The family Coriobacteriaceae: reclassification of Eubacterium exiguum (Poco etal. 1996) and Peptostreptococcus heliotrinreducens (Lanigan 1976) as Slackia exigua gen. nov., comb. nov. and Slackia heliotrinireducens gen. nov., comb. nov., and Eubacterium lentum (Prevot 1938) as Eggerthella lenta gen. nov., comb. nov.

Wade, William G., Downes, Julia, Dymock, David, Hiom, Sarah J., Weightman, Andrew J., Dewhirst, Floyd E., Paster, Bruce J., Tzellas, Nia, Coleman, Brittney

International Journal of Systematic and Evolutionary Microbiology 1999; 49(2):595 · https://doi.org/10.1099/00207713-49-2-595

Summary auto-generated

This study used 16S rRNA gene sequencing to clarify the taxonomic positions of three difficult-to-identify anaerobic bacteria previously misclassified within the genera Eubacterium and Peptostreptococcus. Analysis revealed that Eubacterium exiguum, Peptostreptococcus heliotrinreducens, and Eubacterium lentum belong to the Coriobacteriaceae family, a high-GC Gram-positive group, rather than with typical low-GC Eubacterium species. Based on 16S rRNA sequence similarity and phenotypic characteristics, particularly bile sensitivity and resistance, the authors propose creating two new genera. Slackia gen. nov. includes the bile-sensitive species E. exiguum and P. heliotrinreducens, renamed as Slackia exigua and Slackia heliotrinireducens. Eggerthella gen. nov. includes the bile-resistant E. lentum, renamed Eggerthella lenta. These organisms were previously confused due to unreactive biochemical profiles. The reclassification resolves longstanding taxonomic uncertainty and clarifies the phylogenetic relationships of these medically relevant bacteria, particularly E. exiguum, which is frequently isolated from oral infections and periodontitis.

Key findings

Three anaerobic bacteria—Eubacterium exiguum, Peptostreptococcus heliotrinreducens, and Eubacterium lentum—belong to the high-GC Gram-positive family Coriobacteriaceae, not the low-GC Eubacterium sensu stricto group.
Two new genera are proposed: Slackia (containing the bile-sensitive species S. exigua and S. heliotrinireducens) and Eggerthella (containing the bile-resistant E. lenta).
Eubacterium exiguum and Peptostreptococcus heliotrinreducens showed 94.7% 16S rRNA sequence similarity and are closely related bile-sensitive organisms commonly found in oral infections.
Bile sensitivity and resistance serve as key phenotypic characteristics distinguishing Slackia species from Eggerthella lenta and aid in their differentiation.

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Abstract

16S rRNA gene sequences were determined for Eubacterium exiguum and Peptostreptococcus heliotrinreducens. These species were found to be closely related and, together with Eubacterium lentum, to constitute a branch of the Coriobacteriaceae. Two new genera are proposed on the basis of phenotypic characteristics and 16S rRNA gene sequence comparisons: Slackia to include the bile-sensitive species Eubacterium exiguum and P. heliotrinreducens, and Eggerthella to include the bile-resistant Eubacterium lentum. It is proposed that Eubacterium exiguum and Peptostreptococcus heliotrinreducens are transferred to the genus Slackia gen. nov. as Slackia exigua gen. nov., comb. nov. (type strain ATCC 700122^T) and Slackia heliotrinireducens gen. nov., comb. nov. (type strain NTCC 11029^T). respectively, and Eubacterium lentum is transferred to the genus Eggerthella gen. nov. as Eggerthella lenta gen. nov., comb. nov. with Eggerthella lenta as the type species.