Transcript Clostridia tetani

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Anaerobic Bacteria
Obligate Anaerobes
In the presence of oxygen, anaerobic
bacteria produce toxic products such as
superoxide and hydrogen peroxide, but
they lack superoxide dismutase (SOD),
catalase and peroxidase that detoxify
these products:
SOD:
O2-+2H+  H2O2
Catalase:
H2O2  H2O + O2
Peroxidase: H2O2  H2O /NAD to NADH
No oxidative phosphorylation
Infection caused by anaerobes usually
occurs in the sites with low oxidationreduction potential such as periodontal
pocket, intestinal tract and vagina.
Anaerobes are co-infected with other
facultative anaerobe which use up
oxygen to establish a local anaerobic
environment.
Source of anaerobic infection
Endogenous infection: caused by
anaerobes of normal flora which are nonspore formers.
Exogenous infection: The pathogens are
usually anaerobic spore-formers and come
from the environment (e.g., soil). Clostridia
is the unique genus of anaerobic sporeformers to cause human diseases.
Clostridia
There are at least 118 species, the
clinically important species:
Clostridia tetani
Clostridia perfringens
Clostridia botulinum
Clostridia difficile
Clostridium tetani
spore
vegetative
Gram-positive rods that form terminal
spores
Culture: clustering growth with hemolysis
occurs on blood agar.
Biochemical activity: does not ferment
any carbohydrates.
Resistance: spores but not its
vegetative form can tolerate boiling for
60 min and stay alive for several ten
years in soil.
Clostridia tetani is found in soil. It is
occasionally found in intestinal flora of
humans and animals.
Clostridia tetani is the cause of tetanus
when the spores enter wounds.
Process to cause tetanus
Spore-contaminated soil or other foreign objects
•Narrow deep wounds with limited
blood and oxygen supply
•co-infection
with
facultative
anaerobe can use up the local
oxygen
Spores germinate and then produce tetanus toxins.
The organism still remains in the local wound.
Clostridia tetani produces two exotoxins
called tetanus toxins:
Tetanolysin: its virulent role remains
unknown.
Tetanospasmin: it is a neurotoxin with
strong toxicity and the most important
virulent factor of the bacterium.
Pathogenesis of tetanospasmin
one heavy chain (H chain)
C end：binds to the ganglioside receptors of
inhibitory neurones
N end：helps in entrance to the cells
one light chain (L chain)
It contains a zinc endopeptidase
Blocks the release of inhibitory neuronal mediators
g-GABA (g-氨基丁酸) and glycin (甘氨酸)
Stops inhibitory nerve impulse to skeletal muscles,
resulting in persistent muscle contraction.
Typical symptoms include sardonic smile,
lockjaw, neck rigidity, opisthotonos and
dyspnea
This baby has tetanus. The infection is usually caused by
exposing to Clostridia tetani when cutting umbilical cord.
This the neonatal tetanus patient displays
sardonic smile, lockjaw and dyspnea
The adult tetanus patient shows opisthotonos
Among all animal species, horses and
humans, are most susceptible to
tetanospasmin
If not treated in time, about 20% of the
patients are died of suffocation and
respiratory failure
The wound is treated by debridement
(清创术) to destroy anaerobic
environment.
Although antibiotics (streptomycin and
erythromycin) are used as part of the
treatment, tetanus patients must be
promptly treated with tetanus antitoxin
(TAT) to neutralize free tetanospasmin.
1500 ~ 3000 U for prevention
100.000 ~ 200.000 U for therapy
Tetanus toxoid is a component of DPT
vaccine (diphtheria toxoid, killed whole
cell pertussis, tetanus toxoid).
Clostridia
There are at least 118 species, the
clinically important species:
Clostridia tetani
Clostridia perfringens
Clostridia botulinum
Clostridia difficile
•
Gram-positive rods, have capsule, can form terminal spores
•
Form double hemolysis circles on blood agar plates.
•
The α-hemolysis is caused byα-toxin while the β-hemolysis
byθ-toxin.
Stormy fermentation
Clostridium perfringens shows “stormy
fermentation” in litmus milk. Acid turns
the pH indicator litmus from blue to
pink. The acid and enzymes coagulate
proteins to curd. The gas generated in
the milk breaks the coagulated proteins.
Diseases
Wound contaminated by soil (main
source) and mammalian feces
Gas gangrene refers to serious tissue
swelling due to release of gas
(fermentation product of the bacterium)
and tissue necrosis
The death can occur within 2 days if
untreated. Treatment includes
debridement, antitoxin and antibiotic
therapy.
Diseases
Common diseases:
•Gas gangrene
•Food poisoning
Other diseases:
•Necrotizing Enteritis
•Cellulitis (蜂窝织炎)
•Septicemia
Food poisoning
Marked hypersecretion in jejunum and
ileum with loss of fluids and electrolytes
in diarrhea.
Necrotizing enteritis
an acute necrotizing process in the
jejunum with symptoms of abdominal
pain, bloody diarrhea and peritonitis.
The death rate of this disease is as high
as approximately 50%.
Virulent factors
Clostridium perfringens produces over
10 types of toxins. Some toxins are
hemolytic, proteolytic, saccharolytic
enzymes. Some are lethal and necrotic.
alpha-toxin is the most important, it
lyses erythrocytes, platelets, leukocytes
and endothelial cells.
According to antigenic differences of 4
major toxins, the bacterial strains can
be divided into A~E toxic types.
Type A is clinically the most important.
Type A can also produce enterotoxin to
cause food poisoning.
Morphology
Stormy fermentation
alpha-toxin (lecithinase)
Debridement (Gas gangrene)
A large dose of antibiotics (penicillin)
Antitoxin against alpha-toxin and
hyperbaric oxygenation (高压氧疗法)
No vaccine is available
Clostridia
There are at least 118 species, the
clinically important species:
Clostridia tetani
Clostridia perfringens
Clostridia botulinum
Clostridia difficile
Clostridium botulinum
Clostridium botulinum is a Gram-positive, anaerobic,
spore-forming bacillus.
It produces an enterotoxin (botulinum toxin) that
causes food poisoning (botulism).
According to the antigenicity of botulinum toxin,
The microbe can be divided into A~G types.
Among the 7 types, type A and then type B strains
cause most disease.
The foods that are easily contaminated by the
toxins or spores are sausage and canned foods
abroad, and fermented-bean preparations in China.
In adult, the toxin or spore causes botulism (death
rate 50-70%).
In infant (especially younger than 6 months), the
toxin or spore causes infant botulism (death rate 12%) .
Pathogenesis of botulinum toxin
Botulinum toxin is a nuerotoxin. It binds
to other non-toxic proteins to form a
complex. It is released, when the
bacteria are dead and broken.
When the complex enters intestines,
the alkaline condition makes botulinum
toxin released.
Botulinum toxin binds the cellular
receptor of neuromuscular junction
and then enters the cells to block the
release of acetylcholine (乙酰胆碱).
Acetylcholine is a neurotransmitter,
which mediates nerve impulses.
Therefore, flaccid paralysis occurs.
The typical symptoms are double vision
and squint (eye), dyscatabrosis (throat),
and dyspnea. The patients are usually
died of respiratory failure.
10 ng of Botulinum toxin can kill an
adult.
• Sample collection: foods and patients’
feces.
• Identification of botulinum toxin in the
samples
The patients must be promptly treated with A,
B, E multi-valent antitoxin to neutralize the
free toxins.
Sometimes antibiotic therapy is needed.
Vaccination does not protect hosts from
botulism.
•Non-spore-forming anaerobes are strict anaerobes
and present in large numbers in intestine (95-99% of
the total bacterial mass), mouth and genitourinary
tract as normal flora.
•These anaerobes can be divided into anaerobic Grampositive or negative cocci or rods belonging to 23
genera. 11 genera are associated with human diseases.
Non-Spore-forming Anaerobes
of medical Importance
•Gram-negative rods
Bacteroides, Prevotella, Porphyromonas, Fusobacterium
•Gram-positive rods
Propionibacterium, Actinomyces, Eubacterium, Bifidobacterium
•Gram-positive cocci
Peptostreptococcus, Peptococcus
•Gram-negative cocci
Veillonella
• Most
non-spore-forming
anaerobes
are
opportunistic pathogens, and a few of them show
relatively stronger pathogenicity.
• Co-infection with facultative bacteria.
• Adhesion to host cells by pili.
• Production of various virulent factors such as
enterotoxin, collagenase, hyaluronidas, protease,
hemolysin, DNase.
• Oral, genitourinary, abdominal
infections are most common.
and
perineal
Most infections cause chronic pyogenic
inflammation, local abscess or tissue
necrosis.
The secretion or pus in foci are usually
colored (black, brown, bloody, pink),
putrid and gas-producing.
• Direct microscopy examination: to observe the
bacteria in the smear of secretion.
• Typical bacteriological examination: to isolate and
identify the anaerobes from samples. In smear of
secretion, bacteria can be seen, whereas the
results of common cultivations are negative.
1. Aminoglycoside antibiotics (e.g., streptomicin)
and some β-lactam antibiotics are ineffective.
2. Antibiotics such as nitrominazole (metronidazole)
are used for treatment.
2. No vaccines are available.