Characterization of intratissue bacterial communities and isolation of Escherichia coli from oral lichen planus lesions.

Oral lichen planus (OLP) is a chronic T cell-mediated inflammatory disease of unknown etiology. We previously proposed that the intracellular bacteria detected in OLP lesions are important triggering factors for T cell infiltration. This study aimed to identify OLP-associated bacterial species through the characterization of intratissue bacterial communities of OLP lesions. Seven pairs of bacterial communities collected from the mucosal surface and biopsied tissues of OLP lesions were analyzed by high-throughput sequencing of the 16S rRNA gene. The intratissue bacterial communities were characterized by decreased alpha diversity but increased beta diversity compared with those on the mucosal surface. While the relative abundance of most taxa was decreased within the tissues, that of Escherichia coli was significantly increased. Four E. coli strains were isolated from additional OLP biopsies and verified as K12 strains by whole-genome sequencing. The distribution of E. coli in sections of control (n = 12) and OLP (n = 22) tissues was examined by in situ hybridization. E. coli was detected in most OLP tissues, suggesting its potential role in the pathogenesis of OLP. The oral E. coli strains isolated from OLP tissues will be useful to investigate their role as triggering factors for T cell infiltration.