Clostridium tetani - MegaMicro

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Clostridium tetani

Micro > Bacteriology > Anaerobic bacteria > Clostridium
a. Structure
i. Gram-positive
ii. Bacillus (rod-shaped); drum-stick appearance
iii. Flagella
iv. Spore-forming
b. Pathobiology:
i. Anaerobic
ii. In vegetative state, it is heat sensitive. However, spores are resistant to heat and some antiseptics, and can last for months-years in soil
iii. Spores can enter host through open wounds, lacerations or burns. The spores germinate and produce toxin. Toxin enters the CNS and blocks inhibition of spinal motor reflexes.
iv. Virulence factors
1. Produces exotoxins: tetanospasmin and tetanolysin
a. Tetanospasmin - primary viruence factor
i. Produced during the stationary phase of growth and released when cell lyses
ii. Binds to motor neurons and is internalized, and transported to the spinal cord
iii. Inactivates proteins that regulate release of glycine and GABA (inhibitory neurotransmitters), leading to unregulated excitatory synaptic activity
b. Tetanolysin
i. toxin of unknown function

c. Epidemiology
i. Spores are commonly found in soil, animal feces, and in human and animal intestinal tracts. Introduced in humans via deep wound trauma (classically a rusty nail)

d. Laboratory diagnosis
i. Stains gram-positive, but can stain gram-negative in older cultures
ii. Organism recovered from wound in only 30% of cases
1. Organism doesn’t survive exposure to air

e. Disease manifestations
i. Diagnosis --> clinical presentation
1. Tetanus causes unopposed muscle contraction and spasm, resulting in spastic paralysis.
ii. Subtypes
1. Generalized tetanus (most common form)
a. Trismus
b. Stiffness of the neck
c. Difficulty swallowing
d. Rigidity of abdominal muscles
e. Drooling, sweating, irritability
f. Back spasms
g. Arrhythmias
h. Fluctuations in blood pressure
2. Localized tetanus
a. Confined to muscles at the site of primary infection
b. Can be cephalic tetanus (involving the face), which carries a poor prognosis
3. Neonatal
a. Infection of umbilical stump
b. generalized
c. Mortality is 90%
iii. Differential diagnosis
1. Strychnine poisoning
a. Primarily used today as a pesticide
b. Symptoms can include muscle spasms, arching of neck and back, rigid arms and legs, jaw tightness, muscle soreness, fever
2. Conditions that may cause trismus
a. Dental infections/abscesses
b. Neoplasms
c. Encephalitis

iv. Therapy
1. Wound care
a. Clean and debride wounds
2. Medications to ease symptoms
a. Antibiotics used to prevent multiplication of C.tetani
i. Penicillin
ii. Metronidazole
b. Drugs used to treat muscle spasm, rigidity and seizures include sedative-hypnotic agents, general anesthetics, centrally acting muscle relaxants and neuromuscular blocking agents
c. Tetanus immune globulin: antitoxin; antibody binds free toxin
3. Supportive therapy
a. Toxin binding is irreversible so recovery depends on formation of new axonal terminals

v. Prevention and control
1. Toxoid Vaccine:
a. Vaccine targets the toxin not the bacteria.
b. Vaccinations (DTaP, Tdap, Td)

Related concepts

Key Words
Tetanus
Spore
Tetanospasmin
Muscle spasm
Spastic paralysis
Trismis
Metronidazole

 
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