The most predominant bacteria in primary endodontic infections are:

Primary endodontic infections of necrotic pulp are predominantly caused by obligate (strict) anaerobes. Studies using culture-independent methods (16S rRNA gene sequencing) have confirmed that obligate anaerobes such as Fusobacterium nucleatum, Prevotella, Porphyromonas, Peptostreptococcus, and Treponema species are the dominant organisms. The necrotic pulp provides a low-oxygen, nutrient-rich environment that favors obligate anaerobic growth. Facultative anaerobes can survive but are not the predominant organisms in well-established primary infections.