Clostridium tetani
Jennifer O'hara
Clostridium tetani is a gram positive sporeforming rod with a clubbed appearance that upon entry to an animal can cause tetanus in the host.  This bacterium is a strict anaerobe that has optimal growth at 37ºC and cannot grow at temperatures 45ºC or above.  Its shape consists of straight rods with terminal spherical spores, without exsporia or appendages.  Most strains of C. tetani are motile with peritrichous flagella, however some are not motile. 

The primary environment in which C. tetani is found is in soil, although it can also sometimes be found in the feces of animals.  The growth factors of all strains of C. tetani include biotin, folic acid, nicotinic acid, pantothenate, pyridoxamine, and uracil.  Some other strains also need adenine, oleic acid, riboflavine, and thiamin to germinate.  C. tetani was found in one-third of the samples of soil examined throughout the world.  However, C. tetani has no invasive ability and can only enter tissue through a puncture or deep wound.  Rusty nails are the most common source of infection, but C. tetani can also infect through burns, ulcers, compound fractures, operative wounds, or drug injections. 

Once in an animal, C. tetani will release two different forms of toxins, a spasmogenic neurotoxin, structurally related to botulinum neurotoxin, and an oxygen-sensitive hemolysin.  The spasmogenic neurotoxin is composed of two disulfide-linked H and L chains.  The L chain blocks the release of the neurotransmitter substance, glycine or gamma animo butyric acid, in the inhibitory nerve system of the spinal cord.  This results in opposing muscles being in a constant state of contraction, rather than the normal movement between contraction and relaxation.  Due to the fact that these spasms can involve the jaws, the disease tetanus has also been referred to as “lockjaw”.  This lockjaw symptom is the first one in humans that contract this disease.

All forms of animals are not equally sensitive to C. tetani.  The most sensitive animals to this anaerobe are humans and horses.  Progressing down the line dogs, cats, and birds are much less sensitive to the toxin produced by C. tetani and would need a much greater amount to be present in them to be fatal.  In addition, the incubation period of tetanus varies from a few days to several weeks, with mortality being higher in those cases with shorter incubation periods. 

If one is diagnosed with tetanus, C. tetani can be recovered from the wounds in unimmunized patients.  However, most patients in the United States undergo immunization with four shots being given during the first two years of birth and then another booster shot being administered every ten years.  Unfortunately, in less developed, third world countries the incidence rate of tetanus is much higher than the United States, especially in neonatal cases where the umbilical cord is cut off with a non-sterile tool.  In fact, over a half million infants died in 1992 internationally from neonatal tetanus.

I chose to do my report on this microbe because I am interested in medicine, especially neurology and because C. tetani releases a neurotoxin, I found it interesting.

Microbial Life 2nd Edition. By Staley, Gunsalus, Lory and Perry

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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