A New Model for the Formation of an Endodontic Biofilm

by Elio and Roberto
 

As we speak, biofilms are the rage in micro­biology. And why not, being that most bac­teria in nature are not free-swimming but are at­tached to some sur­face. Model sys­tems for bio­films are there­fore sorely needed. Research­ers from two instit­utions in Bogotá, Colombia, the Univer­sidad del Bosque and the Univer­sidad de los Andes (with Diana M. Castillo as the senior author) com­bined forces to dev­elop a novel model for bio­film for­ma­tion by Enterococcus faecalis. This path­ogen thrives both in the human gut and on the sur­face of teeth. It is also found in the root canals, where it can cause ser­ious endo­dontic infec­tion.
 

Fig.1. Three-dimensional reconstruction of confocal laser scanning microscopy im­ages of bio­film for­ma­tion in cer­vical, middle, and api­cal sur­faces at three time points. Green fluor­escence cor­res­ponds to via­ble bac­teria, red fluor­escence cor­res­ponds to non­viable bac­teria. Scale bars = 50 µm. Source. Fron­­­tis­­piece.

The model in ques­tion con­sists of grow­ing Enterococcus faecalis on the sur­face of the roots of teeth, pieces of den­tin (the middle layer of the tooth, bet­ween the ena­mel and the pulp), cut from healthy freshly extrac­ted (for ortho­dontic pur­poses) human teeth and sur­face steril­ized before being inoc­ulated with E. faecalis cul­tures. The samples were incu­bated for up to a month to sim­ulate the con­ditions in a real infec­ted tooth. Bac­teria on the den­tin root sur­face were enum­erated and exam­ined using two ap­proaches: field emis­sion scan­ning elec­tron micro­scopy and con­focal laser scan­ning micro­scopy. After 14 days, the root sur­faces became homo­genously colo­nized and most of the cells were viable as judged by the SYTO9/­propidium iodide live/­dead stain­ing. By 30 days more than half the cells were dead. To para­phrase the words of the authors, "this new in vitro E. faecalis bio­film for­mation endo­dontic model has an appro­priate bio­volume and a stable three-dimensional struc­ture. It is com­patible with a mature bio­film under con­ditions of nutri­tional restric­tion, as usually occurs in the endo­dontic environ­ment. It should allow future eval­uation of the effi­cacy of anti­micro­bial sub­stances with a more clin­ical ap­proach." It sounds like they are ready to go.