What type of bacteria are primarily responsible for gingival edema?

Gingival edema, or swelling of the gums, is primarily caused by anaerobic bacteria. These bacteria thrive in low-oxygen environments, such as subgingival plaque, which accumulates below the gum line. In healthy conditions, the flora in the mouth includes both aerobic and anaerobic bacteria; however, in the presence of periodontal disease, the balance shifts, and anaerobic bacteria become more prevalent.

These anaerobic bacteria play a critical role in the inflammatory processes associated with periodontitis and gingivitis. They can produce various virulence factors, such as toxins and enzymes, which contribute to tissue breakdown and inflammation, leading to the classic signs of gingival edema, including redness, swelling, and tenderness of the gums.

While aerobes, facultative anaerobes, and Gram-positive bacteria can also be part of the oral microbiome, they do not primarily drive the processes that result in gingival edema. This condition is most closely linked to the overgrowth of anaerobic bacteria, which is why this choice is the most appropriate answer.