The Paranasal Microbiome in Chronic Rhinosinusitis

In an article published in Otolaryngologic Clinics of North America, Thad Vickery and Vijay R. Ramakrishnan, MD, from the University of Colorado School of Medicine, Aurora, discuss chronic rhinosinusitis (CRS), with a focus on host-microbe interactions that contribute to its formation.

CRS is a common, chronic inflammatory disorder of the paranasal sinuses and is one of the most common healthcare problems in the United States. According to the authors, “CRS is characterized by persistent inflammation, a dysregulated immune response, and host-microbial interactions that together result in disruption of epithelial barrier function, poor wound healing, tissue remodeling, and clinical symptoms.”

CRS is currently recognized to be an inflammatory condition rather than an infectious one. The idea of a host interacting with just one pathogen during CRS formation has now shifted toward the concept of involvement of a more complex combination of relationships between communities of microbes and the host. Inflammatory processes that are modulated by commensal and pathogenic bacteria are now considered to contribute to CRS.

The microbiome is the collection of commensal, symbiotic, and pathogenic microorganisms that exists in a microenvironment in the body. And while research into the microbiome has largely focused on the gastrointestinal tract, understanding of a complex human-microbial community relationship in the paranasal sinuses has also grown in recent years. Indeed, the sinuses are not sterile, and a microbial community in this region probably contributes to maintaining the sinonasal mucosa in a healthy state, whereas disruption of this microbial population might contribute to inflammation through various mechanisms.

The types of bacteria in the paranasal microbiome that either protect against CRS, or cause it, remain unknown. However, studies have identified certain patterns. In particular, Propionibacterium acnes, Staphylococcus epidermidis, S. aureus, and Corynebacterium species have been commonly identified in healthy individuals. Similarly, although hundreds of bacterial species have been identified in CRS, the abundance of pathogenic bacteria is increased in patients with CRS, and anaerobic organisms and S. aureus have been identified more frequently in these cases than in healthy individuals. However, studies have revealed that bacteria are present in approximately equal quantities in health and in CRS. Research has also shown that CRS is associated with decreased bacterial diversity, which is similar to the situation in other disease states—for example, a less diverse gut microbiome is associated with obesity, inflammatory bowel disease, and psoriatic arthritis.

Despite accumulating evidence that diverse microbial communities are important for maintaining human health, the authors note that current CRS therapy is nonspecific, and that use of broad-spectrum antibiotics eradicates large groups of commensal as well as pathogenic bacteria. However, while interest in using probiotics and prebiotics to restore healthy microbial community function in the gastrointestinal tract has increased, data from clinical trials involving these products for nasal health are still lacking.

Although Vickery and Dr. Ramakrishnan acknowledge that bacterial microbiome research is still an emerging field, they emphasize that it is one of the most intriguing current topics of CRS research.

“Further studies directed at characterizing the entire microbiome population in health are necessary in order to develop a more robust understanding of the role microbial diversity plays in sinonasal health as well as the generation of disease,” the authors concluded.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.