Name: Proteus inconstans (Ornstein 1920) Shaw and Clarke 1955 (Approved Lists 1980)

Category: Species

Proposed as: comb. nov.

Basonym: "Bacillus inconstans" Ornstein 1920

Etymology: in.con’stans. L. masc. adj. inconstans, changeable, inconstant, capricious

Pronunciation (Latin): … in-KON-stans

Type strain: ATCC 9886; CCUG 6325; CIP 82.90; DSM 30120; JCM 1673; NCTC 10286

See detailed strain information at

Conduct genome-based taxonomy at

16S rRNA gene: AJ301684 Analyse FASTA

Effective publication: Shaw C, Clarke PH. Biochemical classification of Proteus and Providence cultures. J Gen Microbiol 1955; 13:155-161.

IJSEM list: Skerman VBD, McGowan V, Sneath PHA. Approved lists of bacterial names. Int J Syst Bacteriol 1980; 30:225-420.

Nomenclatural status: validly published under the ICNP

Taxonomic status: synonym (and not recommended for medical use)

Correct name: Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980)

Risk group: 2

• Synonyms:

  • Name	Kind
    Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980)	homotypic synonym, validly published under the ICNP
    "Bacillus inconstans" Ornstein 1920	homotypic synonym, not validly published, basonym of name in Approved Lists
    "Eberthella alcalifaciens" de Salles Gomes 1944	homotypic synonym, not validly published, basonym of name in Approved Lists

• Notes:
  • ❗ Proteus inconstans is the correct name instead if this species is regarded as a separate species (i.e., if its nomenclatural type is not assigned to another species whose name is validly published, legitimate and not rejected and has priority) within a separate genus Proteus.
  • 😷 The risk group for Belgium has been imported on 2024-02-05. The full classification is: risk group = 2, note = "human pathogen". — The risk group for Canada has been imported on 2024-02-27. The full classification is: risk group = 2, note = "Animal classification RG: 1 - Security sensitive biological agent: No - Terrestrial animal pathogen under Canadian Food Inspection Agency authority: No - Containment level: Containment Level 2". — The risk group for Swiss Confederation has been imported on 2024-02-01. The full classification is: risk group = 2. — The risk group for Germany has been imported on 2026-08-13. The full classification is: risk group = 2, note = "ht". — 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 21 times in PubMed until 2026-06-11.
  • 🙅 This name is on the List of Recommended Names for bacteria of medical importance (LoRN) as a synonym of the name to be applied to this species. The name is on LoRN because of the recorded risk group of the species itself.
  • 🧍 On the Approved Lists of Bacterial Names and on the Approved Lists of Bacterial Names (Amended Edition) this nomenclatural name is incorrectly cited as Proteus inconstans (Orstein [sic] 1920) Shaw and Clarke 1955. — 🧍 On the Approved Lists of Bacterial Names incorrectly cited as Proteus inconstans (Orstein [sic] 1920) Shaw and Clarke 1955; name not in current usage; regarded as synonym of Providencia alcalifaciens, P. rustigianii or P. stuartii. Publication: Skerman VBD, McGowan V, Sneath PHA. Approved lists of bacterial names. Int J Syst Bacteriol 1980; 30:225-420.
  • 🧍 This name was subject to a comment on a Request for an Opinion. Publication: Li MS. On the priority between Yokenella regensburgei Kosako et al. 1985 and Koserella trabulsii Hickman-Brenner et al. 1985 and on the priority between Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980) and Proteus inconstans (Ornstein 1920) Shaw and Clarke 1955 (Approved Lists 1980). Requests for an Opinion. Int J Syst Evol Microbiol 2025; 75:6746. 🇹🇼
  • 🧍 The name Proteus inconstans is not in current usage. According to Brenner et al. [1] and to Hickman-Brenner et al. [2], (i) the strains gas -, inositol + of Proteus inconstans should be regarded as synonym of Providencia stuartii (Buttiaux et al. 1954) Ewing 1962; (ii) the strains gas +, inositol -, adonitol + should be regarded as synonym of Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962; and (iii) the strains glucose +, inositol -, adonitol - should be regarded as synonym of Providencia rustigianii Hickman-Brenner et al. 1983. Publication: Hickman-Brenner FW, Farmer JJ, Steigerwalt AG, Brenner DJ. Providencia rustigianii: a new species in the family Enterobacteriaceae formerly known as Providencia alcalifaciens biogroup 3. J Clin Microbiol 1983; 17:1057-1060. 🇺🇸

Parent taxon: Proteus Hauser 1885 (Approved Lists 1980)

Assigned by: Shaw C, Clarke PH. Biochemical classification of Proteus and Providence cultures. J Gen Microbiol 1955; 13:155-161.

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Record number: 779873