Black-pigmented bacteria (BPB) have been associated with infections of endodontic origin. The purpose of this study was to culture and identify BPB from the apical and coronal segments of infected root canals to understand better their ecological relationships. Teeth with a periapical radiolucency were extracted and immediately placed in reduced transport fluid for transport to an anaerobic chamber. Of 18 sampled roots, 12 were positive for the growth of BPB. Eight of the 12 roots with BPB had a carious exposure of the pulp chamber. Seven roots had Prevotella nigrescens in both the apical and the coronal segments. Six of these seven teeth had carious exposures of the pulp chamber. Of the 12 roots infected with BPB, six roots had two different species of BPB, with P. nigrescens always being one of the species. P. nigrescens was the most often isolated BPB from both the coronal and apical segments of infected root canals.
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