Dialister invisus sp. nov., isolated from the human oral cavity

This study describes the characterization and naming of a previously unnamed bacterial species isolated from human oral infections. Six strains of anaerobic, gram-negative coccobacilli were recovered from root canals of endodontic infection patients (five strains) and a periodontal pocket (one strain). These strains were subjected to comprehensive phenotypic and genetic analysis. Based on 16S rRNA gene sequencing, the isolates showed 93% sequence similarity to Dialister pneumosintes but were phylogenetically and phenotypically distinct enough to warrant recognition as a novel species. The new organism, named Dialister invisus, is biochemically largely unreactive and asaccharolytic, producing only trace amounts of acetate and propionate. The organism shows characteristic gram-negative cell wall ultrastructure, grows as small coccobacilli, and produces minimal turbidity in broth cultures. DNA-DNA relatedness with D. pneumosintes was 42%, and the G+C content was 45-46 mol%, higher than D. pneumosintes at 35 mol%. The type strain E7.25T and the species proposal expand knowledge of oral anaerobic bacteria associated with endodontic and periodontal infections.

Key findings

• Dialister invisus sp. nov. is a novel species of anaerobic, gram-negative coccobacilli isolated from human oral infections, with 93% 16S rRNA sequence similarity to D. pneumosintes
• D. invisus is biochemically unreactive and asaccharolytic, producing only trace metabolic end-products of acetate and propionate
• DNA-DNA relatedness between D. invisus and D. pneumosintes is only 42%, with substantially different G+C content (45-46 mol% versus 35 mol%)
• The organism produces minimal broth culture turbidity and lacks visible growth stimulation by carbohydrates, leading to the species name 'invisus' (unseen)
• D. invisus was the sole organism detected in some chronic endodontic infections, suggesting a role in oral infections