Clostridium tetani: A Comprehensive Guide

Clostridium tetani is a causative agent of disease known as tetanus. Spores of Clostridium tetani are responsible for disease which is commonly found in soil, ash, feces of human and gut and feces of some animal and on the surface of rusty tools such as needles, nails, wire etc.

Tetanus does not spread from human to human but can penetrate through wounds, burns. The spores are resistant to heat and most of the antiseptics due to which it survives for years. 

Taxonomy and Classification

Domain: Bacteria

Kingdom: Bacillati

Phylum: Bacillota

Class: Clostridia

Order: Eubacteriales

Family: Clostridiaceae

Genus: Clostridium

Species: C. tetani

Morphology and Microscopy

• Gram positive, rod –shaped bacilli 
• Approximately 0.5 µm wide and 2.5 µm long in size that occur singly or in chain.
• Motile by peritrichous flagella
• Non capsulated
• Spore forming
• Contain spores that are spherical, terminal and bulging with drumstick appearance.

Under microscope, they are seen as pink colored rod shaped bacilli with green colored spores.

Cultural and Growth Characteristics

• Obligate anaerobes
• Optimum temperature: 37˚C
• Optimum pH: 7.4
• Grows fairly in ordinary media with burnt organic smell.
• Nutrient Agar: swarming growth, irregularly round, 2-5mm in diameter, grayish yellow with granular surface, translucent, ill-defined edges.
• Blood Agar: shows β-hemolysis.
• Cooked Meat Medium: grows well with turbidity and gas formation. Meat is not digested but turns black after long incubation.
• Lactose Egg Yolk Milk Medium: no proteolysis or lactose fermentation, no opalescence, no pearly layer.

 Fig 1: Microscopic Structure of C. tetani

Source: https://www.researchgate.net/figure/a-Spores-and-bacteria-of-Clostridium-tetani-with-a-typical-drum-stick-shape-isolated_fig1_277205153

Biochemical and Identification Tests

Pathogenesis and Virulence Factors

• Clostridium tetani breaks into the body via wound lacerations where many cells are dead.
• Then the spores germinate in the presence of anaerobic conditions
• After that, toxins which are harmful to the human nervous system are produced and circulated through blood and lymphatics.
• Among various toxins produced, tetanospasmin also known as tetanus toxin, binds at various sites in the central nervous system, including peripheral motor end plates, spinal cord and brain and also in the sympathetic nervous system.
• The clinical findings begin when toxin obstructs with the release of neurotransmitters, hindering inhibitor impulses.
• Spasms occur in the pharyngeal muscles which cause difficulty while swallowing.
• This can then lead to seizures and can affect autonomic nervous systems causing death.

C. tetani produces two types of exotoxins which functions as virulence factor which are explained below:

• Tetanolysin

• Is a Heat-liable and oxygen liable toxin.
• Acts as leucotoxin
• It is hemolysin which is antigenically related to the oxygen-liable hemolysins generated by C. perfringens , S. pyogenes. 
• It destroys living tissues adjacent to the infection and enhances the multiplication of bacteria.
• Tetanospasmin

• Is proteinous in nature
• Is a Heat liable but oxygen stable toxin 
• Is plasmid-encoded neurotoxin
• Responsible for clinical manifestations of tetanus.
• It is antigenic and is specifically neutralized by antitoxin.
• Obstructs the inhibitory nerve impulses by hindering the release of neurotransmitters which cause spastic paralysis.

Epidemiology and Transmission

Tetanus occurs mostly in developing countries where there is deficiency in immunity, and in those areas which are affected by natural disasters. In the US, between 2001 and 2008 the average incidence of tetanus was 0.01% in 100,000 populations. Then in 2009 to 2015, 197 cases of tetanus were reported with 16 deaths in the US. In the European Union, during 2023, 73 cases of tetanus were reported among which 13 were confirmed cases which has increased in comparison to previous year. The graph of tetanus virus infection shows a decline in 2019 with 69 cases to 32 cases in 2020 which is accompanied by a rise with 50 cases in 2021 and 53 cases in 2022. The highest risk group are new born, women and old aged people. 13 fatal tetanus cases reported in 2023 were reported in women aged above 79. In 2010, there were 1822 cases of tetanus in Uganda and 1038 cases in DRC which accounts for 50% cases in Africa. In 2015, about 56,000 tetanus related deaths were reported worldwide among which 35% occurred in newborns. Tetanus is often related to trauma and open wounds of all sizes and types. Similarly, tetanus is most common in pregnant women and newborns who are not properly vaccinated and delivered in unhygienic environments. 

C. tetani is transmitted through various ways:

• Bacteria are transmitted from soil or through dirty nails.
• Spread through dirty knives and tools which contaminate wounds and cuts.
• Newborns can be infected by instruments used to cut umbilical cord which is dirty or contaminated with soil.
• During surgery which is carried out without proper asepsis.
• Spreads through injury such as wounds, superficial abrasions.

Risk factors

There are various risk factors associated with C. tetani infection which are listed below:

• Age above 65 years
• Immunocompromised person having other disease
• Person having no vaccination
• Those who had outdated tetanus booster shots
• Those who are using intravenous drugs
• People having co-morbidities such as diabetes mellitus

Similarly, natural disasters such as landslides, earthquakes, tsunamis and hurricanes are not responsible for the rise in the tetanus level in the environment; however, cases of tetanus may elevate throughout the disasters since wounds lead to tetanus exposure. 

Clinical Manifestations

Incubation period is generally 8 days, but it can range from 1 to 21 days. There are 3 forms of infection which are caused by C. tetani. 

• Generalized Tetanus

• It is the most common type with more than 80% reported cases.
• Is presented in descending pattern
• Trismus
• Lockjaw
• Stiffness of neck
• Difficulty in swallowing
• Rigidity in abdominal muscles
• Sweating
• Elevation in temperature
• Rise in blood pressure
• Increase in heart rate
• Spasms 

These symptoms last for 3 to 4 weeks and complete recovery may take months.

• Localized Tetanus

• It is an uncommon type of tetanus.
• Persistent contraction of muscles near the site of the wound.
• It is milder and can progress to generalized tetanus.
• Cephalic Tetanus

• It is a rare form of tetanus which results from a wound.
• Results in weakened face muscles and cause spasms of jaw muscles of jaw.
• Involves cranial nerves, especially in the facial area.
• Occurs occasionally along with otitis media in which C. tetani is found as the flora of the middle ear or following head wound.
• Neonatal Tetanus

• Is a form of generalized tetanus that occurs commonly in newborn infants.
• Found in infants born without protective passive immunity.
• Occurs commonly via infection of the unhealed umbilical stump.
• Symptoms usually appear from 4 to 14 days after birth.

There are some complications of tetanus which are listed below:

• Fractures
• Hypertension and/or abnormal heart rhythm
• Aspiration pneumonia
• Nosocomial infections
• Pulmonary embolism
• Laryngospasm
• Death

Laboratory Diagnosis

• Sample Collection
• Wound swabs and excised bits of tissues from the necrotic depths of wounds are used as samples.
• Gram Staining
• Appears as pink rod shaped bacilli with terminal and round spores as drum stick appearance.
• Culture

• Specimens are inoculated on suitable culture media.
• Then the inoculated plates are incubated at 37˚C for 24-48hrs.
• Nutrient Agar: swarming growth, irregularly round, grayish yellow with granular surface, translucent colonies.
• On Blood Agar: swarming growth which spreads throughout the plate.
• On Robertson Cooked Meat (RCM) Media: converts meat particles black and produces foul odor.
• Biochemical Tests

After culture, colonies from incubated plates are performed for biochemical tests and identified C. tetani based on following results:

• Toxigenicity Test

Various strains of C. tetani are tested for toxin production by following ways:

• Invitrohemolysis inhibition test

• Shows hemolysis on part of blood agar without any antitoxin but do not show any hemolysis on part with antitoxins.
• This is because of the inhibition of hemolytic activity of the toxin by antitoxin which is present in the agar.
• In vivo mouse inoculation test

• RCM broth having black turbid growth is inoculated in the tip of the tail of the experiment mouse.
• Then the tested animal develops stiffness in tail which progresses to hind limbs at the side where inoculation was done. 
• Then it proceeds to the limb of the other side then to the trunk and forelimbs.
• Death may occur within 2 days.
• Spatula Tests

• Is the most useful and simple bed-side diagnostic test.
• It is based on touching the oropharynx with a spatula or tongue blade.
• This test especially induces a gag reflex.
• If a person tries to throw out a spatula it is diagnosed as a negative test but if a person bites the spatula it is considered as a positive test.
• Is 94% sensitive and 100% specific.

Vaccination

• Post-exposure Prophylaxis: If a person bears a tetanus-prone wound such as wounds contaminated with dirt, soil, saliva and feces, punctured wounds, wounds from burns, crushing and frostbite and has incomplete vaccination status should receive antitoxins as well as tetanus toxoid vaccination.
• Tetanus vaccine is routinely given to children as a part of the diphtheria and tetanus toxoids and acellular pertussis dose. 
• This vaccine consists of 5 doses, generally given in the thigh or arm of children when they are aged: 2 months, 4 months, 6 months, 15 to 18 months and 4 to 6 years. 
•  First booster dose is given at age of 11 to 18 years while another booster dose is given every 10 years.
• Individual travelling to tetanus prone areas should consult a doctor about vaccinations.
• A booster dose is recommended at the third trimester of a pregnancy, regardless of the mother’s vaccination schedule.

Treatments

• In treating stiffness and spasms, patients are prescribed following medications:

• Anti-convulsants, such as diazepam, relax muscles by preventing spasms, helps in reduction of anxiety, and work as a sedative.
• Baclofen, a muscle relaxants suppresses nerve signals from the brain to the spinal cord causing less tension in muscle.
• Neuromuscular blocking agents such as pancuronium and vecuronium blocks the signals from nerves to muscle fibers and are used in controlling muscle spasms.
• Antibiotics such as Metronidazole or Penicillin are prescribed.
• Tetanus immune globulin is used to neutralize the toxin.
• Surgery
• If the wound caused by tetanus is huge, they may be removed surgically.
• Nutrition
• Requires a high daily calorie intake due to increased activity of muscle.
• Ventilator
• If vocal cords or respiratory muscles are affected, patients may need support of a ventilator to assist in breathing.
• Vaccination
• It is the main preventive measure.

Prevention and Control

• Clean the wound immediately with soap and water and cover properly with waterproof adhesive dressings until healed.
• Maintain proper hand hygiene before and after touching wounds.
• Wounds should be regularly assessed.
• Protective footwear and gloves should be used while handling rusty and sharp objects.
• If wounds are deep and contaminated, seek medical help.

Conclusion

C. tetani is the most common bacteria found in soil and intestinal tracts of animals which infect people through wounds, burns causing potentially fatal disease known as tetanus. Tetanus is an illness triggered mainly by the production of neurotoxin (tetanospasmin). Early diagnosis and treatment are important, especially in developing countries with limited access to vaccination, highlighting the necessity of routine immunization and addressing challenges in healthcare in low-resource countries. Vaccinations are the main preventive measures which are used in controlling infection by C. tetani.

References

1. BrainKart. (n.d.). Clostridium tetani. BrainKart. https://www.brainkart.com/article/Clostridium-Tetani_41015/
2. Centers for Disease Control and Prevention (CDC). (2024, April 25). Chapter 21: Tetanus. In Epidemiology and Prevention of Vaccine-Preventable Diseases (Pink Book). https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-21-tetanus.html
3. Elsevier. (n.d.). Clostridium tetani. ScienceDirect Topics. https://www.sciencedirect.com/topics/medicine-and-dentistry/clostridium-tetani
4. Swedish University of Agricultural Sciences. (2023, March 8). Clostridium tetani. VetBact. https://www.vetbact.org/?artid=32
5. George, E. K., De Jesus, O., Tobin, E. H., & Vivekanandan, R. (2024, February 26). Tetanus (Clostridium tetani infection). In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482484/
6. European Centre for Disease Prevention and Control. (2025, September 16). Tetanus: Annual epidemiological report for 2023. ECDC. https://www.ecdc.europa.eu/en/publications-data/tetanus-annual-epidemiological-report-2023
7. European Centre for Disease Prevention and Control. (2025, September 16). Tetanus: Annual epidemiological report for 2023. ECDC. https://www.ecdc.europa.eu/en/publications-data/tetanus-annual-epidemiological-report-2023
8. The Open University. (n.d.). Clostridium tetani. OpenLearn Create. https://www.open.edu/openlearncreate/mod/oucontent/view.php?id=86&section=8.5.2
9. Mayo Clinic. (n.d.). Tetanus: Symptoms and causes. Retrieved February 24, 2026, from https://www.mayoclinic.org/diseases-conditions/tetanus/symptoms-causes/syc-20351625
10. Communicable Diseases Agency. (2025, July 15). Tetanus. https://www.cda.gov.sg/professionals/diseases/tetanus/
11. Medical News Today. (2023, June 26). Tetanus: Symptoms, causes, and treatments. https://www.medicalnewstoday.com/articles/163063