Clostridium tetani Gram-positive rods and large,
subterminal spores, deforming the cells.
Clostridium tetani
Cultural characteristics
Biochemical characters
Phylum Firmicutes, Class Clostridia, Order Clostridiales, Family Clostridiaceae, Genus Clostridium, Cluster I (Clostridium sensu
Clostridium tetani  (Flugge 1886) Bergey, Harrison, Breed, Hammer and Huntoon 1923.
Historical synonyms:
Bacterium tetani  Flugge 1886.
Gram-positive (become Gram-negative after 24 h incubation) straight rods, 0.5-1.7 x
2.1-18.1 µm, occuring singly or in pairs. Motility is variable. Spores are round/oval,
terminal/subterminal, swelling the cell. Cell wall is susceptible to dissolution by
Surface colonies on blood agar plates are 4–6 mm in diameter, flat, translucent, gray,
with a matt surface, irregular and rhizoid margins, and usually cause a narrow zone of
beta-hemolysis. Colonies in agar are transparent and very woolly. There is a tendency
to swarm that is more marked on moist plates. No aerobic growth on blood-agar.
Cultures in PYG (peptone, yeast extract and glucose) broth are turbid with a smooth or
ropy sediment and have a pH of 6.1–6.5 after incubation for 5 days.
Slight growth in nutrient broth, better in cooked meat broth. Moderate to abundant gas

is produced by most strains in PYG deep agar cultures.
Growth is inhibited by 6.5% NaCl but not by 20% bile. Grows at: 25-44 ºC, optimum at
37 ºC. Growth at 45 ºC is variable.
It is an ubiquitous organism. Source: soil throughout the world; human and other animal feces particularly horse feces.
Susceptible to chloramphenicol, clindamycin, erythromycin, penicillin G, and tetracycline.
Pathogenic for man and animals. Pathogenic for laboratory animals.
Two pathogenic soluble antigens, tetanolysin and tetanospasmin, are produced. Tetanospasmin, the cause of clinical tetanus in
humans and other animals, is an extremely potent neurotoxin. A “nonspasmogenic toxin” has been detected (in partially purified
form). A high molecular mass hemolysin that is distinct from tetanolysin has been detected.
Pathological sources: the atmosphere in a hospital; occasionally from wounds in animals and wounds in humans including infected
gums and teeth, corneal ulcerations, mastoid and middle ear infections, intraperitoneal infection, omphalitis (tetanus neonatorum),
postpartum uterine infections, various soft tissue infections related to trauma (including abrasions and lacerations), use of
contaminated needles and catgut.
  1. N.A. Logan and P. De Vos, 2009. Genus I. Clostridium Prazmowski 1880. In: (Eds.) P.D. Vos, G. Garrity, D. Jones, N.R. Krieg, W.
    Ludwig, F.A. Rainey, K.-H. Schleifer, W.B. Whitman. Bergey’s Manual of Systematic Bacteriology, Volume 3: The Firmicutes,
    Springer, 738-828.
  2. Smith L.D.S. and Hobbs G., 1975. Genus III. Clostridium Prazmowski 1880. In: (Eds.) Buchanan R.E. and Gibbons N.E., Bergey’s
    Manual of Determinative Bacteriology, Eighth Edition , The Williams & Wilkins Company, Baltimore, 551-572.
  3. Macovei A., 2009. Identificarea bacteriilor anaerobe. In: Tratat de Microbiologie Clinica (Ed. Buiuc D. si Negut M.), editia a IIIa,
    Editura Medicala, Bucuresti, 900-927.
  4. Secasiu V., 2001. Boli produse de germeni din genul Clostridium. In: Boli infectioase ale animalelor, Moga Manzat R., Ed. Brumar,
    Timisoara, 481-612.
  5. Standards Unit, Microbiology Services, PHE. UK Standards for Microbiology Investigations. Identification of Clostridium species.
    Bacteriology – Identification, ID 8, Issue no: 4, Issue date: 12.01.15.
H2 is produced very abundantly. Milk reaction and meat digestion are variable.

Positive results for H
2 production, DN-ase, gelatin hydrolysis, neutral red reduction,
and resazurin reduction.

Negative results for esculin hydrolysis, lecithinase, lipase, neuraminidase, nitrate
reduction, starch hydrolysis, urease, substrate utilized and/or acid produced from:
arabinose, amygdalin, cellobiose, fructose, galactose, glucose, glycogen, inositol,  
inulin, lactose, maltose, mannitol, mannose, melezitose, melibiose, raffinose,
rhamnose, ribose, salicin, sorbitol, starch, sucrose, trehalose, and xylose.

Variable results for indole and H
2S production.
(c) Costin Stoica
Culture media
Biochemical tests
Previous page