[Comparison of the activity against Streptococcus mutans of a chlorhexidine-based antiseptic as a suspension or as a biofilm]

Abstract

When bacteria colonize a surface they form a biofilm whose susceptibility to anti-microbials is different from that of the same bacterial species forming a homogeneous suspension in a liquid. This study investigated colonization of an inert solid phase (Tygon) with Streptococcus mutans ATCC 25,175--one of the strains involved in the initiation of cariogenic dental plaque--in a continuous flow of fresh medium sufficiently diluted so as to preclude growth of suspended bacteria. Only those bacteria which adhered to the solid phase grew, forming a biofilm. The antiseptic activity of Eludril (0.1% chlorhexidine) on this biofilm under dynamic (flowing medium) and static (stagnant medium) conditions was studied by comparison with the same strain in a suspension (in compliance with the AFNOR NF T 72-150 norm) and in a confluent culture on a filtering membrane. The biofilm was less susceptible under dynamic than under static conditions; under both conditions, the biofilm was less susceptible than the suspension. According to this model, the concentration of antiseptic recommended by the manufacturer according to studies using AFNOR norm NF T 72-150 (bacteria in a suspension) may be inadequate for bacteria adhering to tooth surfaces or gingival mucosa.