Oral bacterial biofilms – history in progress

Ask microbiologists what the word 'biofilm' brings to mind, and many would speak about Pseudomonas aeruginosa, about microtitre plates or flowcells, about 'mushrooms' and 'voids', and about antibiotic resistance and device-related infections. They would perhaps speak of biofilm growth as development: distinct phases or behaviours such as attachment, spreading and dispersal. They would almost certainly mention quorum sensing or communication, and almost all would use the word 'community' or 'population'. Yet, despite their well-founded enthusiasm and the numerous impressive examples they would cite, the populations to which they typically refer are in fact quite homogeneous; most of what is clearly recognized as biofilm research has been conducted in vitro using single bacterial pure cultures. However, working in relative obscurity and beginning several decades prior to popularization of the word biofilm, oral microbiologists established the paradigm for our understanding of development in real-world biofilm communities: dental plaque. Irene Dige and colleagues continue this tradition in the current issue of Microbiology by describing and quantifying the spatiotemporal population dynamics of Actinomyces naeslundii in early supragingival biofilms (Dige et al., 2009). Historically, examination of biofilm growth at the level of single cells began in earnest when the elecron microscope became a common biological tool. Microbiologists and 'cariologists', especially those in Scandinavian dental schools, used this tool to study the most easily accessible biofilms of the human body: those that form on tooth surfaces. The biofilms were retrieved at sequential time points on small pieces of glass or bovine enamel that had been carried in the oral cavity of a volunteer: typically an eager(?) student. To isolate, count, and identify organisms after removal, the biofilm was scraped off, homogenized, and plated on various media. With the perfect hindsight that the oral cavity is home to some 800 phylotypes, and compounded by the relatively rudimentary speciation techniques at the time, this approach was laborious, duplicative, and often yielded datasets that were difficult to compare from laboratory to laboratory. However, one arrived at the conclusion that a lot of different bugs were present, and one could say that the great majority of those were streptococci, with other bacteria such as actinomyces also present. Carrier pieces were simultaneously examined with the electron microscope. Early on (¡4 h of carrier wear), the biofilm consisted of small aggregates of spherical cells (generally no more than three or four cells) with the occasional non-coccoid morphotype thrown in. As time progressed, …