Most bacteria live naturally in bacterial communities called biofilms. A biofilm is a surface-associated bacterial community embedded in an extracellular matrix consisting of proteins, carbohydrates and extracellular DNA. Dental plaque is a typical example of a bacterial biofilm. Unlike many classical infectious diseases, caries is associated with the resident oral microbiota. A change in biofilm ecology due to factors such as more frequent sugar intake and/or lack of an mechanical plaque control leads to increased growth of the bacteria associated with caries development.
To prevent dental caries, there has been a long, ongoing search for agents to control dental biofilms. A major obstacle to be overcome is that when bacteria are growing in biofilms it requires up to 1000 times higher concentrations of an antibacterial agent to kill these bacteria compared to planktonic (free floating) bacteria. This partly explains the high in vitro antibacterial efficacy of many compounds that lack in vivo clinical efficacy against bacteria growing in biofilms on teeth. Living in a biofilm protects bacteria from antibacterials in several ways: by retarded and reduced penetration of the agent; by binding compounds to the extracellular matrix; by enzymatic breakdown; by reduced growth rate of the biofilm bacteria, and by expression of efflux pumps that enable active transport of the antibacterial compound, thereby avoiding intracellular toxic concentrations.
In light of the global increase in antimicrobial-resistant bacteria, it’s of concern that some antibacterials may contribute to selection for cross- and co-resistance to clinical relevant antibiotics.
Scheie AA, Rukke HV and Petersen FC. Are antibacterials necessary in caries prophylaxis? In Dental caries: The Disease and its Clinical Management 3rd edition, Wiley Blackwell, 2015.