- In endodontic infections, the environment within the root canals is typically low in oxygen, creating ideal conditions for certain types of microorganisms to thrive.
- Among these, obligate anaerobes are the most commonly found and predominate in such infections.

- Obligate anaerobes are bacteria that cannot survive in the presence of oxygen and thus prosper in the oxygen-deprived environment of infected root canals.
- These bacteria contribute significantly to the pathogenesis of endodontic infections due to their ability to produce various toxins and enzymes that damage periapical tissues.
- While facultative anaerobes and gram-positive aerobes may be present, they are usually less predominant compared to obligate anaerobes in chronic endodontic infections.
- Fungi are relatively rare and generally not the primary causative agents in endodontic infections.

Therefore, the correct answer is “Obligate anaerobes” because the anaerobic environment within the root canal favors their growth and predominance.

Reference: Cohen’s Pathways of the Pulp, 12th Edition, Chapter 6: Microbiology of Endodontic Infections, p. 188-190.