Characterization of Actinomyces turicensis and Actinomyces radingae strains from human clinical samples

This study characterized previously unidentified coryneform bacteria from human clinical samples using whole-organism protein electrophoresis, fatty acid analysis, biochemical tests, and 16S rRNA gene sequencing. Researchers examined strains that had been provisionally named as resembling Gardnerella vaginalis, Actinomyces meyeri, Actinomyces pyogenes, Arcanobacterium haemolyticum, and CDC group E bacteria. The analyses revealed that the majority of isolates belonged to Actinomyces turicensis, while others were identified as Actinomyces radingae. These two Actinomyces species were originally described by Wüst and colleagues in 1995. The study included strains isolated from diverse human infections including abscesses, cysts, wound infections, and genitourinary conditions. Species-specific oligonucleotide probes based on 16S rRNA sequences were successfully designed to distinguish between the two species. The combined evidence from protein patterns, fatty acid composition, and genetic analysis confirmed that previously misidentified strains belonged to these two distinct species, and differential phenotypic tests were identified to distinguish them. The descriptions of both Actinomyces turicensis and Actinomyces radingae were amended based on these findings.

Key findings

• Most unidentified coryneform bacteria resembling Gardnerella vaginalis and various Actinomyces species were identified as Actinomyces turicensis, with remaining strains identified as Actinomyces radingae.
• Species-specific 16S rRNA oligonucleotide probes were designed that successfully distinguished between A. turicensis and A. radingae without cross-hybridization to other Actinomyces or Arcanobacterium species.
• The two species can be differentiated by multiple phenotypic tests including aesculin hydrolysis, acid production from lactose and salicin, and enzyme activities (leucine arylamidase in A. turicensis; galactosidases and glucosaminidase in A. radingae).
• Whole-cell protein electrophoresis and fatty acid analysis consistently grouped the cluster I and cluster II strains into distinct, homogeneous taxa correlating with the 16S rRNA findings.