Which microbe is unlikely to be isolated from a 7-day undisturbed supragingival biofilm?

• A. Streptococcus sanguis
• B. Actinomyces viscosus
• C. Candida albicans
• D. Entamoeba gingivalis

Answer: (D)

In supragingival biofilm, the community that develops over a week is made up mainly of bacteria that colonize the tooth surface early, starting with Streptococcus sanguis and Actinomyces viscosus. These organisms are classic early colonizers of the enamel pellicle and are commonly found in a 7-day, undisturbed plaque. Candida albicans can also be present in oral biofilms, especially in situations where the environment supports fungal growth, so its presence in supragingival plaque isn’t unusual. Entamoeba gingivalis, however, is a protozoan that typically resides in the gingival crevice or subgingival pockets, feeding on bacteria in those niches rather than in the open supragingival surface. Because of this preference for gingival sulcus/subgingival environments, Entamoeba gingivalis is unlikely to be isolated from a 7-day undisturbed supragingival biofilm.