Name: Clostridioides difficile (Hall and O'Toole 1935) Lawson et al. 2016

Category: Species

Proposed as: comb. nov.

Basonym: "Bacillus difficilis" Hall and O'Toole 1935

Etymology: dif.fi’ci.le. L. neut. adj. difficile, difficult (referring to “the unusual difficulty that was encountered in its isolation and study”)

Pronunciation (Latin), gender: … dif-FI-ki-le, neuter

Type strain: ATCC 9689; BCRC 10642; CCRC 10642; CCUG 4938; CGMCC 1.2184; CIP 104282; DSM 1296; JCM 1296; LMG 15861; NCIB 10666; NCIMB 10666; NCTC 11209

Conduct genome-based taxonomy at

16S rRNA gene: AB548672 Analyse FASTA

Effective publication: Lawson PA, Citron DM, Tyrrell KL, Finegold SM. Reclassification of Clostridium difficile as Clostridioides difficile (Hall and O'Toole 1935) Prevot 1938. Anaerobe 2016; 40:95-99. 🇺🇸

IJSEM list: Oren A, Garrity GM. Validation list no. 171. List of new names and new combinations previously effectively, but not validly, published. Int J Syst Evol Microbiol 2016; 66:3761-3764.

Nomenclatural status: validly published under the ICNP

Taxonomic status: correct name (and explicitly recommended for medical use)

Risk group: 2

• Synonyms:

  • Name	Kind
    "Peptoclostridium difficile" (Hall and O'Toole 1935) Yutin and Galperin 2013	homotypic synonym, not validly published
    Clostridium difficile (Hall and O'Toole 1935) Prévot 1938 (Approved Lists 1980)	homotypic synonym, validly published under the ICNP
    "Bacillus difficilis" Hall and O'Toole 1935	homotypic synonym, not validly published, basonym of name in Approved Lists

• Notes:
  • 🥇 Nomenclatural type of the genus Clostridioides Lawson et al. 2016. Publication: Lawson PA, Citron DM, Tyrrell KL, Finegold SM. Reclassification of Clostridium difficile as Clostridioides difficile (Hall and O'Toole 1935) Prevot 1938. Anaerobe 2016; 40:95-99. 🇺🇸
  • 😢 The terminology used by the authors is in line with many other taxonomic studies and does not negatively affect their main results; some improvements may nevertheless be possible. Contrasting the term "chemotaxonomic" with "phenotypic" is not recommended. Whether taxa can have "members" is debatable. See the LPSN phylogeny page for details. Publication: Göker M. What can genome analysis offer for bacteria? In: Bridge P, Smith D, Stackebrandt E (eds), Trends in the systematics of bacteria and fungi, CAB International, Wallingford, 2021, p. 255-281. 🇬🇧
  • 😷 The risk group for Belgium has been imported on 2024-02-05. The full classification is: risk group = 2, note = "human and animal pathogen - human: T - biological class of risk animal: 2". — The risk group for Canada has been imported on 2024-02-27. The full classification is: risk group = 2, note = "Clostridium difficile: 2 Animal classification RG: 2 - Security sensitive biological agent: No - Terrestrial animal pathogen under Canadian Food Inspection Agency authority: No - Containment level: Containment Level 2". — The risk group for Germany has been imported on 2023-10-29. The full classification is: risk group = 2. — The risk group for Taiwan has been imported on 2024-11-03. The full classification is: risk group = 2, note = "P650 = v". — The risk group for United Kingdom has been imported on 2024-01-31. The full classification is: risk group = 2, note = "Toxigenic". — If in doubt, use the risk group given in the regulations for your country and, if these are not available, use the risk group given in the catalogue of the culture collection from which you have obtained or intend to obtain the strain.
  • 🎓 Name mentioned 4960 times in PubMed until 2025-06-04.
  • 🙆 This name is on the List of Recommended Names for bacteria of medical importance (LoRN) as the name to be applied to this species. The name is on LoRN because of the recorded risk group of the species itself.
  • 🧍 According to Bartlett et al. (2022), this species is an established human pathogen. Publication: Bartlett A, Padfield D, Lear L, Bendall R, Vos M. A comprehensive list of bacterial pathogens infecting humans. Microbiology (Reading) 2022; 168:0. 🇬🇧
  • 🧍 See Oren and Rupnik (2018) for details on the nomenclature of this species. Publication: Oren A, Rupnik M. Clostridium difficile and Clostridioides difficile: Two validly published and correct names. Anaerobe 2018; 52:125-126. 🇮🇱
  • 🧍 The genome of the type strain was sequenced as part of the GEBA (Genomic Encyclopedia of Bacteria and Archaea) project. Publication: Mukherjee S, Seshadri R, Varghese NJ, Eloe-Fadrosh EA, Meier-Kolthoff JP, Goker M, Coates RC, Hadjithomas M, Pavlopoulos GA, Paez-Espino D, et al. 1,003 reference genomes of bacterial and archaeal isolates expand coverage of the tree of life. Nat Biotechnol 2017; 35:676-683. 🇺🇸

Parent taxon: Clostridioides Lawson et al. 2016

Assigned by: Lawson PA, Citron DM, Tyrrell KL, Finegold SM. Reclassification of Clostridium difficile as Clostridioides difficile (Hall and O'Toole 1935) Prevot 1938. Anaerobe 2016; 40:95-99. 🇺🇸

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Record number: 794449