Reclassification of Eubacterium combesii and discrepancies in the nomenclature of botulinum neurotoxin-producing clostridia: Challenging Opinion 69. Request for an Opinion

Int J Syst Evol Microbiol. 2018 Sep;68(9):3068-3075. doi: 10.1099/ijsem.0.002942. Epub 2018 Jul 30.


To clarify the taxonomic position of Eubacterium combesii, the whole genome of its type strain, DSM 20696T, was sequenced. Comparison of this sequence with known sequences of other bacteria confirmed that E. combesii represented a member of the Clostridium sporogenes/Clostridium botulinum Group I clade. However, the results of phylogenetic analysis also demonstrated that the latter two species did not form the same genetic entity and that E. combesii was in the C. botulinum Group I subclade. Meanwhile, we showed that E. combesii DSM 20696T did not produce botulinum neurotoxins (BoNTs) and thus should be identified as a strain of C. sporogenes in accordance with the current nomenclature of BoNT-producing clostridia, which is based, in particular, on Opinion 69 issued by the Judicial Commission of the ICSB. However, review of the corresponding Request for an Opinion revealed that it had been based on an erroneous statement. Therefore, we request reconsideration of Opinion 69 and propose to reclassify Eubacterium combesii as a later synonym of Clostridium botulinum. The results of phylogenetic analysis of the other five groups of BoNT-producing clostridia indicated that all the groups were far distant from each other. However, the members of Groups IV-VI are classified as strains of different species, while all members of Groups I-III are designated C. botulinum. Meanwhile, similarly to Group I, Groups II and III are also polyphyletic and appear to consist of two and four species, respectively. These results demonstrate, once again, discrepancies in the nomenclature of BoNT-producing bacteria and corroborate our request for reconsideration of Opinion 69.

Keywords: Clostridium; Eubacterium; botulinum neurotoxin; nomenclature revision; phylogenetic taxonomy; whole-genome sequencing.

MeSH terms

  • Bacterial Typing Techniques
  • Botulinum Toxins
  • Clostridium / classification
  • DNA, Bacterial / genetics
  • Eubacterium / classification*
  • Eubacterium / genetics
  • Phylogeny*
  • RNA, Ribosomal, 16S / genetics
  • Sequence Analysis, DNA


  • DNA, Bacterial
  • RNA, Ribosomal, 16S
  • Botulinum Toxins