We have sinuses in our heads which we ignore when healthy, but which are a cause of suffering during sinus infections. You may be surprised to learn that millions of all sorts of microbes, both good and harmful, normally live in our sinuses. These microbes are the sinus microbiome, and they play a role in whether we are healthy or not.
What are our sinuses?
When we talk about our sinuses, we are referring to the four pairs of paranasal sinuses that are a part of the upper respiratory tract. The air-filled sinuses are located near the nose, and drain into the nasal cavity. They are named according to the facial bone in which they are located – maxillary, frontal, sphenoid and ethmoid. The largest sinus cavities are about an inch across, and the others are much smaller.
Paranasal Sinuses: Credit
Respiratory mucosa line the sinuses, and this mucosa has cilia and secretes mucus. The cilia steadily beat at about 700 to 800 times per minute and so help to move mucous into the nasal cavity. The sinuses make the skull lighter, they provide a way of filtering, humidifying, and warming inhaled air, production of nitric oxide (which also helps with oxygen uptake), and they help defend the airway against pathogens.
Two of the sinuses are already present (ethmoidal and maxillary) at birth, but they are very small in size. The other two sinuses are absent, but then begin to form over the next few years. The sinuses enlarge as a person gets older, especially at puberty.
A variety of microbes live in our sinuses
Sinuses were once thought to be sterile, and a sinus infection was a sign that harmful bacteria or other microbes had invaded them. “Germs” were the enemy and the focus was on eliminating them, frequently with antibiotics.
With the recent development of new technologies such as genetic sequencing, scientists discovered a rich and diverse community of many species of microbes living in the sinuses. The many species of fungi, viruses, and bacteria that live in the sinuses is called the sinus microbiome or microbiota.
A surprising finding is that species that are considered beneficial, benign, and harmful (pathogenic) all live together in complex communities in the sinuses. In healthy individuals the species are in equilibrium, with potentially harmful species kept in check. The microbes interact with one another and with their host (that’s us!).
When something causes a disruption and imbalance in the sinus microbial community (e.g. from infection, allergies, or air pollution), it is called dysbiosis. Disruption of the resident microbes in the sinuses can result in an overgrowth of harmful bacteria and increase susceptibility to infection, as well as cause sinusitis symptoms. In chronic sinusitis there is an imbalanced sinus microbiome and inflammation of the mucous lining of the sinuses.
Similarities & differences in bacteria in healthy persons and those with sinusitis
- All studies find that there are some bacterial differences in the sinuses between healthy individuals and those with sinusitis, but what they are varies from study to study. It is clear that there is no one “healthy sinus microbiome”. The main findings are: 1) there is more diversity and richness of species in healthy persons, and 2) in sinusitis some bacterial species are increased, while some others are diminished or depleted.
- The total number of bacteria present (bacterial load) in sinuses is surprisingly alike in both healthy persons and those with chronic sinusitis. This means that every bit of space in the mucus is occupied, whether with harmful, harmless, or beneficial bacteria.
Oral microbiome: Credit
- Both healthy individuals and those with chronic sinusitis have many microbes in common. Examples of common genera (a biological classification between family and species) are Staphylococcus, Corynebacterium, Propionibacterium, and Peptoniphilus.
- Many species that are “opportunistic pathogens” (meaning they can become harmful if given the right conditions) are found in low levels in the microbiomes of healthy sinuses. These pathogens have the potential to cause disease if there is a disruption of the microbial community.
Many studies find that the species Staphylococcus aureus, Haemophilus influenzae, Moraxella catarrhalis, and Corynebacterium tuberculostearicum may become dominant in those with sinus infections.
- Some bacteria may be viewed as keystone bacteria or gatekeepers for health - present in tiny amounts, but important for a healthy sinus community. Lactobacillus sakei (in Lanto Sinus) is one such species.
- Harmful bacteria can cause biofilms that live on the mucosal lining of the sinuses. Biofilms are communities of bacteria sticking to one another and coated with a protective slime, and which can be resistant to antibiotics. However, research finds that both healthy persons and those with sinusitis have biofilms in the sinuses.
Viruses, fungi, and archaea in the sinus microbiome
The viruses found in the sinus microbiome have not been studied much, especially in healthy persons. Studies find that each person has a unique virus profile or virome. Some viruses appear to be stable components of a person’s microbial community, but other viruses are only seen at single time points.
Fungi are found in the sinuses of both healthy persons and those with chronic sinusitis. Which fungal species are found varies from study to study, and much is still unknown.
Archaea can also be detected in some people in the sinuses. They are single-celled organisms that lack cell nuclei. One recent study found that only 6 out of 70 persons (both healthy and with sinusitis) had archaea in the sinuses, and they were very low in numbers. But another study found methanogenic archaea (the only microorganisms able to produce methane) in a small number of chronic sinusitis patients. It is unclear what their role is in the sinuses, and why only some people have them.
A healthy sinus microbiome varies from person to person
One perplexing research finding over the years has been that bacterial species in healthy sinuses varied from person to person. Researchers are now starting to think that there might be a number of normal patterns in healthy sinuses, rather than just one healthy microbial pattern or composition. It also appears that subgroups of bacteria occur together in healthy sinuses.
The research suggests this may also be true in those with sinusitis. Studies find that chronic sinusitis sufferers have imbalanced bacterial communities, but which bacteria dominate vary from study to study. Some researchers suggest that there are subgroups of bacteria that occur together and this varies from person to person.
Some other factors also can influence the species found in the sinus microbiome. Besides illnesses and allergies, other known factors include a person’s age, smoking, frequent courses of antibiotics, asthma, and previous sinus surgery.
The sinus microbiome develops during childhood
Right after birth, microbes start assembling in the upper respiratory system. The infant picks up bacteria during its birth, so at first the infant’s nasal cavity microbiome resembles the maternal vaginal microbiome or skin microbiome (if a C-section delivery). This changes over time.
Within a few years, the differences in bacterial species in the upper respiratory tract of children are like those in adults. An interesting 2016 study (Santee et al) compared bacterial communities between healthy children and those that had a history of acute sinusitis over the course of one year. They compared the nasopharyngeal microbiome in the 2 groups, who were between the ages of 4 and 7. They found a total of 951 species among the 47 children, of which 308 species had some "depletion" among those children with a history of sinusitis, while one species was increased in "abundance".
The healthy sinus microbiome is an incredibly complex community of bacteria, viruses, and fungi. This community is disrupted in chronic sinusitis, resulting in an altered composition of microbes. However, the field is still in its infancy and there is much we still don’t know.
The medical field is now taking the sinus microbiome into account when thinking about medical treatments for sinusitis. The feeling among researchers is that probiotic formulations (such as Lanto Sinus) will be commonly used in the future to restore equilibrium to the sinuses of people needing it.
The future is exciting!