Oral Actinomyces isolates forming red colonies on brain heart blood agar can bee unambiguously classified as A odontolyticus by macroscopic examination

Abstract

The accurate classification of oral Actinomyces isolates as one species is difficult. Out of 18 Actinomyces isolates forming red colonies on brain heart blood agar, 12 could be straightforwardly assigned as Actinomyces odontolyticus by biochemical, morphological, and chemotaxonomic characteristics. For the remaining six isolates, the results of the different identification methods were inconsistent. By sequencing a 16S ribosomal DNA fragment by a rapid mass spectrometric method, all isolates could be identified unambiguously as A. odontolyticus. This result proves the importance of red colony pigmentation on brain heart blood agar together with the characteristic cell morphology for unequivocal assignment of oral Actinomyces isolates to the species A. odontolyticus.

FIG. 1.

MALDI-TOF mass spectrum of the Sanger sequencing products of the PCR-amplified 16S rDNA fragment of an Actinomyces isolate from the Caries Risk Assessment Study of Erfurt. The first peak (m/z 3,840.4 Da) represents the unextended primer.