Dental caries is a chronic disease that occurs in 80% of the adult population. In each stage of caries development typical microflora is found. The bacteria S. mutans, S. sobrinus and Lactobacillaceae play a crucial role in the carious process. Lack of caries treatment may result in primary root canal infection and inflammation of the periapical tissues. In root canal systems with primary infections, 90% of the bacterial microflora is anaerobic bacteria. Intracanal infections and coronal leakage are the most frequent reasons for failures in primary endodontic treatment. During secondary infection, the root canal system is colonized by relatively anaerobic G+ bacteria. E. faecalis is a pathogen of the greatest clinical importance which may constitute more than 70% of the bacteria in the root canal. The article presents detailed information on S. mutans and E. faecalis with an emphasis on the role they play in the carious process as well as infections of periapical tissues, taxonomy, cell morphology, antibiotic resistance, antibiotic susceptibility and metabolism.

Key words: dental caries, S. mutans, E. faecalis.