What is the predominant bacterial flora found in a healthy gingival sulcus?

A healthy gingival sulcus is dominated by Gram-positive, mostly aerobic/facultative, non-motile organisms (such as Streptococcus and Actinomyces species). As disease progresses (gingivitis → periodontitis), the flora shifts toward a higher proportion of Gram-negative, anaerobic, and motile organisms — the opposite of a healthy sulcus.