Black-pigmented bacteria have been implicated in the endodontic infections. This group of microorganisms includes Porphyromonas endodontalis, Porphyromonas gingivalis, Prevotella intermedia, and Prevotella nigrescens. The organisms display a wide variety of virulence factors that may be pertinent to acute endodontic infections.

The aim of this study was to identify P. endodontalis, P. gingivalis, P. intermedia, and P. nigrescens by using special potency disk test, filter paper spot test, 16S rRNA gene-directed PCR, and API 32A.

Microbial samples were collected from root canals of 33 intact teeth with necrotic pulp and/or apical periodontitis. Conventional laboratory methods were used for identification of the strains of black pigmented bacteria. Eighteen of 33 samples were positive for the growth of black-pigmented bacrteria. Five colonies were cultured from each pure cultured colonies from Brucella agar plate. Seventy seven colonies were positive for the growth of black-pigmented bacteria.

Thirty three of 77(42.6%) were identifed as P. nigrescens, 10 of 77(12.9%) were P. gingivalis, 6 of 77(7.8%) were P. endodontalis, 10 of 77(12.9%) were P. intermedia. On the contrary the reference strains of P. nigrescens, experimental strains of P. nigrescens was sensitive to kanamycin in special potency disk test.

16S rRNA gene PCR and API test after rapid presumptative identification methods, such as special potency disk test and filter paper spot test, would be accurate detection methods for black-pigemented bacteria.