Actinomyces europaeus sp. nov., Isolated from Human Clinical Specimens

This study describes the identification and characterization of a previously unknown coryneform bacterium isolated from human clinical specimens, primarily from abscesses. Ten strains collected from three European laboratories were characterized using a polyphasic approach combining biochemical testing, chemotaxonomic analysis, and 16S rRNA gene sequencing. The organisms were catalase-negative, facultatively anaerobic, gram-positive rods that fermented glucose and maltose but not mannitol or xylose. Biochemical profiles initially resembled Arcanobacterium bernardiae and CDC coryneform group E bacteria, but differed in key characteristics. Cellular fatty acid analysis and peptidoglycan composition (L-lysine-L-lysine-D-glutamic acid type) supported assignment to the genus Actinomyces. 16S rRNA sequence analysis demonstrated the strains formed a distinct lineage with less than 92% sequence similarity to established Actinomyces species. Whole-cell protein profiles showed all seven tested strains clustered together with >80% correlation. The organisms displayed susceptibility to beta-lactams and glycopeptides consistent with known Actinomyces species. Based on these findings, the authors propose a new species, Actinomyces europaeus sp. nov., with type strain CCUG 32789A.

Key findings

• Ten clinical isolates of a previously undescribed catalase-negative, facultatively anaerobic coryneform bacterium from human abscesses were identified as a new Actinomyces species through polyphasic taxonomy.
• 16S rRNA gene sequence analysis showed <92% homology with established Actinomyces species, demonstrating the isolates represent a distinct phylogenetic lineage within the genus.
• The new species, Actinomyces europaeus sp. nov., is characterized by production of succinic acid as main fermentation end product and peptidoglycan type A4a (L-lysine-L-lysine-D-glutamic acid).
• All ten strains showed high genetic and phenotypic homogeneity, with protein profile analysis demonstrating >80% within-group correlation and clustering distinct from other Actinomyces and Arcanobacterium species.