The “mobile microbiome”: journey beyond the mouth

An article¹ published in the Journal of Dental Research (JDR) reviews the latest contributions to dentistry’s understanding of the “oral health, total health” concept. We asked Dr. Christopher McCulloch, professor and director of the Matrix Dynamics Group at the University of Toronto’s faculty of dentistry, for his perspectives on the paper.

JCDA: This JDR paper reviews the oral bacterial species that have been implicated in a variety of systemic infections and inflammation such as atherosclerotic disease, adverse pregnancy outcomes, rheumatoid arthritis, inflammatory bowel disease and colorectal cancer, respiratory tract infections, and other organ inflammation and abscesses.

How strong is the evidence that a “mobile microbiome” can affect systemic health?

CM: Based on the evidence, the authors suggest that several conclusions can be drawn in which they emphasize the relative strength and weaknesses of the associations and the need for careful consideration of the data. In particular, since the experimental design of the reviewed studies does not permit a clear-cut, cause-effect relationship to be established, and since the fundamental pathogenesis of these diseases are themselves not fully defined, it will be important that responsible interpretations of these relationships is considered. What I mean by this is that we should NOT over-interpret the connections and try to tell patients that their oral microbiota are directly implicated in these diseases. I believe that this would be irresponsible and possibly fool-hardy.

JCDA: Do the authors shed any new light on how oral bacteria, regardless of their pathogenic potential in the mouth, become pathogenic in other parts of the body?

CM: The authors note that, “oral bacteria have developed aggressive mechanisms to invade and persist in the host cells, to escape host immune surveillance, to adapt to niches at extra-oral sites, and to induce inflammatory responses leading to adverse systemic effects.” These are worthwhile generalizations and seem to be particularly important for several types of subgingival organisms that can reside in intracellular vacuolar compartments of host cells for long periods, but without causing cell death. For example, the potential persistence of certain species of oral bacteria in crevicular epithelium of periodontal pockets may provide a protected niche which confers protection on the bacteria. When conditions are “right” for the bacteria, conceivably these persistence mechanisms could facilitate their more rapid re-colonization of deeper periodontal tissues.

JCDA: What are the authors’ main conclusions?

CM: There are 3 main conclusions:

1. It is possible that periodontal infections may cause bacteremias. While there is a lot of controversy about the pathological significance of orally-derived bacteremias and their contributions to systemic dissemination, this idea certainly provides an opportunity by which oral bacteria could contribute to pathological alterations of remote sites, such as a cardiac valve that exhibits non-laminar flow. This notion underlines the importance of good oral hygiene to reduce overall bacterial load and bacterial dissemination.
2. There is a need to develop more accurate and more readily used bacterial detection techniques for effective patient management and accurate identification of individuals with virulent bacterial subtypes.
3. Current data relating oral bacteria to extra-oral infections is of an associative nature. Mechanistic studies with much stronger experimental designs (i.e. ability to establish cause-effect) are needed to discover a potential role of oral bacteria in systemic health.

-Adapted from an Oasis Discussions blog post. Join the discussion at: www.oasisdiscussions.ca/2013/07/05/mic/