Interaction between Staphylococcus aureus and Pseudomonas aeruginosa is beneficial for colonisation and pathogenicity in a mixed biofilm

Growth of oral bacteria in situ requires adhesion to a surface because the constant flow of host secretions thwarts the ability of planktonic cells to grow before they are swallowed. Therefore, oral bacteria evolved to form biofilms on hard tooth surfaces and on soft epithelial tissues, which often contain multiple bacterial species. Because these biofilms are easy to study, they have become the paradigm of multispecies biofilms. In this Review we describe the factors involved in the formation of these biofilms, including the initial adherence to the oral tissues and teeth, cooperation between bacterial species in the biofilm, signalling between the bacteria and its role in pathogenesis, and the transfer of DNA between bacteria. In all these aspects distance between cells of different species is integral for oral biofilm growth.

Coaggregation is a process by which genetically distinct bacteria become attached to one another via specific molecules. Cumulative evidence suggests that such adhesion influences the development of complex multi-species biofilms. Once thought to occur exclusively between dental plaque bacteria, there are increasing reports of coaggregation between bacteria from other biofilm communities in several diverse habitats. A general role for coaggregation in the formation of multi-species biofilms is discussed.