Role of biofilms in the etiopathogenesis of chronic sinusitis

Introduction:

Management of chronic sinusitis is becoming difficult by the day. It is assuming importance because of its effect in the quality of one's life. Recent researches have started attaching lot of importance to the formation of biofilms in the nose and paranasal sinuses as the suspected cause for the chronicity and refractoriness of the infection.

Diagnostic criteria for chronic rhinosinusitis:

The following are the diagnostic criteria for chronic rhinosinusitis:

1. Symptoms lasting for more than 12 weeks

2. Objective findings on CT scan paranasal sinuses which include obstruction to the osteomeatal complex area, oedema of nasal mucosa, sinus mucosa.

3. Objective nasal endoscopy findings - oedematous nasal mucosa, discharge from sinus ostium, oedematous mucosa blocking the infundibular area.

What is a biofilm?

Biofilm is defined as a structured community of cells enclosed in a self produced polymeric matrix. The whole structure is adherent to a living or inert surface. The cell community could include bacteria & fungus. These cells communicate with one another in a cooperative manner.

The matrix is usually slime like, containing polysaccharides, nucleic acids and proteins.

Classic example of biofilm is the dental plaque.

A patient with chronic rhinosinusitis undergoes culture of nasal secretions to identify the causative organism and its susceptiblity to antibiotics. It should be borne in mind that in the presence of biofilm the causative organism is highly resistant to antibiotics even though culture sensitivity results suggests otherwise.

Formation of biofilm:

Formation of biofilm occurs initially as a random collection of independant free floating bacteria which attaches to the surface forming microcolonies. When the size of the colony reaches a critical point interbacterial cross talk starts to occur. This cross talk is known as "Quorum sensing". The process of quorum sensing initiates the process of protein expression which leads to the formation of biofilm. Generation of biofilm leads to formation of towers, layers and water channels. The exopolysaccharide matrix is formed from bacterial extrusion. Bacteria existing in the biofilm can evade the host's defence mechanisms. They are also not susceptible to antibiotics.

Biofilm also can release bacteria in planktonic forms predisposing to infection in other remote sites.

How the presence of biofilm increases bacterial resistance to antibiotics?

1. The presence of polysaccharide coat in the biofilm prevents complete penetration of antibiotics into the biofilm.

2. Antibiotics on reaching the insides of biofilm are deactivated when they interact with negatively charged polymers of the biofilm matrix.

3. Bacteria in the basal layers of biofilm are postulated to be present in an inactive state. Antibiotics dont act on non dividing microbes.

4. The pores in the cell wall of bacteria residing inside the biofilm are found to be tightly closed preventing entry of antibiotics into the cell of the organism. This closure occurs as a result of hypertonic environment present inside the biofilm.

Biofilms are supposed to be involved in:

1. Nosocomial infections

2. ICU pneumonias

3. Chronic rhinosinusitis

4. Catheter infections

5. Infections affecting a-v shunts

Stages of biofilm formation:

Stage I: Attachment of bacteria to the surface initiating a cascade of gene expression allowing the microbes to chemically communicate with each other

Stage II: Is characterised by tight adherence of bacteria to the mucosal surface

Stage III: This stage is characterised by formation of bacterial colonies

Stage IV: This stage is characterised by formation of mushroom shaped towers

Stage V: Is detachment of biofilm

Drugs if evolved which could prevent the formation of biofilm could go a long way in effectively managing chronic rhinosinusitis.