissues, both in oral cancers and normal, healthy tissue," said Wade. "This confirms other work showing that oral bacteria can invade both tissues and individual cells."

Tooth decay and gum disease are the most common bacterial diseases in humans, said Wade, and are caused by changes in the microbes normally present in the mouth.

The new research is published in the August issue of the International Journal of Systematic and Evolutionary Microbiology.