Bacteriology of normal non-Inflamed sinuses and its significance

Attempts to recover organisms from non-inflamed tonsils were carried out for over seven decades. Some studies failed to find any microorganisms and others recovered them only in a portion of the cases. Only three studies identified bacteria in all sinus sample. 

Brook evaluated the microbiology of maxillary sinuses of 12 adults and found an average of 4 isolates/sinus  of aerobic and anaerobic bacteria. The predominant anaerobes were Prevotella  Fusobacterium ,and Peptostreptococcus spp., and Propionibactreium acnes. The most common aerobic bacteria were beta-hemolytic Streptococcoci, Staphylococcus aureus, Streptococcus pneumoniae, and Haemophillus parainfluenzae.

Ramakrishnanet al. collected middle meatus specimens from 28 individuals with no sinusitis. Bacterial colonization was assessed in these specimens using quantitative PCR and 16S rRNA pyrosequencing. All subjects were positive for bacterial colonization of the middle meatus. S. aureus, S. epidermidis and P. acnes were the most prevalent and abundant microorganisms detected. The authors found rich and diverse bacterial assemblages in all of the individuals, including opportunistic pathogens typically found in the nasopharynx.

Aurora et al. compared the microbiome and immune response from 30 patients with chronic rhino-sinusitis (CRS) and 12 healthy controls. The microbiome was analyzed by deep sequencing of the bacterial 16S and fungal 18S ribosomal RNA genes. Although quantitative increase in most bacterial and fungal species was observed in patients with CRS relative to controls, the microbiomes of patients with CRS were qualitatively similar to the controls. The predominate aerobic organisms were Cyanobacterium , Curtobacterium, and  Pseudomonas spp., and staphylococcus aureus. The commonest anaerobes were Propionbacterium, and Prevottela spp.

Patients with CRS had increased levels of the following cytokines: IL-4, IL-5, IL-8, and IL-13, along with increased levels of eosinophils and basophils in the lavage. Furthermore, peripheral blood leukocytes obtained from some patients with CRS responded to control lavage samples (ie, to commensals) to produce IL-5. In contrast, the same lavage sample evoked no IL-5 production in leukocytes from healthy controls. These results may explain why systemic steroid treatment provides relief for some patients with CRS.

Colonization of non-inflamed “normal “ sinus is possible because there is direct communication between the sinuses nasal cavity through the ostia which could enable organisms that reside in the nasopharynx to spread into the sinus. The presence of bacteria in the sinus can explain why following closure of the ostium, these organisms may become involved in the emerging inflammatory process.

The study by Aurora et al. that the host response or lack of response to the normal sinus flora may be key to the development of sinus inflammation. Modulation the sinus flora by topical antimicrobial and/or probiotic organisms that may interfere with the growth of pathogens may be used to prevent and treat sinus inflammation. Future studies that would explore these modalities are warranted. 

                                                      

                                                       CT of normal sinuses