Clinical investigation of bacterial species and endotoxin in endodontic infection and evaluation of root canal content activity against macrophages by cytokine production

This study investigated the presence of different Gram-negative bacterial species and the levels of endotoxins found in primary endodontic infection (PEI), determining their stimulation ability against macrophages through the levels of interleukin (IL)-1, IL-6, IL-10, and tumor necrosis factor alpha (TNF-α), and evaluated their relationship with clinical and radiographic findings. Samples were taken from 21 root canals with primary endodontic infection with apical periodontitis (PEIAP). Molecular techniques were used for bacterial detection. Limulus amebocyte lysate assay was used to measure endotoxins. Pro-inflammatory cytokines were measured by ELISA assay. All samples were positive for bacterial DNA (21/21). Prevotella nigrescens (57.2 %) was the most frequent species. Higher levels of endotoxins were found in teeth with pain on palpation and exudation (all p < 0.05). Positive correlations were found between endotoxins and the levels of TNF-α and IL-1β, whereas a negative correlation was found between endotoxin and the amount of IL-10 (p < 0.05). Endotoxin levels were found to be a risk factor for exudation and increased the number of Gram-negative bacterial species for the presence of a larger area of bone destruction (all p < 0.05). A wide variety of Gram-negative bacterial species are involved in primary endodontic infection, with participation of different Treponema species. Thus, the levels of endotoxins and the number of Gram-negative bacteria species present in root canals were considered risk factors for the severity of endodontic infection. The present study revealed that Gram-negative bacterial species and endotoxins play an important role in the development of signs/symptoms and the severity of bone destruction, this knowledge is essential for the establishment of an effective therapy.