Which bacteria is commonly associated with periodontitis?

Porphyromonas gingivalis is a key pathogen associated with periodontitis. This bacterium is a gram-negative anaerobe that significantly contributes to the development and progression of periodontal disease. Its presence in the periodontal microbiota is characterized by the ability to evade the host's immune response, promote inflammation, and destroy periodontal tissue.

P. gingivalis produces various virulence factors, including proteases that can degrade host proteins and interfere with immune signaling pathways. This means that it not only plays a role in the destruction of the periodontal tissues but also helps create an environment that allows other pathogenic microorganisms to thrive, exacerbating the disease.

In contrast, the other bacteria listed, while they have roles in oral health and disease, are not primarily linked to periodontitis. For instance, Streptococcus mutans is primarily associated with dental caries, Lactobacillus casei is often linked to fermented foods and does not play a significant role in periodontal disease, and Enterococcus faecalis is more related to endodontic infections. Thus, P. gingivalis stands out as the most relevant bacterium in the study of periodontitis.