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.