Dental plaque biofilms: communities, conflict and control.

From the very beginning of the discipline of microbiology, the dogma has been to isolate bacteria in pure culture in order to be able to define their individual properties. This process also involved the use of conventional broth (planktonic) culture to prepare biomass and to determine the phenotype of particular species. This approach provided a sound foundation for contemporary investigations of classical infectious diseases. Recently, however, there has been a renaissance in our understanding of microbial behaviour in natural habitats, and a recognition that chronic diseases can have a complex aetiology. It is now accepted that, in nature, bacteria exist for the most part attached to a surface as a biofilm, often as a member of a polymicrobial community (or consortium) of interacting species. If biofilms were merely planktonic-like cells that had adhered to a surface and the properties of a multi-species microbial community were just the sum of the constituent populations, then the scientific and clinical imperative for their study would be low. However, application of novel imaging (confocal or epifluorescence microscopy, fluorescence in situ hybridization, live ⁄ dead stains, etc.) and molecular techniques (16S rRNA gene amplification and sequence comparison, proteomics, transcriptomics, reporter gene technology, etc.) has radically altered our understanding of the biology of multi-species biofilms (Table 1), and key developments that are pertinent to the control of dental plaque are highlighted in this review. Another major shift in our understanding of microbial behaviour has come from our increased knowledge of microbial ecology (3), and recognition of the intimate relationship between the resident human microflora and the host. Changes in the host environment have a direct impact on gene expression, and thereby influence the metabolic activity, competitiveness and composition of the microflora, while the action of resident microorganisms can have consequences for the host. An appreciation of this dynamic relationship is critical to fully understand the relationship between the oral microflora and the host in health or disease.