Apical periodontitis microbiome association with salivary and serum inflammatory burden

Apical Periodontitis (AP) involves complex interactions between the root canal microbiome and the host immune response, with potential risk of local and systemic inflammatory burden, however there is no evidence available regarding correlation between microbiome and inflammatory marker levels. This study aims to identify the microbiome of saliva, intracanal and blood samples in AP subjects and investigate the correlation between intracanal and blood microbiomes with serum inflammatory biomarker levels, and salivary microbiomes with salivary inflammatory biomarker levels.

Saliva, Intracanal and blood samples were collected from AP patients undergoing root canal retreatment. Following DNA extraction, 16SrRNA gene-sequence analysis (V1-V2) was performed using Illumina MiSeq 300 platform. Serum and salivary inflammatory marker levels were measured using the magnetic multiplex-microbead assay. The alpha and beta diversities were tested using the phyloseq package in R (version 4.1). The abundance of the identified phyla and genera were analysed using non-parametric tests. Spearman´s correlation coefficient was used for correlation between microbial abundance and biomarker levels.

Streptococcus and Prevotella were prevalent in saliva; Enterococcus, Streptococcus and Bacteroidaceae_(G-1) in intracanal; and Cutibacterium and Staphylococcus in blood samples. Streptococcus, Prevotella, Actinomyces and Rothia were the most abundant common genera among all three sample sources. In saliva, Haemophilus, Gemella, Prevotella, and Alloprevotella were positively correlated with salivary levels of IL-8, MMP-2, TNF-α, and IL-6, respectively. Intracanal genera, Enterobacter, and Parvinomonas, were positively correlated serum FGF-23. Finally, the abundance of Novosphingobium, Streptococcus, Bosea, and Corynebacterium genus in blood were positively correlated with FGF-23, MMP-9, CRP, IL-8, and ICAM-1.

Microbiome in saliva, blood and intracanal samples were correlated with some of the inflammatory biomarker levels of saliva and serum, suggesting that the effect of AP goes beyond a periapical infection and may pose a potential systemic inflammatory burden risk if left untreated.