Oral Biofilm: Smart Bacteria in Action

protecting tooth film

protecting tooth filmThere are two systems of bacteria that occupy the oral cavity: plankton and biofilm. The name plankton is a Greek word meaning “drifter”. Plankton bacteria essentially drift about the mouth in a current of saliva, catching nutrients as they flow by. Some species of oral plankton are capable of independent movement with the help of appendages or flagella that propel them through salivary flow. Plankton bacteria have a life span of 18 minutes to 48 hours and are easily destroyed by antimicrobial rinses such as Oravital CDLx, a sodium chlorite preparation. 

Oral biofilms are complex, interactive, spatially and functionally organised systems of multiple species of bacteria grouped together with the prime purpose of survival. Biofilms are protected from host defenses and antimicrobial agents by a matrix and by neutralising enzymes.

Biofilm formation is challenging. Bacteria and their targets both have a negative charge so repel each other. It is only when sufficient positive charges accumulated from saliva surround the microorganism that attachment is successful.

Many species of streptococci are known to form biofilm. These first colonists, often S. mutans, extend the invitation to select groups of species and facilitate the arrival of these microorganisms by building the matrix that holds the biofilm together. Some species are not able to attach to a surface on their own but can anchor themselves to the matrix or directly to earlier colonists. Biofilm structure is planned, genetically directed, and grows through a combination of recruitment and cell division.

 When a microorganism switches from plankton activity to biofilm growth, it undergoes a change in behaviour through lateral gene transfer. Bacteria living in a biofilm have significantly different properties from free-floating bacteria of the same species including changes in appearance and behaviour.

Attachment and biofilm formation is by invitation only and in a particular sequence. Bacteria are very “talkative”, both amongst themselves and with other species. The communication process, known as quorum sensing, is the production of signaling molecules (chemicals) informing other bacteria that an attachment has been acquired and this is an invitation to join the colony. Quorum sensing can control physiological activities, antibiotic biosynthesis and induction of virulence factors.

 As the colony builds, protective barriers of extracellular polymeric substance are put in place so that in the final stage the colony consists of 1/3 bacteria and 2/3 matrix. The matrix retains water, nutrients and enzymes within the biofilm. A major feature of the matrix is that it is both difficult to penetrate by antimicrobial agents and can repel most antibiotics through enzyme activity. For example, a biofilm with beta-lactamase properties can dissolve penicillin antibiotics as they penetrate the first layer.

 A significant advantage of using topical antibiotic rinse combinations as offered by the Oravital™ System is the enormously higher degree of penetration (on the order of 4000 times more effective than systemic antibiotics), in addition to immediate treatment onset. These rinses contain particles of antibiotic that can enter the biofilm and because of the concentration are not easily neutralised.

Initially, biofilm contributes to the normal development of our own defenses and the relationship is symbiotic. Bacteria work hard to downgrade their pro-inflammatory cytokine and to decrease inflammation.

 Disease is caused by an imbalance in the composition of the resident flora. Shifts in the balance allow minor but virulent components of the biofilm to become predominant. Since bacteria are held together by the matrix, this close proximity provides ideal conditions for genetic transfer and contamination of beneficial bacteria. Biofilms become less synergistic and more antagonistic with the most aggressive pathogens safely on the inside of a protective matrix.

Dental biofilms can contain more than 700 different bacterial species and the complexity of structure adds to the challenge of disease control and prevention. The mechanical removal of biofilm is essential but only partially effective. Re-organization of biofilms can be rapid especially if the initial attachment layer is not destroyed. The addition of antimicrobial chemicals to mechanical removal may sufficiently disturb the biofilm formation to prevent complete rebuilding initially.

Current research includes attempts to develop a unique method of controlling biofilms: preventing bacteria from intercommunicating. Scientists have analysed the chemicals bacteria use for interspecies and cross species communication, and are looking at ways of neutralising these pathways. Controlling communication pathways would be an excellent method of chemotherapeutic control of bacterial virulence and establishing a healthy relationship with the host (us).

 Although this is interesting research, currently Oravital antibiotic rinses are the most effective way of dealing with an oral biofilm infection.

Smart Bacteria in Action

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