Nasal flora

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The human nose in a schematic side view: the nasal flora colonizes the nasal cavity

The nasal flora , more precisely the microbiome of the nose , is the entirety of all microorganisms such as bacteria and fungi ( microbiome ) that colonize the nasal cavity of a person and form a natural component of the organ flora . The nasal flora is part of the microbiome and makes a significant contribution to protecting the organ and the entire organism from pathogens . The nasal flora is connected to the pharynx and oral flora via the respiratory tract . The composition of the nasal flora can differ greatly between individuals of the same species. In addition, it can change over time in one and the same individual.

Organisms of the nasal flora usually live as commensals or mutuals in the nose and colonize them, but some can also cause diseases. There are also interactions between the microorganisms in the nose. Diseases such as inflammation of the nasal mucosa (chronic rhinosinusitis ) and polyposis, as well as other influences such as smoking , can significantly influence the composition of the nasal flora.

The nasal cavity as a living space

The nose with the nasal cavity is the first section of the respiratory tract through which the air passes

The nasal cavity is a hollow organ that is lined by the nasal mucous membrane and equipped with numerous mucus-producing glands. The left and right nasal cavities are separated by the nasal septum ( nasal septum) and each divided into a nasal vestibule located inside the outer nose (vestibulum nasi) and the deeper nasal cavity proper (cavum nasi proprium) . The nasal cavity, which is lined with ciliated epithelium by the nasal mucosa, is subdivided into the three nasal passages (meatus nasi) in layers by bony-supported turbinates (Conchae nasales) between the floor and roof of the nasal cavity . Via the nasal vestibule and the nostrils , the nasal cavity has a connection to the outside world and the nasopharynx (nasopharynx) it is connected to the throat (the pharynx) and the oral cavity as well as the eustachian tube with the tympanic cavity in the middle ear , respectively. There are also connections to the frontal and sphenoid sinuses .

As part of the respiratory tract , the inside of the nose is one of the air-conducting organs, so it is constantly flowed through by the breathing air and represents the first area that it passes in the human body. Every day around 10,000 liters of air with all the microorganisms and impurities it contains are passed through the nose, some of which is cleaned here and its composition influences the nasal flora accordingly. Other factors in the nose are the high levels of moisture in the mucous membranes, the higher temperature than the outside world and the availability of nutrients. The pH value is largely stable and, at 5.5 to 6.5, is in the slightly acidic range; in the case of rhinitis it increases to 7.2 to 8.3. When nasal sprays or other pH-changing substances are applied, it usually buffers to a range between 6.2 and 8.0.

Examination of the nasal flora

Both cultivable bacteria ( culturome ) and microbial hereditary information that can be detected purely by molecular genetics on the 16S rDNA ( metagenome ) and RNA ( metatranscriptome ) level can be determined using modern examination methods. In some cases, novel identification methods such as the T-RFLP are used. However, scientific studies of the nasal flora are usually limited to the microbial colonization of the human nasal cavity, while studies of the nasal flora of other vertebrates are only available to a limited extent and are limited to human farm animals such as domestic pigs or domestic horses .

The colonization with pathogenic , i.e. disease-causing, microorganisms is of particular interest . In the case of the nasal flora of humans, the colonization with the pathogenic bacterium Staphylococcus aureus is the focus of research. It colonizes the mucous membranes of the nose and can cause serious infections, the antibiotic therapy of which is often made more difficult by the acquisition of multiple resistances (methicillin-resistant S. aureus , MRSA).

Composition and variance

The composition of the nasal flora is individual and varies greatly between different people; it can also be very variable in a single person over time. The population density is highest among small children and young people and decreases among older people. The nasal flora as well as parts of the skin flora , the flora of the hair and the flora of the auditory canal show the greatest variability in individuals over time compared to other body regions and in comparison between different people it is comparable in variability with the intestinal flora . A genetic influence on the individual nasal flora could not be determined so far and even in identical twins significant differences in the colonization of the nose were identified in a corresponding study , while only about 26 percent of the colonization matched. It is accordingly assumed that the individual composition of the nasal flora depends very strongly on the environmental conditions of the individual and is shaped both by the first colonization in infancy and as a result of various environmental influences. It was also found that the individual nasal flora is also independent of diseases such as chronic rhinitis and is therefore actually individually different and specific.

Core composition

The colonization of the nose consists of different types of bacteria: Some of them belong to a core composition, some of them are obligatory. The bacteria are usually commensals , but can also be opportunistically pathogenic. Based on various studies, typical communities could be identified as “core communities”.

Impurities and obligatory colonizers

Especially in the nasal cavity, which is in direct contact with the outside air and through which a constant stream of breath flows, there is also constant contamination and repopulation by microorganisms that live in the atmosphere or are associated with components of the air we breathe, such as house dust . House dust, for example, is mainly colonized by Gram-positive bacteria, including species of the genera Corynebacterium , Propionibacterium , Staphylococcus and Streptococcus , which represent a regular natural inoculation for the nasal cavity. At the same time, however, the people themselves are the main source of the bacterial composition of house dust and the environment. In addition to the air we breathe, hand-nose contact is a source of contamination of the nasal cavity, as numerous atypical microorganisms get into the nose from the hands can.

Medical relevance

The composition of the human nasal flora protects the nasal cavity from infections as long as it is intact. At the same time, it can harbor pathogenic germs which, under unfavorable conditions, can lead to serious infections.

Pathogenic germs

Staphylococcus aureus , a potentially pathogenic germ in the nasal flora
Streptococcus pneumoniae can cause various diseases

The nasal flora is of medical relevance for humans mainly due to the infection by the bacterium Staphylococcus aureus , which is a pathogenic germ responsible for a number of infections and for which the nose is the main place of settlement. As a rule, it colonizes the mucous membranes of the nose and is one of the regular, permanent and inconspicuous bacteria. It occurs in around 20 percent of all people and usually has no pathogenic effect; another 30 percent are occasional carriers of the bacterium. As a potential and opportunistic pathogen, S. aureus can also cause serious infections, the antibiotic therapy of which is often made more difficult by the acquisition of multiple resistances (methicillin-resistant S. aureus , MRSA).

Also, Staphylococcus epidermidis , which can be detected in all regions of the skin and in the nose, can be pathogenic facultative and after operations in immunocompromised people nosocomial infections trigger.

Another potentially pathogenic bacterium found in the nasal flora is Streptococcus pneumoniae , also known as pneumococci. Pneumococcus can cause various diseases, including in particular a lung infection (pneumonia), which can be fatal in children and the elderly. Other potential diseases are meningitis (meningitis), middle ear infection (otitis media), sinus infection (sinusitis) and inflammation of the cornea (ulcus serpens).

A connection between the colonization of the nose and the disease of chronic rhinitis, both with and without nasal polyps , does not seem to exist. The potential role of the nasal flora in these diseases is unknown.

Influence of diseases and disorders

Some diseases, such as asthma , can have a strong influence on the composition of the nasal flora. Living conditions and habits, especially smoking , also change the composition of the nasal flora and the pharynx flora, sometimes very significantly.

supporting documents

  1. ↑ a b c d e f g Melissa L. Wos-Oxley, Iris Plumeier, Christof von Eiff, Stefan Taudien, Matthias Platzer, Ramiro Vilchez-Vargas, Karsten Becker, Dietmar H. Pieper: A poke into the diversity and associations within human anterior nare microbial communities. The ISME Journal 4, 2010; Pp. 839-851. doi : 10.1038 / ismej.2010.15 , full text .
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